Climate concerns and the disabled community Climate change and the loss of ecosystem services are... more Climate concerns and the disabled community Climate change and the loss of ecosystem services are likely to disproportionately affect the world's disabled populations by Students in the University of Washington's "DO-IT" Scholars program discuss data with an instructor.
As the influence of climate change on tropical forests becomes apparent, more studies are needed ... more As the influence of climate change on tropical forests becomes apparent, more studies are needed to understand how changes in climatic variables such as rainfall are likely to affect tree phenology. Using a twelve‐year dataset (2005–2016), we studied the impact of seasonal rainfall patterns on the fruiting phenology of 69 tree species in the rain forest of southeastern Madagascar. We found that average annual rainfall in this region has increased by >800 mm (23%) during this period relative to that recorded for the previous 40 years and was highly variable both within and between years. Higher monthly measures of fruiting richness and the intensity of fruiting in our sample community were associated with significantly higher levels of rainfall. We also found that less rainfall during the dry season, but not the wet season, was associated with a significant shift toward later timing of peak richness and peak intensity of fruiting in the subsequent 12 months; however, this pattern ...
Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tro... more Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tropical forests. Previous work has suggested that loss of seed dispersal by large frugivores may have a negative impact on ecosystem carbon storage by reducing tree biomass. However, we know little about the potential impacts of losing frugivores in Madagascar's diverse rainforest ecosystem. Understanding the effects of frugivore extinction on carbon loss is relevant in Madagascar, where threatened lemur taxa are the only dispersers of many large-seeded plant species. Using a dataset of tree species composition and traits from the southeastern rainforests of Ranomafana National Park, we examined whether seed size and lemur-dependent dispersal are positively associated with above-ground tree biomass. We then simulated different scenarios of population declines of large-seeded trees (>10 mm seed length) dependent on lemur-mediated seed dispersal, to examine potential directional changes in carbon storage capacity of Malagasy forests under lemur loss. Lemur-dispersed tree species, which have large seeds, had higher above-ground biomass than other species. Our simulations showed that the loss of large frugivorous primates in Madagascar may decrease the forest's potential to store carbon. These results demonstrate the importance Int J Primatol
Primate seed dispersal is a vital, but complex, ecological process that involves many interacting... more Primate seed dispersal is a vital, but complex, ecological process that involves many interacting agents and plays important roles in the maintenance of old-growth forest, as well as in the development of regenerating forest. Focusing primarily on African examples, in this article we briefly review the ecological process of primate seed dispersal, highlighting understudied and contentious topics, and then we discuss how our knowledge on primate seed dispersal can promote both forest restoration and primate conservation. Though it is frequently claimed that primates are critically important for the maintenance of diverse tropical forest ecosystems, we believe that more empirical evidence is needed to support this claim. Confounding factors can often be difficult to rule out and long-term studies extending beyond the seedling or sapling stage are very rare. In addition, though primates are critical for initial seed dispersal of many tree species, spatial and temporal variation in postdeposition processes, such as secondary seed dispersal and predation by rodents, can dramatically alter the initial patterns generated by primates. However, given the need for immediate conservation action to prevent further primate extinctions, we advocate that the knowledge about primate seed dispersal be used in formulating informed conservation plans. One prominent area where this knowledge will prove extremely valuable is in forest restoration efforts. To aid in the development of such efforts, we
Proceedings of the National Academy of Sciences of the United States of America, Oct 28, 2017
Dispersal is thought to be a key process underlying the high spatial diversity of tropical forest... more Dispersal is thought to be a key process underlying the high spatial diversity of tropical forests. Just how important dispersal is in structuring plant communities is nevertheless an open question because it is very difficult to isolate dispersal from other processes, and thereby measure its effect. Using a unique situation, the loss of vertebrate seed dispersers on the island of Guam and their presence on the neighboring islands of Saipan and Rota, we quantify the contribution of vertebrate seed dispersal to spatial patterns of diversity of tree seedlings in treefall gaps. The presence of vertebrate seed dispersers approximately doubled seedling species richness within canopy gaps and halved species turnover among gaps. Our study demonstrates that dispersal plays a key role in maintaining local and regional patterns of diversity, and highlights the potential for ongoing declines in vertebrate seed dispersers to profoundly alter tropical forest composition.
Summary Co‐fruiting plant species are subject to a variety of biotic and abiotic processes that m... more Summary Co‐fruiting plant species are subject to a variety of biotic and abiotic processes that may influence patterns of fruiting phenology and the functional and phylogenetic diversity of co‐fruiting taxa in a community. Understanding the seasonal patterns of functional and phylogenetic diversity of fruiting in a community will shed new light on potential mechanisms structuring plant communities. Using rain forest trees in south‐eastern Madagascar as our system, we predicted there would be clustering of fruit and seed traits and phylogenetic relationships among co‐fruiting species because plants are vying for seed‐dispersal services from a limited set of generalist frugivore taxa. We also predicted that seasonal variations in rainfall would mediate fluctuations in functional trait and phylogenetic diversity of co‐fruiting assemblages. Despite fluctuating patterns in their functional trait diversity over time, co‐fruiting assemblages displayed consistent clustering of fruit/seed tr...
Frugivores are the main seed dispersers in many ecosystems, such that behaviorally driven, nonran... more Frugivores are the main seed dispersers in many ecosystems, such that behaviorally driven, nonrandom patterns of seed dispersal are a common process; but patterns are poorly understood. Characterizing these patterns may be essential for understanding spatial organization of fruiting trees and drivers of seed-dispersal limitation in biodiverse forests. To address this, we studied resulting spatial associations between dispersed seeds and adult tree neighbors in a diverse rainforest in Madagascar, using a temporal and phylogenetic approach. Data show that by using fruiting trees as seed-dispersal foci, frugivores bias seed dispersal under conspecific adults and under heterospecific trees that share dispersers and fruiting time with the dispersed species. Frugivore-mediated seed dispersal also resulted in nonrandom phylogenetic associations of dispersed seeds with their nearest adult neighbors, in nine out of the 16 months of our study. However, these nonrandom phylogenetic associations fluctuated unpredictably over time, ranging from clustered to overdispersed. The spatial and phylogenetic template of seed dispersal did not translate to similar patterns of association in adult tree neighborhoods, suggesting the importance of post-dispersal processes in structuring plant communities. Results suggest that frugivoremediated seed dispersal is important for structuring early stages of plant-plant associations, setting the template for post-dispersal processes that influence ultimate patterns of plant recruitment. Importantly, if biased patterns of dispersal are common in other systems, frugivores may promote tree coexistence in biodiverse forests by limiting the frequency and diversity of heterospecific interactions of seeds they disperse.
The accumulation of seeds in the soil (the seedbank) can set the template for the early regenerat... more The accumulation of seeds in the soil (the seedbank) can set the template for the early regeneration of habitats following disturbance. Seed dispersal is an important factor determining the pattern of seed rain, which affects the interactions those seeds experience. For this reason, seed dispersal should play an important role in structuring forest seedbanks, yet we know little about how that happens. Using the functional extirpation of frugivorous vertebrates from the island of Guam, together with two nearby islands (Saipan and Rota) that each support relatively intact disperser assemblages, we aimed to identify the role of vertebrate dispersers in structuring forest seedbanks. We sampled the seedbank on Guam where dispersers are absent, and compared this with the seedbank on Saipan and Rota where they are present. Almost twice as many species found in the seedbank on Guam, when compared with Saipan and Rota, had a conspecific adult within 2 m. This indicates a strong role of vertebrate dispersal in determining the identity of seeds in the seedbank. In addition, on Guam, a greater proportion of samples contained no seeds and overall species richness was lower than on Saipan. Differences in seed abundance and richness between Guam and Rota were less clear, as seedbanks on Rota also contained fewer species than Saipan, possibly due to increased post-dispersal seed predation. Our findings suggest that vertebrate seed dispersers can have a strong influence on the species composition of seedbanks. Regardless of post-dispersal processes, without dispersal, seedbanks no longer serve to increase the species pool of recruits during regeneration.
Ex situ populations play a critical role for the conservation of endangered species, especially w... more Ex situ populations play a critical role for the conservation of endangered species, especially where in situ populations face imminent threats. For such populations to act as vital reserves, they must be viable and sustainable. Eastern black rhinoceros (Diceros bicornis michaeli) epitomise the delicate nature of conservation, as a steady increase in the in situ population over the last two decades is threatened to reverse due to intense poaching pressures on rhinoceros across sub-Saharan Africa. This study utilized population viability analysis to evaluate the demographic and genetic viability of the European captive population of eastern black rhinoceros, and compared demographic parameters to in situ reference populations. Although self-sustaining, the ex situ population performs poorly relative to in situ counterparts, growing at a rate of only 1-2 % per annum compared to 6-8 % for managed wild populations. Captive females start reproducing later, have longer inter-calving intervals, and a lower proportion breed each year. Furthermore, over 40 % of reproductive-age animals have yet to reproduce, with additional implications for the maintenance of genetic diversity. Pedigree analysis highlights the unequal contribution of wild-caught founders to the current population; 69 % of which have no living descendants, and more than a third of the current population are related to five founders. This results in a current genome equivalent of just 13.39 equally reproducing founders. Although Communicated by Simon Ingram.
Background/Question/Methods Predicting which species are likely to become invaders in a given env... more Background/Question/Methods Predicting which species are likely to become invaders in a given environment has been a central challenge in ecology and conservation biology. Invasive species can have large ecological and economic costs, thus understanding what makes an exotic species a successful invader has global significance for managing ecosystems as well as important theoretical implications for understanding community assembly. Many current approaches seek to predict successful invaders by examining the traits of introduced taxa or habitat characteristics. However, recent studies have suggested that phylogenetic relationships between potential invaders and the native community may offer better predictions of likely invaders in a given community. This approach has proven successful in multiple studies, but has thus far predominantly been tested on plants. In order to determine if this method is more broadly applicable, we tested it on two highly invaded vertebrate communities, th...
Bulletin of the Ecological Society of America, 2015
We investigated the advantages of directed dispersal by multiple frugivores to plant recruitment.... more We investigated the advantages of directed dispersal by multiple frugivores to plant recruitment. We used probability recruitment models of a long-lived rain forest tree in Madagascar, to compare recruitment success with dispersal by multiple frugivorous lemurs, with no dispersal, and random dispersal. Our results show that frugivore-mediated seed dispersal was nonrandom with respect to canopy cover and increased modeled per-seed sapling recruitment fourfold compared to no dispersal. Seeds dispersed by one frugivore, Eulemur rubriventer, had higher modeled recruitment probability than seeds dispersed randomly. However, as a group, our models suggest that seeds dispersed by lemurs would have lower recruitment than if dispersal were random. Onja H. Razafindratsima and Amy E. Dunham
Directed dispersal is defined as enhanced dispersal of seeds into suitable microhabitats, resulti... more Directed dispersal is defined as enhanced dispersal of seeds into suitable microhabitats, resulting in higher recruitment than if seeds were dispersed randomly. While this constitutes one of the main explanations for the adaptive value of frugivore‐mediated seed dispersal, the generality of this advantage has received little study, particularly when multiple dispersers are involved. We used probability recruitment models of a long‐lived rainforest tree in Madagascar to compare recruitment success under dispersal by multiple frugivores, no dispersal, and random dispersal. Models were parameterized using a three‐year recruitment experiment and observational data of dispersal events by three frugivorous lemur species that commonly disperse its seeds. Frugivore‐mediated seed dispersal was nonrandom with respect to canopy cover and increased modeled per‐seed sapling recruitment fourfold compared to no dispersal. Seeds dispersed by one frugivore, Eulemur rubriventer, had higher modeled re...
Proceedings of the Royal Society B: Biological Sciences, 2012
Understanding what traits determine the extinction risk of species has been a long-standing chall... more Understanding what traits determine the extinction risk of species has been a long-standing challenge. Natural populations increasingly experience reductions in habitat and population size concurrent with increasing novel environmental variation owing to anthropogenic disturbance and climate change. Recent studies show that a species risk of decline towards extinction is often non-random across species with different life histories. We propose that species with life histories in which all stage-specific vital rates are more evenly important to population growth rate may be less likely to decline towards extinction under these pressures. To test our prediction, we modelled declines in population growth rates under simulated stochastic disturbance to the vital rates of 105 species taken from the literature. Populations with more equally important vital rates, determined using elasticity analysis, declined more slowly across a gradient of increasing simulated environmental variation. F...
Understanding the impact of losing trophic diversity has global significance for managing ecosyst... more Understanding the impact of losing trophic diversity has global significance for managing ecosystems as well as important theoretical implications for community and ecosystem ecology. In several tropical forest ecosystems, habitat fragmentation has resulted in declines and local extinctions of mammalian and avian terrestrial insectivores. To assess the ability of a tropical rainforest community in Ivory Coast to resist perturbation from such loss of trophic diversity, I traced feedbacks in above and below ground communities and measured changes in nutrient levels and herbivory rates in response to an experimental exclosure of avian and mammalian terrestrial insectivores. I present evidence that loss of this functional group may result in increased tree seedling herbivory and altered nutrient regimes through changes in the abundance and guild structure of invertebrates. Exclusion of top predators of the forest floor resulted in increased seedling herbivory rates and macro‐invertebrat...
Biopedturbation, or animal-caused soil disturbance, may be important for development and maintena... more Biopedturbation, or animal-caused soil disturbance, may be important for development and maintenance of small-scale heterogeneity in ecosystems with the potential to alter seed mortality and recruitment. However, its role in tropical forests has been largely ignored. This study explored effects of vertebrate biopedturbation on seed (1) microsite heterogeneity, (2) predation and (3) germination in a West African rain forest. Exclosure experiments were used to study how biopedturbation altered burial and movements of seeds of four common canopy species. Effect of seed burial on removal by seed predators was also examined. Germination of the dominant canopy species (Raphia palma-pinus) in swamp forest was tested within artificial disturbances mimicking that of a locally common but endangered mammal, the Liberian mongoose (Liberiictis kuhni), which was estimated to turn over the entire forest floor in this habitat in c. 8 mo. Seed exposure to biopedturbation for 20 d (n = 80) led to an overall 6.5-fold increase in small-scale horizontal movement and increased probability of burial (6-52% higher), varying by species. Burial effectively eliminated seed removal for all four species (n = 160) by seed predators over 20 d. Germination of Raphia palma-pinus seeds (n = 100) was enhanced by 17.5% on average over 4 mo in simulated disturbances. Results suggest biopedturbation may be important for seedling recruitment and that loss of species with this functional role could have underappreciated yet important impacts on tropical plant communities.
Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating ... more Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating the strategies and structures by which natural communities of species persist remains a challenge to empirical and theoretical ecologists. We show that simple regulatory feedbacks between autotrophs and their environment when embedded within complex and realistic food-web models enhance biodiversity. The food webs are generated through the niche-model algorithm and coupled with predator-prey dynamics, with and without environmental feedbacks at the autotroph level. With high probability and especially at lower, more realistic connectance levels, regulatory environmental feedbacks result in fewer species extinctions, that is, in increased species persistence. These same feedback couplings, however, also sensitize food webs to environmental stresses leading to abrupt collapses in biodiversity with increased forcing. Feedback interactions between species and their material environments anchor food-web persistence, adding another dimension to biodiversity conservation. We suggest that the regulatory features of two natural systems, deep-sea tubeworms with their microbial consortia and a soil ecosystem manifesting adaptive homeostatic changes, can be embedded within niche-model food-web dynamics.
Understanding the evolution of body size and sexual size dimorphism has been a longstanding goal ... more Understanding the evolution of body size and sexual size dimorphism has been a longstanding goal in evolutionary biology. Previous work has shown that environmental stress can constrain male-biased sexual size dimorphism at the population level, but we know little about how this might translate to geographical patterns of body size and sexual size dimorphism at the species level. Environmental constraints due to a highly seasonal, resource-poor and/or variable environment have often been cited to explain the unusual lack of sexual size dimorphism among Madagascar's diverse and numerous primate taxa; however, empirical tests of this hypothesis are lacking. Using a phylogenetic approach and a geographical information system platform, we explored the role of seasonality, interannual variability and annual measures of temperature and rainfall, and net primary productivity on patterns of body size and sexual size dimorphism across 130 species of primates. Phylogenetically controlled comparisons showed no support for a role of environmental constraints in moderating sexual size dimorphism at the interspecific level, despite significant associations of environmental variables with body mass. Results suggest that the focus of discussions that have dominated in the last two decades regarding the role of environmental constraints in driving patterns of monomorphism of Madagascar's lemurs should be reconsidered; however, the conundrum remains.
Most studies that examine the influence of climatic change on flora and fauna have focused on nor... more Most studies that examine the influence of climatic change on flora and fauna have focused on northern latitudes; however, there is increasing recognition that tropical regions are also being affected. Despite this, regions such as Madagascar, which are rich in endemic biodiversity but may have low adaptive capacity to climatic change, are poorly represented in studies examining the effects of climate variability on biota. We investigated how El Niñ o Southern Oscillations (ENSO) influence precipitation patterns in the rainforest region of southeastern Madagascar (1962-2006) and then constructed models to assess the potential contribution of climatic variables on the reproductive parameters of the Milne Edward's sifaka, a threatened lemur species (Propithecus edwardsi), over a 20-year period. The Southern Oscillation Index of sea surface temperature (SST) anomalies in the tropical Pacific was associated with precipitation patterns including wetter wet seasons during warmer phases and drier dry seasons following cooler phases. The bestsupported models of lemur fecundity (female offspring per female that survive to 1 year of age per year) included cyclone presence during gestation and ENSO phase before conception and during the first 6 months of life. Models also suggested that heavy rains during gestation may limit birth rates and that prolonged drought during female lactation may limit first year offspring survival; although these variables were given little importance for predicting overall fecundity relative to ENSO phases and cyclone presence. Our results linking lemur reproduction with climatic variability suggest that climatic changes may be an additional threat to Madagascar's unique and already endangered flora and fauna. The association between precipitation in southeastern Madagascar and SST anomalies in the tropical Pacific suggests that dynamics of wildlife populations even in tropical areas such as Madagascar can be affected by global climate cycles making them potentially vulnerable to global climate change.
Climate concerns and the disabled community Climate change and the loss of ecosystem services are... more Climate concerns and the disabled community Climate change and the loss of ecosystem services are likely to disproportionately affect the world's disabled populations by Students in the University of Washington's "DO-IT" Scholars program discuss data with an instructor.
As the influence of climate change on tropical forests becomes apparent, more studies are needed ... more As the influence of climate change on tropical forests becomes apparent, more studies are needed to understand how changes in climatic variables such as rainfall are likely to affect tree phenology. Using a twelve‐year dataset (2005–2016), we studied the impact of seasonal rainfall patterns on the fruiting phenology of 69 tree species in the rain forest of southeastern Madagascar. We found that average annual rainfall in this region has increased by >800 mm (23%) during this period relative to that recorded for the previous 40 years and was highly variable both within and between years. Higher monthly measures of fruiting richness and the intensity of fruiting in our sample community were associated with significantly higher levels of rainfall. We also found that less rainfall during the dry season, but not the wet season, was associated with a significant shift toward later timing of peak richness and peak intensity of fruiting in the subsequent 12 months; however, this pattern ...
Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tro... more Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tropical forests. Previous work has suggested that loss of seed dispersal by large frugivores may have a negative impact on ecosystem carbon storage by reducing tree biomass. However, we know little about the potential impacts of losing frugivores in Madagascar's diverse rainforest ecosystem. Understanding the effects of frugivore extinction on carbon loss is relevant in Madagascar, where threatened lemur taxa are the only dispersers of many large-seeded plant species. Using a dataset of tree species composition and traits from the southeastern rainforests of Ranomafana National Park, we examined whether seed size and lemur-dependent dispersal are positively associated with above-ground tree biomass. We then simulated different scenarios of population declines of large-seeded trees (>10 mm seed length) dependent on lemur-mediated seed dispersal, to examine potential directional changes in carbon storage capacity of Malagasy forests under lemur loss. Lemur-dispersed tree species, which have large seeds, had higher above-ground biomass than other species. Our simulations showed that the loss of large frugivorous primates in Madagascar may decrease the forest's potential to store carbon. These results demonstrate the importance Int J Primatol
Primate seed dispersal is a vital, but complex, ecological process that involves many interacting... more Primate seed dispersal is a vital, but complex, ecological process that involves many interacting agents and plays important roles in the maintenance of old-growth forest, as well as in the development of regenerating forest. Focusing primarily on African examples, in this article we briefly review the ecological process of primate seed dispersal, highlighting understudied and contentious topics, and then we discuss how our knowledge on primate seed dispersal can promote both forest restoration and primate conservation. Though it is frequently claimed that primates are critically important for the maintenance of diverse tropical forest ecosystems, we believe that more empirical evidence is needed to support this claim. Confounding factors can often be difficult to rule out and long-term studies extending beyond the seedling or sapling stage are very rare. In addition, though primates are critical for initial seed dispersal of many tree species, spatial and temporal variation in postdeposition processes, such as secondary seed dispersal and predation by rodents, can dramatically alter the initial patterns generated by primates. However, given the need for immediate conservation action to prevent further primate extinctions, we advocate that the knowledge about primate seed dispersal be used in formulating informed conservation plans. One prominent area where this knowledge will prove extremely valuable is in forest restoration efforts. To aid in the development of such efforts, we
Proceedings of the National Academy of Sciences of the United States of America, Oct 28, 2017
Dispersal is thought to be a key process underlying the high spatial diversity of tropical forest... more Dispersal is thought to be a key process underlying the high spatial diversity of tropical forests. Just how important dispersal is in structuring plant communities is nevertheless an open question because it is very difficult to isolate dispersal from other processes, and thereby measure its effect. Using a unique situation, the loss of vertebrate seed dispersers on the island of Guam and their presence on the neighboring islands of Saipan and Rota, we quantify the contribution of vertebrate seed dispersal to spatial patterns of diversity of tree seedlings in treefall gaps. The presence of vertebrate seed dispersers approximately doubled seedling species richness within canopy gaps and halved species turnover among gaps. Our study demonstrates that dispersal plays a key role in maintaining local and regional patterns of diversity, and highlights the potential for ongoing declines in vertebrate seed dispersers to profoundly alter tropical forest composition.
Summary Co‐fruiting plant species are subject to a variety of biotic and abiotic processes that m... more Summary Co‐fruiting plant species are subject to a variety of biotic and abiotic processes that may influence patterns of fruiting phenology and the functional and phylogenetic diversity of co‐fruiting taxa in a community. Understanding the seasonal patterns of functional and phylogenetic diversity of fruiting in a community will shed new light on potential mechanisms structuring plant communities. Using rain forest trees in south‐eastern Madagascar as our system, we predicted there would be clustering of fruit and seed traits and phylogenetic relationships among co‐fruiting species because plants are vying for seed‐dispersal services from a limited set of generalist frugivore taxa. We also predicted that seasonal variations in rainfall would mediate fluctuations in functional trait and phylogenetic diversity of co‐fruiting assemblages. Despite fluctuating patterns in their functional trait diversity over time, co‐fruiting assemblages displayed consistent clustering of fruit/seed tr...
Frugivores are the main seed dispersers in many ecosystems, such that behaviorally driven, nonran... more Frugivores are the main seed dispersers in many ecosystems, such that behaviorally driven, nonrandom patterns of seed dispersal are a common process; but patterns are poorly understood. Characterizing these patterns may be essential for understanding spatial organization of fruiting trees and drivers of seed-dispersal limitation in biodiverse forests. To address this, we studied resulting spatial associations between dispersed seeds and adult tree neighbors in a diverse rainforest in Madagascar, using a temporal and phylogenetic approach. Data show that by using fruiting trees as seed-dispersal foci, frugivores bias seed dispersal under conspecific adults and under heterospecific trees that share dispersers and fruiting time with the dispersed species. Frugivore-mediated seed dispersal also resulted in nonrandom phylogenetic associations of dispersed seeds with their nearest adult neighbors, in nine out of the 16 months of our study. However, these nonrandom phylogenetic associations fluctuated unpredictably over time, ranging from clustered to overdispersed. The spatial and phylogenetic template of seed dispersal did not translate to similar patterns of association in adult tree neighborhoods, suggesting the importance of post-dispersal processes in structuring plant communities. Results suggest that frugivoremediated seed dispersal is important for structuring early stages of plant-plant associations, setting the template for post-dispersal processes that influence ultimate patterns of plant recruitment. Importantly, if biased patterns of dispersal are common in other systems, frugivores may promote tree coexistence in biodiverse forests by limiting the frequency and diversity of heterospecific interactions of seeds they disperse.
The accumulation of seeds in the soil (the seedbank) can set the template for the early regenerat... more The accumulation of seeds in the soil (the seedbank) can set the template for the early regeneration of habitats following disturbance. Seed dispersal is an important factor determining the pattern of seed rain, which affects the interactions those seeds experience. For this reason, seed dispersal should play an important role in structuring forest seedbanks, yet we know little about how that happens. Using the functional extirpation of frugivorous vertebrates from the island of Guam, together with two nearby islands (Saipan and Rota) that each support relatively intact disperser assemblages, we aimed to identify the role of vertebrate dispersers in structuring forest seedbanks. We sampled the seedbank on Guam where dispersers are absent, and compared this with the seedbank on Saipan and Rota where they are present. Almost twice as many species found in the seedbank on Guam, when compared with Saipan and Rota, had a conspecific adult within 2 m. This indicates a strong role of vertebrate dispersal in determining the identity of seeds in the seedbank. In addition, on Guam, a greater proportion of samples contained no seeds and overall species richness was lower than on Saipan. Differences in seed abundance and richness between Guam and Rota were less clear, as seedbanks on Rota also contained fewer species than Saipan, possibly due to increased post-dispersal seed predation. Our findings suggest that vertebrate seed dispersers can have a strong influence on the species composition of seedbanks. Regardless of post-dispersal processes, without dispersal, seedbanks no longer serve to increase the species pool of recruits during regeneration.
Ex situ populations play a critical role for the conservation of endangered species, especially w... more Ex situ populations play a critical role for the conservation of endangered species, especially where in situ populations face imminent threats. For such populations to act as vital reserves, they must be viable and sustainable. Eastern black rhinoceros (Diceros bicornis michaeli) epitomise the delicate nature of conservation, as a steady increase in the in situ population over the last two decades is threatened to reverse due to intense poaching pressures on rhinoceros across sub-Saharan Africa. This study utilized population viability analysis to evaluate the demographic and genetic viability of the European captive population of eastern black rhinoceros, and compared demographic parameters to in situ reference populations. Although self-sustaining, the ex situ population performs poorly relative to in situ counterparts, growing at a rate of only 1-2 % per annum compared to 6-8 % for managed wild populations. Captive females start reproducing later, have longer inter-calving intervals, and a lower proportion breed each year. Furthermore, over 40 % of reproductive-age animals have yet to reproduce, with additional implications for the maintenance of genetic diversity. Pedigree analysis highlights the unequal contribution of wild-caught founders to the current population; 69 % of which have no living descendants, and more than a third of the current population are related to five founders. This results in a current genome equivalent of just 13.39 equally reproducing founders. Although Communicated by Simon Ingram.
Background/Question/Methods Predicting which species are likely to become invaders in a given env... more Background/Question/Methods Predicting which species are likely to become invaders in a given environment has been a central challenge in ecology and conservation biology. Invasive species can have large ecological and economic costs, thus understanding what makes an exotic species a successful invader has global significance for managing ecosystems as well as important theoretical implications for understanding community assembly. Many current approaches seek to predict successful invaders by examining the traits of introduced taxa or habitat characteristics. However, recent studies have suggested that phylogenetic relationships between potential invaders and the native community may offer better predictions of likely invaders in a given community. This approach has proven successful in multiple studies, but has thus far predominantly been tested on plants. In order to determine if this method is more broadly applicable, we tested it on two highly invaded vertebrate communities, th...
Bulletin of the Ecological Society of America, 2015
We investigated the advantages of directed dispersal by multiple frugivores to plant recruitment.... more We investigated the advantages of directed dispersal by multiple frugivores to plant recruitment. We used probability recruitment models of a long-lived rain forest tree in Madagascar, to compare recruitment success with dispersal by multiple frugivorous lemurs, with no dispersal, and random dispersal. Our results show that frugivore-mediated seed dispersal was nonrandom with respect to canopy cover and increased modeled per-seed sapling recruitment fourfold compared to no dispersal. Seeds dispersed by one frugivore, Eulemur rubriventer, had higher modeled recruitment probability than seeds dispersed randomly. However, as a group, our models suggest that seeds dispersed by lemurs would have lower recruitment than if dispersal were random. Onja H. Razafindratsima and Amy E. Dunham
Directed dispersal is defined as enhanced dispersal of seeds into suitable microhabitats, resulti... more Directed dispersal is defined as enhanced dispersal of seeds into suitable microhabitats, resulting in higher recruitment than if seeds were dispersed randomly. While this constitutes one of the main explanations for the adaptive value of frugivore‐mediated seed dispersal, the generality of this advantage has received little study, particularly when multiple dispersers are involved. We used probability recruitment models of a long‐lived rainforest tree in Madagascar to compare recruitment success under dispersal by multiple frugivores, no dispersal, and random dispersal. Models were parameterized using a three‐year recruitment experiment and observational data of dispersal events by three frugivorous lemur species that commonly disperse its seeds. Frugivore‐mediated seed dispersal was nonrandom with respect to canopy cover and increased modeled per‐seed sapling recruitment fourfold compared to no dispersal. Seeds dispersed by one frugivore, Eulemur rubriventer, had higher modeled re...
Proceedings of the Royal Society B: Biological Sciences, 2012
Understanding what traits determine the extinction risk of species has been a long-standing chall... more Understanding what traits determine the extinction risk of species has been a long-standing challenge. Natural populations increasingly experience reductions in habitat and population size concurrent with increasing novel environmental variation owing to anthropogenic disturbance and climate change. Recent studies show that a species risk of decline towards extinction is often non-random across species with different life histories. We propose that species with life histories in which all stage-specific vital rates are more evenly important to population growth rate may be less likely to decline towards extinction under these pressures. To test our prediction, we modelled declines in population growth rates under simulated stochastic disturbance to the vital rates of 105 species taken from the literature. Populations with more equally important vital rates, determined using elasticity analysis, declined more slowly across a gradient of increasing simulated environmental variation. F...
Understanding the impact of losing trophic diversity has global significance for managing ecosyst... more Understanding the impact of losing trophic diversity has global significance for managing ecosystems as well as important theoretical implications for community and ecosystem ecology. In several tropical forest ecosystems, habitat fragmentation has resulted in declines and local extinctions of mammalian and avian terrestrial insectivores. To assess the ability of a tropical rainforest community in Ivory Coast to resist perturbation from such loss of trophic diversity, I traced feedbacks in above and below ground communities and measured changes in nutrient levels and herbivory rates in response to an experimental exclosure of avian and mammalian terrestrial insectivores. I present evidence that loss of this functional group may result in increased tree seedling herbivory and altered nutrient regimes through changes in the abundance and guild structure of invertebrates. Exclusion of top predators of the forest floor resulted in increased seedling herbivory rates and macro‐invertebrat...
Biopedturbation, or animal-caused soil disturbance, may be important for development and maintena... more Biopedturbation, or animal-caused soil disturbance, may be important for development and maintenance of small-scale heterogeneity in ecosystems with the potential to alter seed mortality and recruitment. However, its role in tropical forests has been largely ignored. This study explored effects of vertebrate biopedturbation on seed (1) microsite heterogeneity, (2) predation and (3) germination in a West African rain forest. Exclosure experiments were used to study how biopedturbation altered burial and movements of seeds of four common canopy species. Effect of seed burial on removal by seed predators was also examined. Germination of the dominant canopy species (Raphia palma-pinus) in swamp forest was tested within artificial disturbances mimicking that of a locally common but endangered mammal, the Liberian mongoose (Liberiictis kuhni), which was estimated to turn over the entire forest floor in this habitat in c. 8 mo. Seed exposure to biopedturbation for 20 d (n = 80) led to an overall 6.5-fold increase in small-scale horizontal movement and increased probability of burial (6-52% higher), varying by species. Burial effectively eliminated seed removal for all four species (n = 160) by seed predators over 20 d. Germination of Raphia palma-pinus seeds (n = 100) was enhanced by 17.5% on average over 4 mo in simulated disturbances. Results suggest biopedturbation may be important for seedling recruitment and that loss of species with this functional role could have underappreciated yet important impacts on tropical plant communities.
Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating ... more Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating the strategies and structures by which natural communities of species persist remains a challenge to empirical and theoretical ecologists. We show that simple regulatory feedbacks between autotrophs and their environment when embedded within complex and realistic food-web models enhance biodiversity. The food webs are generated through the niche-model algorithm and coupled with predator-prey dynamics, with and without environmental feedbacks at the autotroph level. With high probability and especially at lower, more realistic connectance levels, regulatory environmental feedbacks result in fewer species extinctions, that is, in increased species persistence. These same feedback couplings, however, also sensitize food webs to environmental stresses leading to abrupt collapses in biodiversity with increased forcing. Feedback interactions between species and their material environments anchor food-web persistence, adding another dimension to biodiversity conservation. We suggest that the regulatory features of two natural systems, deep-sea tubeworms with their microbial consortia and a soil ecosystem manifesting adaptive homeostatic changes, can be embedded within niche-model food-web dynamics.
Understanding the evolution of body size and sexual size dimorphism has been a longstanding goal ... more Understanding the evolution of body size and sexual size dimorphism has been a longstanding goal in evolutionary biology. Previous work has shown that environmental stress can constrain male-biased sexual size dimorphism at the population level, but we know little about how this might translate to geographical patterns of body size and sexual size dimorphism at the species level. Environmental constraints due to a highly seasonal, resource-poor and/or variable environment have often been cited to explain the unusual lack of sexual size dimorphism among Madagascar's diverse and numerous primate taxa; however, empirical tests of this hypothesis are lacking. Using a phylogenetic approach and a geographical information system platform, we explored the role of seasonality, interannual variability and annual measures of temperature and rainfall, and net primary productivity on patterns of body size and sexual size dimorphism across 130 species of primates. Phylogenetically controlled comparisons showed no support for a role of environmental constraints in moderating sexual size dimorphism at the interspecific level, despite significant associations of environmental variables with body mass. Results suggest that the focus of discussions that have dominated in the last two decades regarding the role of environmental constraints in driving patterns of monomorphism of Madagascar's lemurs should be reconsidered; however, the conundrum remains.
Most studies that examine the influence of climatic change on flora and fauna have focused on nor... more Most studies that examine the influence of climatic change on flora and fauna have focused on northern latitudes; however, there is increasing recognition that tropical regions are also being affected. Despite this, regions such as Madagascar, which are rich in endemic biodiversity but may have low adaptive capacity to climatic change, are poorly represented in studies examining the effects of climate variability on biota. We investigated how El Niñ o Southern Oscillations (ENSO) influence precipitation patterns in the rainforest region of southeastern Madagascar (1962-2006) and then constructed models to assess the potential contribution of climatic variables on the reproductive parameters of the Milne Edward's sifaka, a threatened lemur species (Propithecus edwardsi), over a 20-year period. The Southern Oscillation Index of sea surface temperature (SST) anomalies in the tropical Pacific was associated with precipitation patterns including wetter wet seasons during warmer phases and drier dry seasons following cooler phases. The bestsupported models of lemur fecundity (female offspring per female that survive to 1 year of age per year) included cyclone presence during gestation and ENSO phase before conception and during the first 6 months of life. Models also suggested that heavy rains during gestation may limit birth rates and that prolonged drought during female lactation may limit first year offspring survival; although these variables were given little importance for predicting overall fecundity relative to ENSO phases and cyclone presence. Our results linking lemur reproduction with climatic variability suggest that climatic changes may be an additional threat to Madagascar's unique and already endangered flora and fauna. The association between precipitation in southeastern Madagascar and SST anomalies in the tropical Pacific suggests that dynamics of wildlife populations even in tropical areas such as Madagascar can be affected by global climate cycles making them potentially vulnerable to global climate change.
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