Ecological Applications, Volume 24, Issue 5, Page 1144-1154, July 2014.
Climate change vulnerability assessments for species of conservation concern often use species distribution and ecological niche modeling to project changes in habitat. One of many assumptions of these approaches is that food web dependencies are consistent in time and environmental space. Species at higher trophic levels that rely on the availability of species at lower trophic levels as food may be sensitive to extinction cascades initiated by changes in the habitat of key food resources. Here we assess climate change vulnerability for Ursus arctos (grizzly bears) in the southern Canadian Rocky Mountains using projected changes to 17 of the most commonly consumed plant food items. We used presence–absence information from 7088 field plots to estimate ecological niches and to project changes in future distributions of each species. Model projections indicated idiosyncratic responses among food items. Many food items persisted or even increased, although several species were found to be vulnerable based on declines or geographic shifts in suitable habitat. These included Hedysarum alpinum (alpine sweet vetch), a critical spring and autumn root-digging resource when little else is available. Potential habitat loss was also identified for three fruiting species of lower importance to bears: Empetrum nigrum (crowberry), Vaccinium scoparium (grouseberry), and Fragaria virginiana (strawberry). A general trend towards uphill migration of bear foods may result in higher vulnerability to bear populations at low elevations, which are also those that are most likely to have human–bear conflict problems. Regardless, a wide diet breadth of grizzly bears, as well as wide environmental niches of most food items, make climate change a much lower threat to grizzly bears than other bear species such as polar bears and panda bears. We cannot exclude, however, future alterations in human behavior and land use resulting from climate change that may reduce survival rates.
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27 Dec 09:09
Idiosyncratic responses of grizzly bear habitat to climate change based on projected food resource changes
by onlinepublishing@allenpress.com (David R. Roberts et al)
27 Dec 09:09
Planning Across Freshwater and Terrestrial Realms: Cobenefits and Tradeoffs Between Conservation Actions
by Vanessa M. Adams, Jorge G. Álvarez-Romero, Josie Carwardine, Lorenzo Cattarino, Virgilio Hermoso, Mark J. Kennard, Simon Linke, Robert L. Pressey, Natalie Stoeckl
Abstract
Conservation planning has historically been restricted to planning within single realms (i.e., marine, terrestrial, or freshwater). Recently progress has been made in approaches for cross-realm planning which may enhance the ability to effectively manage processes that sustain biodiversity and ecosystem functions (e.g., connectivity) and thus minimize threats more efficiently. Current advances, however, have not optimally accounted for the fact that individual conservation management actions often have impacts across realms. We advance the existing cross-realm planning literature by presenting a conceptual framework for considering both co-benefits and tradeoffs between multiple realms (specifically freshwater and terrestrial). This conceptual framework is founded on a review of 1) the shared threats and management actions across realms and 2) existing literature on cross-realm planning to highlight recent research achievements and gaps. We identify current challenges and opportunities associated with the application of our framework and consider the more general prospects for cross-realm planning.
27 Dec 09:08
PERMANOVA, ANOSIM, and the Mantel test in the face of heterogeneous dispersions: What null hypothesis are you testing?
by onlinepublishing@allenpress.com (Marti J. Anderson et al)
Ecological Monographs, Volume 83, Issue 4, Page 557-574, November 2013.
ANOSIM, PERMANOVA, and the Mantel test are all resemblance-based permutation methods widely used in ecology. Here, we report the results of the first simulation study, to our knowledge, specifically designed to examine the effects of heterogeneity of multivariate dispersions on the rejection rates of these tests and on a classical MANOVA test (Pillai's trace). Increasing differences in dispersion among groups were simulated under scenarios of changing sample sizes, correlation structures, error distributions, numbers of variables, and numbers of groups for balanced and unbalanced one-way designs. The power of these tests to detect environmental impacts or natural large-scale biogeographic gradients was also compared empirically under simulations based on parameters derived from real ecological data sets. Overall, ANOSIM and the Mantel test were very sensitive to heterogeneity in dispersions, with ANOSIM generally being more sensitive than the Mantel test. In contrast, PERMANOVA and Pillai's trace were largely unaffected by heterogeneity for balanced designs. PERMANOVA was also unaffected by differences in correlation structure, unlike Pillai's trace. For unbalanced designs, however, all of the tests were (1) too liberal when the smaller group had greater dispersion and (2) overly conservative when the larger group had greater dispersion, especially ANOSIM and the Mantel test. For simulations based on real ecological data sets, PERMANOVA was generally, but not always, more powerful than the others to detect changes in community structure, and the Mantel test was usually more powerful than ANOSIM. Both the error distributions and the resemblance measure affected results concerning power. Differences in the underlying construction of these test statistics result in important differences in the nature of the null hypothesis they are testing, their sensitivity to heterogeneity, and their power to detect important changes in ecological communities. For balanced designs, PERMANOVA and PERMDISP can be used to rigorously identify location vs. dispersion effects, respectively, in the space of the chosen resemblance measure. ANOSIM and the Mantel test can be used as more “omnibus” tests, being sensitive to differences in location, dispersion or correlation structure among groups. Unfortunately, none of the tests (PERMANOVA, Mantel, or ANOSIM) behaved reliably for unbalanced designs in the face of heterogeneity.
ANOSIM, PERMANOVA, and the Mantel test are all resemblance-based permutation methods widely used in ecology. Here, we report the results of the first simulation study, to our knowledge, specifically designed to examine the effects of heterogeneity of multivariate dispersions on the rejection rates of these tests and on a classical MANOVA test (Pillai's trace). Increasing differences in dispersion among groups were simulated under scenarios of changing sample sizes, correlation structures, error distributions, numbers of variables, and numbers of groups for balanced and unbalanced one-way designs. The power of these tests to detect environmental impacts or natural large-scale biogeographic gradients was also compared empirically under simulations based on parameters derived from real ecological data sets. Overall, ANOSIM and the Mantel test were very sensitive to heterogeneity in dispersions, with ANOSIM generally being more sensitive than the Mantel test. In contrast, PERMANOVA and Pillai's trace were largely unaffected by heterogeneity for balanced designs. PERMANOVA was also unaffected by differences in correlation structure, unlike Pillai's trace. For unbalanced designs, however, all of the tests were (1) too liberal when the smaller group had greater dispersion and (2) overly conservative when the larger group had greater dispersion, especially ANOSIM and the Mantel test. For simulations based on real ecological data sets, PERMANOVA was generally, but not always, more powerful than the others to detect changes in community structure, and the Mantel test was usually more powerful than ANOSIM. Both the error distributions and the resemblance measure affected results concerning power. Differences in the underlying construction of these test statistics result in important differences in the nature of the null hypothesis they are testing, their sensitivity to heterogeneity, and their power to detect important changes in ecological communities. For balanced designs, PERMANOVA and PERMDISP can be used to rigorously identify location vs. dispersion effects, respectively, in the space of the chosen resemblance measure. ANOSIM and the Mantel test can be used as more “omnibus” tests, being sensitive to differences in location, dispersion or correlation structure among groups. Unfortunately, none of the tests (PERMANOVA, Mantel, or ANOSIM) behaved reliably for unbalanced designs in the face of heterogeneity.
27 Dec 09:08
Under niche construction: an operational bridge between ecology, evolution, and ecosystem science
by onlinepublishing@allenpress.com (Blake Matthews et al)
Ecological Monographs, Volume 84, Issue 2, Page 245-263, May 2014.
All living organisms modify their biotic and abiotic environment. Niche construction theory posits that organism-mediated modifications to the environment can change selection pressures and influence the evolutionary trajectories of natural populations. While there is broad support for this proposition in general, there is considerable uncertainty about how niche construction is related to other similar concepts in ecology and evolution. Comparative studies dealing with certain aspects of niche construction are increasingly common, but there is a troubling lack of experimental tests of the core concepts of niche construction theory. Here, we propose an operational framework to evaluate comparative and experimental evidence of the evolutionary consequences of niche construction, and suggest how such research can improve our understanding of ecological and evolutionary dynamics in ecosystems. We advocate for a shift toward explicit experimental tests of how organism-mediated environmental change can influence the selection pressures underlying evolutionary responses, as well as targeted field-based comparative research to identify the mode of evolution by niche construction and assess its importance in natural populations.
All living organisms modify their biotic and abiotic environment. Niche construction theory posits that organism-mediated modifications to the environment can change selection pressures and influence the evolutionary trajectories of natural populations. While there is broad support for this proposition in general, there is considerable uncertainty about how niche construction is related to other similar concepts in ecology and evolution. Comparative studies dealing with certain aspects of niche construction are increasingly common, but there is a troubling lack of experimental tests of the core concepts of niche construction theory. Here, we propose an operational framework to evaluate comparative and experimental evidence of the evolutionary consequences of niche construction, and suggest how such research can improve our understanding of ecological and evolutionary dynamics in ecosystems. We advocate for a shift toward explicit experimental tests of how organism-mediated environmental change can influence the selection pressures underlying evolutionary responses, as well as targeted field-based comparative research to identify the mode of evolution by niche construction and assess its importance in natural populations.
27 Dec 09:07
Historical range of fire frequency is not the Achilles' heel of the Corsican black pine ecosystem
by Bérangère Leys, Walter Finsinger, Christopher Carcaillet
Summary
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This study investigated the fire-vegetation relationship by reconstructing the long-term fire and vegetation dynamics around a small lake in the Mediterranean montane belt on Corsica Island. The vegetation is characterised by forests dominated by Pinus nigra ssp. laricio, an endemic subspecies that is currently threatened. Populations of this taxon are geographically restricted, and their ranges are decreasing, possibly because of disturbance, that is, fire and logging.
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Here, we examine the role of fire in vegetation dynamics and its effect on diversity since the lateglacial at a montane site using sedimentary plant macrofossils and charcoal to reconstruct local vegetation and fire frequency, respectively.
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Macrofossils of P. laricio provide evidence for its growth around the Lac de Creno since 13 200 cal. years bp, which is consistent with its natural origin in Corsica. The onset of the Holocene (~11 700 cal. years bp) was marked by a rapid shift in the treeline, the establishment of P. laricio-dominated woodlands with low species turnover, and a long-term increase in taxa richness as a result of successive expansions of broadleaved deciduous trees. In spite of fire-return intervals (FRIs) fluctuating between 30 and 490 years during the Holocene, P. laricio-dominated woodlands persisted for several millennia, and fires likely played an ecological role in the functioning of these woodlands. The 12 000 year record of mean FRI (80 years between fires; i.e. frequency of 12.5 fires 1000 year−1) can be used to define a baseline for the management and conservation of P. laricio montane forests. Our findings demonstrate that P. laricio has a long history, a natural origin in Corsica, and that Corsican pine forests have survived to a wide range of burning conditions over the last 13 200 years.
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Synthesis: We present multimillennial fire and vegetation histories of a Mediterranean montane site. Pinus nigra ssp. laricio has been present near the study site since approximately 13 200 cal. years bp, demonstrating that this pine was present on the island prior to the arrival of pre-historic humans. The long-term records also show that P. laricio woodlands were mixed with deciduous broadleaf trees (Betula sp. and Fagus sylvatica), and other needleleaf trees (Abies alba), at least, and were not influenced by changes in fire frequency. We conclude that (i) fire is a natural component of the ecosystem and (ii) fires likely played an important ecological role in the functioning of the Corsican black pine woodland ecosystem.
Corsican black pine and fires were present since 13 200 cal. years bp at least on the island prior to the arrival of prehistoric humans. The long-term records also show that P. laricio woodlands were mixed with deciduous broadleaf trees, and other needleleaf trees, and were not influenced by changes in fire frequency. We conclude that (i) fire is a natural component of the ecosystem and that (ii) fires likely played an important ecological role in the functioning of the Corsican black pine woodland ecosystem.
27 Dec 09:07
Determining habitat suitability for bumblebees in a mountain system: a baseline approach for testing the impact of climate change on the occurrence and abundance of species
by José M. Herrera, Emilie F. Ploquin, Javier Rodríguez-Pérez, José R. Obeso
Abstract
Aim
Our aim was to determine the role of environmental variables in explaining occurrence and abundance patterns of bumblebee (Bombus) species in a mountain region. We also used a historical dataset to compare historical and recent habitat suitability predictions for forecasting variations in species' responses to regional climate warming.
Location
The Cantabrian Range (Iberian Peninsula, south-western Europe).
Methods
During 2007–09 we sampled bumblebees in 37 localities and developed generalized linear models (GLMs) to predict species' occurrence and abundance in relation to environmental variables. We extracted independent variables at different spatial scales for each locality, based on topoclimatic (slope, temperature and rainfall patterns) and land-cover (habitat configuration and composition) variables. We also used historical (1988–89) bumblebee data (23 localities) to both calibrate recent distribution models and determine the current environmental factors underlying the realized response of individual species to regional climate warming (0.8 °C) over two decades.
Results
Occurrence and abundance patterns of species were best predicted by models combining topoclimatic and land-cover variables. Our findings revealed three groups of species, distinguished on the basis of the realized response of individual species to regional climate warming: one comprising six species with climate-based tracking behaviour, a second with three species tracking suitable landscape composition and configuration regardless of climatic conditions, and a third comprising one species showing no apparent tracking behaviour.
Main conclusions
Topoclimate and land cover determined the occurrence and abundance patterns of bumblebee species in mountainous landscapes, even at fine spatial extents. Both environmental variables, however, differentially influenced bumblebees, thereby providing relevant clues for determining the current environmental factors underlying species' distributions and their susceptibility to changing environmental conditions. Our findings therefore suggest that determining habitat suitability can be used as a baseline approach for understanding species-specific responses to climate warming and for developing vulnerability assessments for conservation-focused management planning.
27 Dec 09:06
Predicting local and non-local effects of resources on animal space use using a mechanistic step selection model
by Jonathan R. Potts, Guillaume Bastille-Rousseau, Dennis L. Murray, James A. Schaefer, Mark A. Lewis
Summary
- Predicting space use patterns of animals from their interactions with the environment is fundamental for understanding the effect of habitat changes on ecosystem functioning. Recent attempts to address this problem have sought to unify resource selection analysis, where animal space use is derived from available habitat quality, and mechanistic movement models, where detailed movement processes of an animal are used to predict its emergent utilization distribution. Such models bias the animal's movement towards patches that are easily available and resource-rich, and the result is a predicted probability density at a given position being a function of the habitat quality at that position. However, in reality, the probability that an animal will use a patch of the terrain tends to be a function of the resource quality in both that patch and the surrounding habitat.
- We propose a mechanistic model where this non-local effect of resources naturally emerges from the local movement processes, by taking into account the relative utility of both the habitat where the animal currently resides and that of where it is moving. We give statistical techniques to parametrize the model from location data and demonstrate application of these techniques to GPS location data of caribou (Rangifer tarandus) in Newfoundland.
- Steady-state animal probability distributions arising from the model have complex patterns that cannot be expressed simply as a function of the local quality of the habitat. In particular, large areas of good habitat are used more intensively than smaller patches of equal quality habitat, whereas isolated patches are used less frequently. Both of these are real aspects of animal space use missing from previous mechanistic resource selection models.
- Whilst we focus on habitats in this study, our modelling framework can be readily used with any environmental covariates and therefore represents a unification of mechanistic modelling and step selection approaches to understanding animal space use.
27 Dec 09:06
Ecological production functions for biological control services in agricultural landscapes
by Mattias Jonsson, Riccardo Bommarco, Barbara Ekbom, Henrik G. Smith, Jan Bengtsson, Berta Caballero-Lopez, Camilla Winqvist, Ola Olsson
Summary
- Research relating to ecosystem services has increased, partly because of drastic declines in biodiversity in agricultural landscapes. However, the mechanistic linkages between land use, biodiversity and service provision are poorly understood and synthesized. This is particularly true for many ecosystem services provided by mobile organisms such as natural enemies to crop pests. These species are not only influenced by local land use but also by landscape composition at larger spatial scales.
- We present a conceptual ecological production function framework for predicting land-use impact on biological control of pests by natural enemies. We develop a novel, mechanistic landscape model for biological control of cereal aphids, explicitly accounting for the influence of landscape composition on natural enemies varying in mobility, feeding rates and other life history traits. Finally, we use the model to map biological control services across cereal fields in a Swedish agricultural region with varying landscape complexity.
- The model predicted that biological control would reduce crop damage by 45–70% and that the biological control effect would be higher in complex landscapes. In a validation with independent data, the model performed well and predicted a significant proportion of biological control variation in cereal fields. However, much variability remains to be explained, and we propose that the model could be improved by refining the mechanistic understanding of predator dynamics and accounting for variation in aphid colonization.
- We encourage scientists working with biological control to adopt the conceptual framework presented here and to develop production functions for other crop-pest systems. If this kind of ecological production function is combined with production functions for other services, the joint model will be a powerful tool for managing ecosystem services and planning for sustainable agriculture at the landscape scale.
27 Dec 09:05
A fire driven shift from forest to non-forest: evidence for alternative stable states?
by onlinepublishing@allenpress.com (Michael-Shawn Fletcher et al)
Ecology, Volume 0, Issue 0, Ahead of Print.
We test the validity of applying the alternative stable state paradigm to account for the landscape-scale forest/non-forest mosaic that prevails in temperate Tasmania, Australia. This test is based on fine scale pollen, spore and charcoal analyses of sediments located within a small patch of non-forest vegetation surrounded by temperate forest. Following nearly 500 years of forest dominance at the site, a catastrophic fire drove an irreversible shift from a forested Cyperaceae-Sphagnum wetland to a non-forested Restionaceae wetland at ca.7000 cal yr BP. Persistence of the non-forest/Restionaceae vegetation state over 7000 years despite long fire-free intervals implies that fire was not essential for the maintenance of the non-forest state. We propose that reduced interception and transpiration of the non-forest state resulted in local waterlogging, presenting an eco-hydrological barrier to forest reestablishment over the succeeding 7000 years. We further contend that the rhizotamous nature of the non-forest species presented a reinforcing eco-physical barrier to forest development. Our results satisfy a number of criteria for consideration as an example of a switch between alternative stable states, including different origin and maintenance pathways, and provide insights into the role of threshold dynamics and hysteresis in forest/non-forest transitions.
We test the validity of applying the alternative stable state paradigm to account for the landscape-scale forest/non-forest mosaic that prevails in temperate Tasmania, Australia. This test is based on fine scale pollen, spore and charcoal analyses of sediments located within a small patch of non-forest vegetation surrounded by temperate forest. Following nearly 500 years of forest dominance at the site, a catastrophic fire drove an irreversible shift from a forested Cyperaceae-Sphagnum wetland to a non-forested Restionaceae wetland at ca.7000 cal yr BP. Persistence of the non-forest/Restionaceae vegetation state over 7000 years despite long fire-free intervals implies that fire was not essential for the maintenance of the non-forest state. We propose that reduced interception and transpiration of the non-forest state resulted in local waterlogging, presenting an eco-hydrological barrier to forest reestablishment over the succeeding 7000 years. We further contend that the rhizotamous nature of the non-forest species presented a reinforcing eco-physical barrier to forest development. Our results satisfy a number of criteria for consideration as an example of a switch between alternative stable states, including different origin and maintenance pathways, and provide insights into the role of threshold dynamics and hysteresis in forest/non-forest transitions.
27 Dec 09:04
Biotic mechanisms of community stability shift along a precipitation gradient
by onlinepublishing@allenpress.com (Lauren Margaret Hallett et al)
Ecology, Volume 95, Issue 6, Page 1693-1700, June 2014.
Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.
Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.
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27 Dec 09:04
Incorporating model complexity and spatial sampling bias into ecological niche models of climate change risks faced by 90 California vertebrate species of concern
by Dan L. Warren, Amber N. Wright, Stephanie N. Seifert, H. Bradley Shaffer
Abstract
Aim
Ecological niche models are increasingly being used to aid in predicting the effects of future climate change on species distributions. Complex models that show high predictive performance on current distribution data may do a poor job of predicting new data due to overfitting. In addition, model performance is often evaluated using techniques that are sensitive to spatial sampling bias. Here, we explore the effects of model complexity and spatial sampling bias on niche models for 90 vertebrate taxa of conservation concern.
Location
California, USA.
Methods
We used Akaike information criterion (AICc) to select variables and tune Maxent's built-in regularization parameter (β) to constrain model complexity. In addition, we incorporated several estimates of spatial sampling bias based on interpolations of target group data. Ensemble forecasts were developed for future conditions from two emission scenarios and three climate change models for the year 2050.
Results
Reducing the number of predictors and tuning β resulted in a reduction in the number of parameters in models built with sample sizes greater than approximately 10 occurrence points. Reducing the number of predictors had a substantially higher impact on the relative prioritization of different grid cells than did increasing regularization. There was little difference in prioritization of habitat when comparing models built using different spatial sampling bias estimates. Over half of the taxa were predicted to experience >80% reductions in environmental suitability in currently occupied cells, and this pattern was consistent across taxonomic groups.
Main Conclusions
Our results demonstrate that reducing the number of correlated predictor variables tends to decrease the breadth of models, while tuning regularization using AICc tends to increase it. These two strategies may provide a reasonable bracketing strategy for assessing climate change impacts.
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27 Dec 09:03
The richness–heterogeneity relationship differs between heterogeneity measures within and among habitats
by Avi Bar-Massada, Eric M. Wood
The positive monotonic relationship between habitat heterogeneity and species richness is a cornerstone of ecology. Recently, it was suggested that this relationship should be unimodal rather than monotonic due to a tradeoff between environmental heterogeneity and population sizes, which increases local species extinctions at high heterogeneity levels. Here, we studied the richness–heterogeneity relationship for an avian community using two different environmental variables, foliage-height diversity and cover type diversity. We analyzed the richness–heterogeneity within different habitat types (grasslands, savannas, or woodlands) and at the landscape scale. We found strong evidence that both positive and unimodal relationships exist at the landscape scale. Within habitats we found positive relationships between richness and heterogeneity in grasslands and woodlands, and unimodal relationships in savannas. We suggest that the length of the environmental heterogeneity gradient (which is affected by both spatial scale and the environmental variable being analyzed) affects the type of the richness–heterogeneity relationship. We conclude that the type of the relationship between species richness and environmental heterogeneity is non-ubiquitous, and varies both within and among habitats and environmental variables.
27 Dec 09:03
Why are there so many species in the tropics?
by James H. Brown
Abstract
Known for centuries, the geographical pattern of increasing biodiversity from the poles to the equator is one of the most pervasive features of life on Earth. A longstanding goal of biogeographers has been to understand the primary factors that generate and maintain high diversity in the tropics. Many ‘historical’ and ‘ecological’ hypotheses have been proposed and debated, but there is still little consensus. Recent discussions have centred around two main phenomena: phylogenetic niche conservatism and ecological productivity. These two factors play important roles, but accumulating theoretical and empirical studies suggest that the single most important factor is kinetics: the temperature dependence of ecological and evolutionary rates. The relatively high temperatures in the tropics generate and maintain high diversity because ‘the Red Queen runs faster when she is hot’.
27 Dec 09:03
Long-term changes in liana abundance and forest dynamics in undisturbed Amazonian forests
by onlinepublishing@allenpress.com (William F. Laurance et al)
Ecology, Volume 95, Issue 6, Page 1604-1611, June 2014.
Lianas (climbing woody vines) are important structural parasites of tropical trees and may be increasing in abundance in response to global-change drivers. We assessed long-term (∼14-year) changes in liana abundance and forest dynamics within 36 1-ha permanent plots spanning ∼600 km2 of undisturbed rainforest in central Amazonia. Within each plot, we counted each liana stem (≥2 cm diameter) and measured its diameter at 1.3 m height, and then used these data to estimate liana aboveground biomass. An initial liana survey was completed in 1997–1999 and then repeated in 2012, using identical methods. Liana abundance in the plots increased by an average of 1.00% ± 0.88% per year, leading to a highly significant (t = 6.58, df = 35, P
Lianas (climbing woody vines) are important structural parasites of tropical trees and may be increasing in abundance in response to global-change drivers. We assessed long-term (∼14-year) changes in liana abundance and forest dynamics within 36 1-ha permanent plots spanning ∼600 km2 of undisturbed rainforest in central Amazonia. Within each plot, we counted each liana stem (≥2 cm diameter) and measured its diameter at 1.3 m height, and then used these data to estimate liana aboveground biomass. An initial liana survey was completed in 1997–1999 and then repeated in 2012, using identical methods. Liana abundance in the plots increased by an average of 1.00% ± 0.88% per year, leading to a highly significant (t = 6.58, df = 35, P
27 Dec 09:02
Food predictability determines space use of endangered vultures: implications for management of supplementary feeding
by onlinepublishing@allenpress.com (Pascual López-López et al)
Ecological Applications, Volume 24, Issue 5, Page 938-949, July 2014.
Understanding space use of free-living endangered animals is key to informing management decisions for conservation planning. Like most scavengers, vultures have evolved under a context of unpredictability of food resources (i.e., exploiting scattered carcasses that are intermittently available). However, the role of predictable sources of food in shaping spatial ecology of vultures has seldom been studied in detail. Here, we quantify the home range of the Egyptian Vulture (Neophron percnopterus), a long-lived raptor that has experienced severe population decline throughout its range and is qualified as endangered worldwide. To this end, six adults were tracked by satellite telemetry in Spain during the breeding season, from 2007 to 2012, recording 10 360 GPS locations. Using Resource Utilization Functions, we assessed the topology of the Utilization Distribution, a three-dimensional measure that shows the probability of finding an animal within the home range. Our results showed how food availability, and principally, how food predictability, determines ranging behavior of this species. Egyptian Vultures showed consistent site fidelity across years, measured as the two- and three-dimensional overlap in their home ranges. Space use varied considerably within the home range and remarkably, places located far from nesting sites were used more frequently than some areas located closer. Therefore, traditional conservation measures based on establishing restrictive rules within a fixed radius around nesting sites could be biologically meaningless if other areas within the home range are not protected too. Finally, our results emphasize the importance of anthropogenic predictable sources of food (mainly vulture restaurants) in shaping the space use of scavengers, which is in agreement with recent findings. Hence, measures aimed at ensuring food availability are essential to preserve this endangered vulture, especially in the present context of limiting carrion dumping in the field due to sanitary regulations according to European legislation.
Understanding space use of free-living endangered animals is key to informing management decisions for conservation planning. Like most scavengers, vultures have evolved under a context of unpredictability of food resources (i.e., exploiting scattered carcasses that are intermittently available). However, the role of predictable sources of food in shaping spatial ecology of vultures has seldom been studied in detail. Here, we quantify the home range of the Egyptian Vulture (Neophron percnopterus), a long-lived raptor that has experienced severe population decline throughout its range and is qualified as endangered worldwide. To this end, six adults were tracked by satellite telemetry in Spain during the breeding season, from 2007 to 2012, recording 10 360 GPS locations. Using Resource Utilization Functions, we assessed the topology of the Utilization Distribution, a three-dimensional measure that shows the probability of finding an animal within the home range. Our results showed how food availability, and principally, how food predictability, determines ranging behavior of this species. Egyptian Vultures showed consistent site fidelity across years, measured as the two- and three-dimensional overlap in their home ranges. Space use varied considerably within the home range and remarkably, places located far from nesting sites were used more frequently than some areas located closer. Therefore, traditional conservation measures based on establishing restrictive rules within a fixed radius around nesting sites could be biologically meaningless if other areas within the home range are not protected too. Finally, our results emphasize the importance of anthropogenic predictable sources of food (mainly vulture restaurants) in shaping the space use of scavengers, which is in agreement with recent findings. Hence, measures aimed at ensuring food availability are essential to preserve this endangered vulture, especially in the present context of limiting carrion dumping in the field due to sanitary regulations according to European legislation.
27 Dec 09:02
Contrasting effects of mass-flowering crops on bee pollination of hedge plants at different spatial and temporal scales
by onlinepublishing@allenpress.com (Anikó Kovács-Hostyánszki et al)
Ecological Applications, Volume 23, Issue 8, Page 1938-1946, December 2013.
Landscape-wide mass-flowering of oilseed rape (canola Brassica napus) can considerably affect wild bee communities and pollination success of wild plants. We aimed to assess the impact of oilseed rape on the pollination of wild plants and bee abundance during and after oilseed-rape bloom, including effects on crop–noncrop spillover at landscape and adjacent-field scales. We focused on two shrub species (hawthorn Crataegus spp., dog rose Rosa canina) and adjacent herb flowering in forest edges, connected hedges, and isolated hedges in Lower Saxony, Germany. We selected 35 landscape circles of 1 km radius, differing in the amount of oilseed rape; 18 were adjacent to oilseed rape and 17 to cereal fields, and we quantified bee density via pan traps at all sites. Adjacent oilseed rape positively affected fruit mass and seed number per fruit of simultaneously flowering hawthorn (no effect on dog rose, which flowers after the oilseed rape bloom). At the landscape scale, oilseed rape had a negative effect on bumble bee density in the hedges during flowering due to dilution of pollinators per unit area and the consequently intensified competition between oilseed rape and wild shrubs, but a positive effect after flowering when bees moved to the hedges, which still provided resources. In contrast, positive landscape-scale effects of oilseed rape were found throughout the season in forest edges, suggesting that edges support nesting activity and enhanced food resources. Our results show that oilseed rape effects on bee abundances and pollination success in seminatural habitats depend on the spatial and temporal scale considered and on the habitat type, the wild plant species, and the time of crop flowering. These scale-dependent positive and negative effects should be considered in evaluations of landscape-scale configuration and composition of crops. Food resources provided by mass-flowering crops should be most beneficial for landscape-wide enhancement of wild bee populations if seminatural habitats are available, providing (1) nesting resources and (2) continuous flowering resources during the season.
Landscape-wide mass-flowering of oilseed rape (canola Brassica napus) can considerably affect wild bee communities and pollination success of wild plants. We aimed to assess the impact of oilseed rape on the pollination of wild plants and bee abundance during and after oilseed-rape bloom, including effects on crop–noncrop spillover at landscape and adjacent-field scales. We focused on two shrub species (hawthorn Crataegus spp., dog rose Rosa canina) and adjacent herb flowering in forest edges, connected hedges, and isolated hedges in Lower Saxony, Germany. We selected 35 landscape circles of 1 km radius, differing in the amount of oilseed rape; 18 were adjacent to oilseed rape and 17 to cereal fields, and we quantified bee density via pan traps at all sites. Adjacent oilseed rape positively affected fruit mass and seed number per fruit of simultaneously flowering hawthorn (no effect on dog rose, which flowers after the oilseed rape bloom). At the landscape scale, oilseed rape had a negative effect on bumble bee density in the hedges during flowering due to dilution of pollinators per unit area and the consequently intensified competition between oilseed rape and wild shrubs, but a positive effect after flowering when bees moved to the hedges, which still provided resources. In contrast, positive landscape-scale effects of oilseed rape were found throughout the season in forest edges, suggesting that edges support nesting activity and enhanced food resources. Our results show that oilseed rape effects on bee abundances and pollination success in seminatural habitats depend on the spatial and temporal scale considered and on the habitat type, the wild plant species, and the time of crop flowering. These scale-dependent positive and negative effects should be considered in evaluations of landscape-scale configuration and composition of crops. Food resources provided by mass-flowering crops should be most beneficial for landscape-wide enhancement of wild bee populations if seminatural habitats are available, providing (1) nesting resources and (2) continuous flowering resources during the season.
27 Dec 09:02
Major declines of woody plant species ranges under climate change in Yunnan, China
by Ming-Gang Zhang, Zhe-Kun Zhou, Wen-Yun Chen, Charles H. Cannon, Niels Raes, J. W. Ferry Slik
Abstract
Aim
A wide range of forests distributed across steep environmental gradients are found in Yunnan, southwest China. Climate change could profoundly change these forests by affecting species ranges. We produce predictions about species suitable habitat shifts and use these to (1) evaluate species range size change, loss and turn-over under no- and full-dispersal and nine climate change scenarios and (2) identify environmental variables responsible for current species richness and future local species losses.
Location
Yunnan Province, Southwest China.
Methods
Using MaxEnt, we modelled current distributions of 2319 woody plant species, corrected for collecting bias and found that 1996 had significant spatial association with environmental factors. Using three General Circulation Models (GCMs: CGCM, CSIRO and HADCM3) for the years 2070–2099 (2080s), based on three emission scenarios for each GCM (A1b, A2a and B2a), we predicted the future geographic position of suitable habitat for each species.
Results
Although most species were predicted to persist within Yunnan, with a maximum extinction rate of c. 6% under the most extreme climate change scenario, up to 1400 species (of the 1996 tested) are expected to lose more than 30% of their current range under the most extreme climate change scenario. Assuming no- or unlimited dispersal minimally affected these outcomes. Species losses were associated with increasing temperature variability and declining precipitation during the dry season.
Main conclusions
To conserve Yunnan's woody flora, management efforts should focus on providing elevational migration routes at local scales, with priority for those areas located within previously identified conservation hotspots. As almost all species show range contractions, storage of genetic diversity in seed banks and botanical gardens would be sensible. A change in Yunnan's conservation policy will be needed to counter the predicted negative impacts of climate change on its flora.
27 Dec 09:01
Commentary on Ditch, Stitch and Pitch: the niche is here to stay
by Jorge Soberón
Abstract
A recent set of discussion papers in the Journal of Biogeography by McInerny and Etienne (henceforth M&E) questions the value of niche concepts in relation to a diverse group of practices collectively labelled species distribution modelling (SDM), and specifically the usefulness of the idea of a fundamental niche. In this Correspondence, I argue that certain types of SDM may indeed dispense with niche concepts, but that such is not the case for an important class of SDM-based activities, including transferring predictions in space and time. Using a single term (SDM) to denote diverse objectives and practices does not help to clarify issues; I discuss this point. I also review several criticisms raised by M&E about the use of the concept of fundamental niche in the context of modelling species' distributions and their environments.
27 Dec 09:01
Pollination and Land Degradation: Top Priorities for New Intergovernmental Body
First Work Plan and Budget for The Intergovernmental Platform for Biodiversity and Ecosystem Services (IPBES) Approved
23 Dec 17:30
A horizon scan of global conservation issues for 2014
William J. Sutherland, Rosalind Aveling, Thomas M. Brooks, Mick Clout, Lynn V. Dicks, Liz Fellman, Erica Fleishman, David W. Gibbons, Brandon Keim, Fiona Lickorish, Kathryn A. Monk, Diana Mortimer, Lloyd S. Peck, Jules Pretty, Johan Rockström, Jon Paul Rodríguez, Rebecca K. Smith, Mark D. Spalding, Femke H. Tonneijck, Andrew R. Watkinson.
• This is the fifth in our annual series of horizon scans published in TREE.
• We identify 15 issues that we considered insufficiently known by the conservatio....
• We identify 15 issues that we considered insufficiently known by the conservatio....
23 Dec 17:29
Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties
by Geraldine Nogaro, Alan D. Steinman
Invasive species may impact biotic community structure, ecosystem processes, and associated goods and services. Their impact may be especially strong when they also serve as ecosystem engineers (i.e. organisms affecting the physical habitat and resources for other species). Dreissenid mussels fill both these roles, having invaded the Laurentian Great Lakes in the late 1980s, and also serve as ecosystem engineers by altering nutrient fluxes and influencing the microbial food web through direct nutrient release and excretion of feces and pseudo-feces at the water–sediment interface. We conducted laboratory experiments to investigate how the different functional traits of invasive quagga mussels (filtering activity and direct nutrient release) and native chironomid larvae (tube building and bioirrigation) interact with lake sediment of differing organic matter content to influence biogeochemical fluxes and water quality. Our results showed that sediment reworking and ventilation activities by chironomid larvae increased oxygen penetration in the sediment, affecting primarily pore water chemistry, whereas invasive mussels enhanced nutrient releases in the surface water. However, sediment organic matter modulated the effects of ecosystem engineers on system-level processes; chironomids had a greater influence on sediment reworking and microbial-mediated processes in organic-rich sediments, whereas quagga mussels enhanced nutrient concentrations in the overlying water of organic-poor sediments. These results have management implications, as the effects of invasive mussels on the biogeochemical functioning in the Great Lakes region and elsewhere can alter system bioenergetics and promote harmful algal blooms.
23 Dec 17:28
Ensemble distribution models in conservation prioritization: from consensus predictions to consensus reserve networks
by Laura Meller, Mar Cabeza, Samuel Pironon, Morgane Barbet-Massin, Luigi Maiorano, Damien Georges, Wilfried Thuiller
Abstract
Aim
Conservation planning exercises increasingly rely on species distributions predicted either from one particular statistical model or, more recently, from an ensemble of models (i.e. ensemble forecasting). However, it has not yet been explored how different ways of summarizing ensemble predictions affect conservation planning outcomes. We evaluate these effects and compare commonplace consensus methods, applied before the conservation prioritization phase, to a novel method that applies consensus after reserve selection.
Location
Europe.
Methods
We used an ensemble of predicted distributions of 146 Western Palaearctic bird species in alternative ways: four different consensus methods, as well as distributions discounted with variability, were used to produce inputs for spatial conservation prioritization. In addition, we developed and tested a novel method, in which we built 100 datasets by sampling the ensemble of predicted distributions, ran a conservation prioritization analysis on each of them and averaged the resulting priority ranks. We evaluated the conservation outcome against three controls: (i) a null control, based on random ranking of cells; (2) the reference solution, based on an expert-refined dataset; and (3) the independent solution, based on an independent dataset.
Results
Networks based on predicted distributions were more representative of rare species than randomly selected networks. Alternative methods to summarize ensemble predictions differed in representativeness of resulting reserve networks. Our novel method resulted in better representation of rare species than pre-selection consensus methods.
Main conclusions
Retaining information about the variation in the predicted distributions throughout the conservation prioritization seems to provide better results than summarizing the predictions before conservation prioritization. Our results highlight the need to understand and consider model-based uncertainty when using predicted distribution data in conservation prioritization.
23 Dec 17:27
Diversity, distribution and conservation status of island conifers: a global review
by Beatriz Rumeu, Virginia Afonso, José María Fernández-Palacios, Manuel Nogales
Abstract
Aim
Conifers comprise an ancient and diverse group of plants showing a wide distribution range. To better understand the general patterns of species successfully established on islands, this review compiles information about the distribution, diversity, dispersal potential and conservation status of insular conifers, with special emphasis on those inhabiting remote oceanic islands.
Location
Global.
Methods
An exhaustive survey was made of world-wide databases and literature. We registered information on island distribution (including ocean region, extension and geological origin of the island), endemism and threat status for each insular conifer.
Results
285 of the 547 conifer species considered in this review show an insular distribution (i.e. their distribution encompass insular territories). The family Podocarpaceae is best represented, with 40% of the insular species. The importance of endozoochory for long-distance dispersal is clear, because it was the most frequent dispersal syndrome among oceanic conifers. A high proportion of the total threatened conifers occur on islands (52%), and many of them are insular endemics (72%). Among conifer families, Araucariaceae is the most threatened in insular territories.
Main conclusions
Our results highlight the wide diversity of insular conifers, as well as the key role of oceanic islands in catalysing speciation mechanisms. Pacific islands in particular harbour the greatest diversity levels, constituting a major centre of diversification. The wide distribution of conifers reflects their great potential for dispersal and colonization, endozoochory being the most favourable dispersal syndrome for reaching remote islands. The general threat status of insular conifers highlights the fragility of island biota and the urgent need for policies focused on their preservation.
23 Dec 17:27
MODULAR: software for the autonomous computation of modularity in large network sets
by Flavia Maria Darcie Marquitti, Paulo Roberto Guimarães, Mathias Mistretta Pires, Luiz Fernando Bittencourt
Many ecological systems can be represented as networks of interactions. A key feature in these networks is their organization into modules, which are subsets of tightly connected elements. We introduce MODULAR to perform rapid and autonomous calculation of modularity in network sets. MODULAR reads a set of files representing unipartite or bipartite networks, and identifies modules using two different modularity metrics widely used in the ecological networks literature. To estimate modularity, the software offers five optimization methods to the user. The software also includes two null models commonly used in studies of ecological networks to verify how the degree of modularity differs from two distinct theoretical benchmarks.
23 Dec 17:27
Invasion trajectory of alien trees: the role of introduction pathway and planting history
by Jason E. Donaldson, Cang Hui, David M. Richardson, Mark P. Robertson, Bruce L. Webber, John R. U. Wilson
Abstract
Global change is driving a massive rearrangement of the world's biota. Trajectories of distributional shifts are shaped by species traits, the recipient environment and driving forces with many of the driving forces directly due to human activities. The relative importance of each in determining the distributions of introduced species is poorly understood. We consider 11 Australian Acacia species introduced to South Africa for different reasons (commercial forestry, dune stabilization and ornamentation) to determine how features of the introduction pathway have shaped their invasion history. Projections from species distribution models (SDMs) were developed to assess how the reason for introduction influences the similarity between climatic envelopes in native and alien ranges. A lattice model for an idealized invasion was developed to assess the relative contribution of intrinsic traits and introduction dynamics on the abundance and extent over the course of simulated invasions. SDMs show that alien populations of ornamental species in South Africa occupy substantially different climate space from their native ranges, whereas species introduced for forestry occupy a similar climate space in native and introduced ranges. This may partly explain the slow spread rates observed for some alien ornamental plants. Such mismatches are likely to become less pronounced with the current drive towards ‘eco gardens’ resulting in more introductions of ornamental species with a close climate match between native and newly introduced regions. The results from the lattice model showed that the conditions associated with the introduction pathway (especially introduction pressure) dominate early invasion dynamics. The placement of introduction foci in urban areas limited the extent and abundance of invasive populations. Features of introduction events appear to initially mask the influence of intrinsic species traits on invasions and help to explain the relative success of species introduced for different purposes. Introduction dynamics therefore can have long-lasting influences on the outcomes of species redistributions, and must be explicitly considered in management plans.
10 Dec 19:40
Making better Maxent models of species distributions: complexity, overfitting and evaluation
by Aleksandar Radosavljevic, Robert P. Anderson
Abstract
Aim
Models of species niches and distributions have become invaluable to biogeographers over the past decade, yet several outstanding methodological issues remain. Here we address three critical ones: selecting appropriate evaluation data, detecting overfitting, and tuning program settings to approximate optimal model complexity. We integrate solutions to these issues for Maxent models, using the Caribbean spiny pocket mouse, Heteromys anomalus, as an example.
Location
North-western South America.
Methods
We partitioned data into calibration and evaluation datasets via three variations of k-fold cross-validation: randomly partitioned, geographically structured and masked geographically structured (which restricts background data to regions corresponding to calibration localities). Then, we carried out tuning experiments by varying the level of regularization, which controls model complexity. Finally, we gauged performance by quantifying discriminatory ability and overfitting, as well as via visual inspections of maps of the predictions in geography.
Results
Performance varied among data-partitioning approaches and among regularization multipliers. The randomly partitioned approach inflated estimates of model performance and the geographically structured approach showed high overfitting. In contrast, the masked geographically structured approach allowed selection of high-performing models based on all criteria. Discriminatory ability showed a slight peak in performance around the default regularization multiplier. However, regularization levels two to four times higher than the default yielded substantially lower overfitting. Visual inspection of maps of model predictions coincided with the quantitative evaluations.
Main conclusions
Species-specific tuning of model parameters can improve the performance of Maxent models. Further, accurate estimates of model performance and overfitting depend on using independent evaluation data. These strategies for model evaluation may be useful for other modelling methods as well.
10 Dec 19:40
The biodiversity data knowledge gap: Assessing information loss in the management of Biosphere Reserves
Publication date: May 2014
Source:Biological Conservation, Volume 173
Author(s): Andrea Pino-Del-Carpio , Arturo H. Ariño , Ana Villarroya , Jordi Puig , Rafael Miranda
The knowledge of biodiversity within an area is vital if we want to develop adequate conservation strategies. Biosphere Reserves are purposefully established for the sustainable use of their resources, and therefore their biodiversity should be well known. We compared and evaluated information available for Mexican Biosphere Reserves on threatened and non-threatened vertebrate species records from three different sources – the corresponding Biosphere Reserves management plans (MPs), the Global Biodiversity Information Facility index (GBIF), and scientific literature, in order to find potential knowledge gaps. Our results suggest that there were varying gaps in information among sources according to vertebrate group. For each group of vertebrate species, management plans held the largest subsets of information but were not complete, ranging from 89.6% of the combined known species of birds to 70% for amphibians and freshwater fishes. However, both GBIF and literature included data absent from MPs, and GBIF included data not otherwise available, proving it as important as literature or other data sources (e.g. field data) used for crafting such plans. Moreover, we found references to threatened species that were not listed in the MPs, reaching to as many as 50% of the total known species of fish. Species information shared by all three sources ranged from 28% for amphibians to 72.5% for birds. Conservation efforts should therefore take into account that possibly less charismatic taxa such as amphibians, reptiles and freshwater fish lack more information than birds or mammals. The disparity observed in the vertebrate species information constitutes an information gap that could (or should) be solved by scientists and managers alike.
Source:Biological Conservation, Volume 173
Author(s): Andrea Pino-Del-Carpio , Arturo H. Ariño , Ana Villarroya , Jordi Puig , Rafael Miranda
The knowledge of biodiversity within an area is vital if we want to develop adequate conservation strategies. Biosphere Reserves are purposefully established for the sustainable use of their resources, and therefore their biodiversity should be well known. We compared and evaluated information available for Mexican Biosphere Reserves on threatened and non-threatened vertebrate species records from three different sources – the corresponding Biosphere Reserves management plans (MPs), the Global Biodiversity Information Facility index (GBIF), and scientific literature, in order to find potential knowledge gaps. Our results suggest that there were varying gaps in information among sources according to vertebrate group. For each group of vertebrate species, management plans held the largest subsets of information but were not complete, ranging from 89.6% of the combined known species of birds to 70% for amphibians and freshwater fishes. However, both GBIF and literature included data absent from MPs, and GBIF included data not otherwise available, proving it as important as literature or other data sources (e.g. field data) used for crafting such plans. Moreover, we found references to threatened species that were not listed in the MPs, reaching to as many as 50% of the total known species of fish. Species information shared by all three sources ranged from 28% for amphibians to 72.5% for birds. Conservation efforts should therefore take into account that possibly less charismatic taxa such as amphibians, reptiles and freshwater fish lack more information than birds or mammals. The disparity observed in the vertebrate species information constitutes an information gap that could (or should) be solved by scientists and managers alike.
05 Dec 23:12
Ecosystem services ant communities
by Wielgoss, A., Tscharntke, T., Rumede, A., Fiala, B., Seidel, H., Shahabuddin, S., Clough, Y.
Owing to complex direct and indirect effects, impacts of higher trophic levels on plants is poorly understood. In tropical agroecosystems, ants interact with crop mutualists and antagonists, but little is known about how this integrates into the final ecosystem service, crop yield. We combined ant exclusion and introduction of invasive and native-dominant species in cacao agroecosystems to test whether (i) ant exclusion reduces yield, (ii) dominant species maximize certain intermediate ecosystem services (e.g. control of specific pests) rather than yield, which depends on several, cascading intermediate services and (iii) even, species-rich ant communities result in highest yields. Ants provided services, including reduced leaf herbivory and fruit pest damage and indirect pollination facilitation, but also disservices, such as increased mealybug density, phytopathogen dissemination and indirect pest damage enhancement. Yields were highest with unmanipulated, species-rich, even communities, whereas ant exclusion decreased yield by 27%. Introduction of an invasive-dominant ant decreased species density and evenness and resulted in 34% lower yields, whereas introduction of a non-invasive-dominant species resulted in similar species density and yields as in the unmanipulated control. Species traits and ant community structure affect services and disservices for agriculture in surprisingly complex ways, with species-rich and even communities promoting highest yield.
05 Dec 23:12
Global and regional nested patterns of non-native invasive floras on tropical islands
by Anna Traveset, Christoph Kueffer, Curtis C. Daehler
Abstract
Aim
Non-native species are being distributed globally as a result of human actions, but we still know little about emerging biogeographical patterns. We tested whether the distribution of plant invaders across tropical oceanic islands has a nested structure, and identified mechanisms to explain nestedness among invaders and islands.
Location
Tropical islands world-wide.
Methods
We analysed two datasets: a global one (350 spermatophyte species invading natural areas within 25 archipelagos) and a regional one (145 species within 12 Pacific archipelagos). We quantified island and species nestedness using the NODF metric and evaluated the contributions of each island and species to nestedness.
Results
Globally, the distribution of invaders across islands showed a nested pattern related to island area, elevation (a proxy of habitat diversity) and invasive species richness; the pattern was weakly associated with human population density and independent of isolation from the nearest continent. Invader prevalence among islands was the best predictor of species nestedness. Nestedness was more pronounced at a regional than a global scale.
Main conclusions
We found novel biogeographical patterns interconnecting non-native invasive floras at a global scale. Both localized and widespread species are important components of island invasive floras. Invader-rich islands host many rare invaders, and many species are invaders in only one island group, suggesting that prevention efforts should pay attention to rare invaders. We have developed a conceptual model to facilitate understanding of nestedness in island invasion. Both habitat and dispersal filtering are potential mechanisms underlying nestedness, whereas idiosyncratic factors of particular islands (e.g. habitat diversity and socio-economic history) or time-lags may explain ‘invader endemicity'. Nested regional patterns may be explained by ‘hub' islands that serve as early sites of introduction for many invaders, some of which subsequently spread across the region.
05 Dec 23:11
Morphological characteristics of urban water bodies: mechanisms of change and implications for ecosystem function
by onlinepublishing@allenpress.com (Meredith K. Steele et al)
Ecological Applications, Volume 24, Issue 5, Page 1070-1084, July 2014.
The size, shape, and connectivity of water bodies (lakes, ponds, and wetlands) can have important effects on ecological communities and ecosystem processes, but how these characteristics are influenced by land use and land cover change over broad spatial scales is not known. Intensive alteration of water bodies during urban development, including construction, burial, drainage, and reshaping, may select for certain morphometric characteristics and influence the types of water bodies present in cities. We used a database of over one million water bodies in 100 cities across the conterminous United States to compare the size distributions, connectivity (as intersection with surface flow lines), and shape (as measured by shoreline development factor) of water bodies in different land cover classes. Water bodies in all urban land covers were dominated by lakes and ponds, while reservoirs and wetlands comprised only a small fraction of the sample. In urban land covers, as compared to surrounding undeveloped land, water body size distributions converged on moderate sizes, shapes toward less tortuous shorelines, and the number and area of water bodies that intersected surface flow lines (i.e., streams and rivers) decreased. Potential mechanisms responsible for changing the characteristics of urban water bodies include: preferential removal, physical reshaping or addition of water bodies, and selection of locations for development. The relative contributions of each mechanism likely change as cities grow. The larger size and reduced surface connectivity of urban water bodies may affect the role of internal dynamics and sensitivity to catchment processes. More broadly, these results illustrate the complex nature of urban watersheds and highlight the need to develop a conceptual framework for urban water bodies.
The size, shape, and connectivity of water bodies (lakes, ponds, and wetlands) can have important effects on ecological communities and ecosystem processes, but how these characteristics are influenced by land use and land cover change over broad spatial scales is not known. Intensive alteration of water bodies during urban development, including construction, burial, drainage, and reshaping, may select for certain morphometric characteristics and influence the types of water bodies present in cities. We used a database of over one million water bodies in 100 cities across the conterminous United States to compare the size distributions, connectivity (as intersection with surface flow lines), and shape (as measured by shoreline development factor) of water bodies in different land cover classes. Water bodies in all urban land covers were dominated by lakes and ponds, while reservoirs and wetlands comprised only a small fraction of the sample. In urban land covers, as compared to surrounding undeveloped land, water body size distributions converged on moderate sizes, shapes toward less tortuous shorelines, and the number and area of water bodies that intersected surface flow lines (i.e., streams and rivers) decreased. Potential mechanisms responsible for changing the characteristics of urban water bodies include: preferential removal, physical reshaping or addition of water bodies, and selection of locations for development. The relative contributions of each mechanism likely change as cities grow. The larger size and reduced surface connectivity of urban water bodies may affect the role of internal dynamics and sensitivity to catchment processes. More broadly, these results illustrate the complex nature of urban watersheds and highlight the need to develop a conceptual framework for urban water bodies.