Which plant traits predict species loss in calcareous grasslands with extinction debt?

Aim Habitat loss and degradation pose a major threat to biodiversity, which can result in the extinction of habitat characteristic species. However, many species exhibit a delayed response to environmental changes because of the slow intrinsic dynamics of populations, resulting in extinction debt. We assess directly the changes in habitat characteristic species composition by comparing historical (1923) and current inventories in highly fragmented grasslands. We aim to characterize the species that constitute extinction debt in European calcareous grasslands. Location Europe, Estonia, 59–60° N, 24–25° E. Methods We related eleven life‐history traits and selected habitat preferences to local extinctions of populations in grasslands where extinction debt has been largely paid. Traits were chosen to describe species dispersal and persistence abilities and were quantified from databases. Results The studied grasslands have lost 90% of their area and 30% of their characteristic plant populations in 90 years. Species more prone to local population extinction were characterized by shorter life span, self‐pollination, a lack of clonal growth, fewer seeds per shoot, lower average height, lower soil nitrogen preference and higher requirements for light, indicating a limited ability to tolerate the range of changes in biotic and abiotic conditions of the sites. Locally extinct populations were also characterized by wind‐dispersed seeds, lower seed weight and lower terminal velocity of seeds, suggesting that species strategies for long‐distance dispersal are not favoured in highly fragmented landscapes. Thus, both increased habitat isolation and decreased habitat quality are important in determining local population extinction. Main conclusions Populations more prone to local extinction were characterized by a number of life‐history traits, demonstrating a greater extinction risk for species with poorer abilities for local persistence and competition. Our results can be applied to less degraded grasslands where the extinction debt is not yet paid to determine those species most susceptible to future extinction.     

Homogenization of dispersal ability across bird species in response to landscape change

Human land use is known to homogenize biotic communities, increasing similarity in their genetic, taxonomic and functional diversity. Explanations have focused almost exclusively on human‐mediated extinction and range expansion. However, homogenization could also be produced by land use driving selection for similar traits across species. We propose a novel hypothesis to explain how human land use homogenizes dispersal ability across species. With habitat loss and increasing human land use intensities there should be larger increases in the costs of dispersal for dispersive than sedentary species, because dispersive species interact with non‐habitat more frequently. In contrast, the benefits of dispersal should increase more for sedentary than dispersive species, because sedentary species are at greater risk from inbreeding depression, predation and competition associated with habitat loss. Therefore we predict that sedentary species become more dispersive in a human‐altered landscape, and dispersive species more sedentary. We tested this prediction using wing pointedness to estimate the initial dispersal ability and change in dispersal ability for 21 North American passerines over the 20th century. More pointed wings are associated with stronger dispersal ability. Thus our prediction would be supported by a negative cross‐species relationship between these two measurements. We found a strong, negative relationship, as predicted. This resulted in declines in the variability in wing pointedness among species over time. Although other things can cause wing shape to change, including changes in habitat availability, none of these explained the observed relationship. Our result provides the first evidence that human landscape alteration is homogenizing bird communities, driving selection for intermediate dispersal ability across species. It also implies that more dispersive species are more at‐risk from human landscape use because, when rates of landscape alteration are faster than a species’ ability to adapt to that change, the costs of dispersal increase more for dispersive than sedentary species.     

Relative importance of landscape and species characteristics on extinction debt,immigration credit and relaxation time after habitat turnover

Habitat turnover concomitantly causes destruction and creation of habitat patches. Following such a perturbation, metapopulations harbor either an extinction debt or an immigration credit, that is the future decrease or increase in population numbers due to this disturbance. Extinction debt and immigration credit are rarely considered simultaneously and disentangled from the relaxation time (time to new equilibrium). In this contribution, we test the relative importance of two potential drivers of time-delayed metapopulation dynamics: the spatial configuration of the habitat turnover and species dispersal ability. We provide a simulation-based investigation projecting metapopulation dynamics following habitat turnover in virtual landscapes. We consider two virtual species (a short-distance and a long-distance disperser) and five scenarios of habitat turnover depending on net habitat loss or gain and habitat aggregation. Our analyses reveal that (a) the main determinant of the magnitude of the extinction debt or immigration credit is the net change in total habitat area, followed by species dispersal distance and finally by the post-turnover habitat aggregation; (b) relaxation time weakly depends on the magnitude of the immigration credit or of the extinction debt; (c) the main determinant of relaxation time is dispersal distance followed by the net change in total habitat area and finally by the post-turnover habitat aggregation. These results shed light on the relative importance of dispersal ability and habitat turnover spatial structure on the components of time-delayed metapopulation dynamics.     

Traits related to species persistence and dispersal explain changes in plant communities subjected to habitat loss

Aim Habitat fragmentation is a major driver of biodiversity loss but it is insufficiently known how much its effects vary among species with different life‐history traits; especially in plant communities, the understanding of the role of traits related to species persistence and dispersal in determining dynamics of species communities in fragmented landscapes is still limited. The primary aim of this study was to test how plant traits related to persistence and dispersal and their interactions modify plant species vulnerability to decreasing habitat area and increasing isolation. Location Five regions distributed over four countries in Central and Northern Europe. Methods Our dataset was composed of primary data from studies on the distribution of plant communities in 300 grassland fragments in five regions. The regional datasets were consolidated by standardizing nomenclature and species life‐history traits and by recalculating standardized landscape measures from the original geographical data. We assessed the responses of plant species richness to habitat area, connectivity, plant life‐history traits and their interactions using linear mixed models. Results We found that the negative effect of habitat loss on plant species richness was pervasive across different regions, whereas the effect of habitat isolation on species richness was not evident. This area effect was, however, not equal for all the species, and life‐history traits related to both species persistence and dispersal modified plant sensitivity to habitat loss, indicating that both landscape and local processes determined large‐scale dynamics of plant communities. High competitive ability for light, annual life cycle and animal dispersal emerged as traits enabling species to cope with habitat loss. Main conclusions In highly fragmented rural landscapes in NW Europe, mitigating the spatial isolation of remaining grasslands should be accompanied by restoration measures aimed at improving habitat quality for low competitors, abiotically dispersed and perennial, clonal species.     

A process‐based model supports an association between dispersal and the prevalence of species traits in tropical reef fish assemblages

Habitat dynamics interacting with species dispersal abilities could generate gradients in species diversity and prevalence of species traits when the latter are associated with species dispersal potential. Using a process‐based model of diversification constrained by a dispersal parameter, we simulated the interplay between reef habitat dynamics during the past 140 million years and dispersal, shaping lineage diversification history and assemblage composition globally. The emerging patterns from the simulations were compared to current prevalence of species traits related to dispersal for 6315 tropical reef fish species. We found a significant spatial congruence between the prevalence of simulated low dispersal values and areas with a large proportion of species characterized by small adult body size, narrow home range mobility behaviour, pelagic larval duration shorter than 21 days and diurnal activity. Species characterized by such traits were found predominantly in the Indo‐Australian Archipelago and the Caribbean Sea. Furthermore, the frequency distribution of the dispersal parameter was found to match empirical distributions for body size, PLD and home range mobility behaviour. Also, the dispersal parameter in the simulations was associated to diversification rates and resulted in trait frequency matching empirical distributions. Overall, our findings suggest that past habitat dynamics, in conjunction with dispersal processes, influenced diversification in tropical reef fishes, which may explain the present‐day geography of species traits.     

Fragmentation of Atlantic Forest has not affected gene flow of a widespread seed‐dispersing bat

Habitat loss and resultant fragmentation are major threats to biodiversity, particularly in tropical and subtropical ecosystems. It is increasingly urgent to understand fragmentation effects, which are often complex and vary across taxa, time and space. We determined whether recent fragmentation of Atlantic forest is causing population subdivision in a widespread and important Neotropical seed disperser: Artibeus lituratus (Chiroptera: Phyllostomidae). Genetic structure within highly fragmented forest in Paraguay was compared to that in mostly contiguous forest in neighbouring Misiones, Argentina. Further, observed genetic structure across the fragmented landscape was compared with expected levels of structure for similar time spans in realistic simulated landscapes under different degrees of reduction in gene flow. If fragmentation significantly reduced successful dispersal, greater population differentiation and stronger isolation by distance would be expected in the fragmented than in the continuous landscape, and genetic structure in the fragmented landscape should be similar to structure for simulated landscapes where dispersal had been substantially reduced. Instead, little genetic differentiation was observed, and no significant correlation was found between genetic and geographic distance in fragmented or continuous landscapes. Furthermore, comparison of empirical and simulated landscapes indicated empirical results were consistent with regular long‐distance dispersal and high migration rates. Our results suggest maintenance of high gene flow for this relatively mobile and generalist species, which could be preventing or significantly delaying reduction in population connectivity in fragmented habitat. Our conclusions apply to A. lituratus in Interior Atlantic Forest, and do not contradict broad evidence that habitat fragmentation is contributing to extinction of populations and species, and poses a threat to biodiversity worldwide.     

Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population

1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations. 2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration. 3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes. 4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners. 5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes.     

Local native plant diversity responds to habitat loss and fragmentation over different time spans and spatial scales

Separating the threats that habitat loss and habitat fragmentation pose to biodiversity is challenging because these processes usually occur simultaneously. Additionally, their importance may be underestimated due to time-delayed extinction. In central Texas savannas, woody plant encroachment reduces the amount of habitat available to herbaceous species while fragmenting remaining habitat. We examined the relationships between present species richness and present and past habitat amount and fragmentation (measured as fractal dimension) using a series of aerial photographs taken over nearly 60 years. We show that woody plant encroachment, a common phenomenon in savannas worldwide, reduces the diversity of herbaceous vegetation through both habitat loss and fragmentation. Habitat loss has the strongest impact on species richness over short time spans and small spatial scales in these savannas. Habitat fragmentation, however, has the strongest impact over longer time spans and larger spatial scales and generates long-term extinction debts. We also demonstrate that examining habitat loss and habitat fragmentation across different time periods and at different spatial scales is essential for understanding their joint and individual effects on plant community composition.     

Fitness declines towards range limits and local adaptation to climate affect dispersal evolution during climate‐induced range shifts

Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low‐latitude/low‐elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: (i) climate‐induced fitness declines towards range limits and (ii) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual‐based model. We compare range‐wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines towards range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. During climate stability, dispersal decreased towards RLs when fitness was uniform, but increased when fitness declined towards RLs, due to highly dispersive genotypes maintaining sink populations at RLs, increased kin selection in smaller populations, and an emergent fitness asymmetry that favoured dispersal in low‐quality habitat. However, this initial dispersal advantage at low‐fitness RLs did not facilitate climate tracking, as it was outweighed by an increased probability of extinction. Locally adapted genotypes benefited from staying close to their climate optima; this selected against dispersal under stable climates but for increased dispersal throughout shifting ranges, compared to cases without local adaptation. Dispersal increased at expanding RLs in most scenarios, but only increased at the range centre and contracting RLs given local adaptation to climate.     

Habitat loss-induced tipping points in metapopulations with facilitation

Habitat loss is known to pervade extinction thresholds in metapopulations. Such thresholds result from a loss of stability that can eventually lead to collapse. Several models have been developed to understand the nature of these transitions and how they are affected by the locality of interactions, fluctuations or external drivers. Most models consider the impact of grazing or aridity as a control parameter that can trigger sudden shifts, once critical values are reached. Others explore instead the role played by habitat loss and fragmentation. Here we consider a minimal model incorporating facilitation between the individuals of the same species along with habitat destruction, with the aim of understanding how local cooperation and habitat loss interact with each other. A mathematical model incorporating facilitation and habitat destruction is derived, along with a spatially explicit simulation model. It is found that a catastrophic shift is expected for increasing levels of habitat loss, but the bifurcation becomes continuous when dispersal is local. Under these conditions, spatial patchiness is found and the qualitative change from discontinuous to continuous results are in agreement with previous studies on ecological systems. Our results suggest that species exhibiting facilitation and displaying short-range dispersal will be markedly more capable of avoiding catastrophic tipping points.     

Closing the gaps for animal seed dispersal: Separating the effects of habitat loss on dispersal distances and seed aggregation

Habitat loss can alter animal movements and disrupt animal seed dispersal mutualisms; however, its effects on spatial patterns of seed dispersal are not well understood. To explore the effects of habitat loss on seed dispersal distances and seed dispersion (aggregation), we created a spatially explicit, individual‐based model of an animal dispersing seeds (SEADS—Spatially Explicit Animal Dispersal of Seeds) in a theoretical landscape of 0%–90% habitat loss based on three animal traits: movement distance, gut retention time, and time between movements. Our model design had three objectives: to determine the effects of (1) animal traits and (2) habitat loss on seed dispersal distances and dispersion and (3) determine how animal traits could mitigate the negative effects of habitat loss on these variables. SEADS results revealed a complex interaction involving all animal traits and habitat loss on dispersal distances and dispersion, driven by a novel underlying mechanism of fragment entrapment. Unexpectedly, intermediate habitat loss could increase dispersal distances and dispersion relative to low and high habitat loss for some combinations of animal traits. At intermediate habitat loss, movement between patches was common, and increased dispersal distances and dispersion compared to continuous habitats because animals did not stop in spaces between fragments. However, movement between patches was reduced at higher habitat loss as animals became trapped in fragments, often near the parent plant, and dispersed seeds in aggregated patterns. As movement distance increased, low time between movements and high gut retention time combinations permitted more movement to adjacent patches than other combinations of animal traits. Because habitat loss affects movement in a nonlinear fashion under some conditions, future empirical tests would benefit from comparisons across landscapes with more than two levels of fragmentation.     

Life history of the Glanville fritillary butterfly in fragmented versus continuous landscapes

Habitat loss and fragmentation threaten the long‐term viability of innumerable species of plants and animals. At the same time, habitat fragmentation may impose strong natural selection and lead to evolution of life histories with possible consequences for demographic dynamics. The Baltic populations of the Glanville fritillary butterfly (Melitaea cinxia) inhabit regions with highly fragmented habitat (networks of small dry meadows) as well as regions with extensive continuous habitat (calcareous alvar grasslands). Here, we report the results of common garden studies on butterflies originating from two highly fragmented landscapes (FL) in Finland and Sweden and from two continuous landscapes (CL) in Sweden and Estonia, conducted in a large outdoor cage (32 by 26 m) and in the laboratory. We investigated a comprehensive set of 51 life‐history traits, including measures of larval growth and development, flight performance, and adult reproductive behavior. Seventeen of the 51 traits showed a significant difference between fragmented versus CL. Most notably, the growth rate of postdiapause larvae and several measures of flight capacity, including flight metabolic rate, were higher in butterflies from fragmented than CL. Females from CL had shorter intervals between consecutive egg clutches and somewhat higher life‐time egg production, but shorter longevity, than females from FL. These results are likely to reflect the constant opportunities for oviposition in females living in continuous habitats, while the more dispersive females from FL allocate more resources to dispersal capacity at the cost of egg maturation rate. This study supports theoretical predictions about small population sizes and high rate of population turnover in fragmented habitats selecting for increased rate of dispersal, but the results also indicate that many other life‐history traits apart from dispersal are affected by the degree of habitat fragmentation.     

Demographic consequences of population subdivision on the long-furred woolly mouse opossum (Micoureus paraguayanus) from the Atlantic Forest

Habitat destruction and fragmentation severely affected the Atlantic Forest. Formerly contiguous populations may become subdivided into a larger number of smaller populations, threatening their long-term persistence. The computer package VORTEX was used to simulate the consequences of habitat fragmentation and population subdivision on Micoureus paraguayanus, an endemic arboreal marsupial of the Atlantic Forest. Scenarios simulated hypothetical populations of 100 and 2000 animals being partitioned into 1–10 populations, linked by varying rates of inter-patch dispersal, and also evaluated male-biased dispersal. Results demonstrated that a single population was more stable than an ensemble of populations of equal size, irrespective of dispersal rate. Small populations (10–20 individuals) exhibited high instability due to demographic stochasticity, and were characterized by high rates of extinction, smaller values for metapopulation growth and larger fluctuations in population size and growth rate. Dispersal effects on metapopulation persistence were related to the size of the populations and to the sexes that were capable of dispersing. Male-biased dispersal had no noticeable effects on metapopulation extinction dynamics, whereas scenarios modelling dispersal by both sexes positively affected metapopulation dynamics through higher growth rates, smaller fluctuations in growth rate, larger final metapopulation sizes and lower probabilities of extinction. The present study highlights the complex relationships between metapopulation size, population subdivision, habitat fragmentation, rate of inter-patch dispersal and sex-biased dispersal and indicates the importance of gaining a better understanding of dispersal and its interactions with correlations between disturbance events.     

Confounding factors in the detection of species responses to habitat fragmentation

Habitat loss has pervasive and disruptive impacts on biodiversity in habitat remnants. The magnitude of the ecological impacts of habitat loss can be exacerbated by the spatial arrangement -- or fragmentation -- of remaining habitat. Fragmentation per se is a landscape-level phenomenon in which species that survive in habitat remnants are confronted with a modified environment of reduced area, increased isolation and novel ecological boundaries. The implications of this for individual organisms are many and varied, because species with differing life history strategies are differentially affected by habitat fragmentation. Here, we review the extensive literature on species responses to habitat fragmentation, and detail the numerous ways in which confounding factors have either masked the detection, or prevented the manifestation, of predicted fragmentation effects.Large numbers of empirical studies continue to document changes in species richness with decreasing habitat area, with positive, negative and no relationships regularly reported. The debate surrounding such widely contrasting results is beginning to be resolved by findings that the expected positive species-area relationship can be masked by matrix-derived spatial subsidies of resources to fragment-dwelling species and by the invasion of matrix-dwelling species into habitat edges. Significant advances have been made recently in our understanding of how species interactions are altered at habitat edges as a result of these changes. Interestingly, changes in biotic and abiotic parameters at edges also make ecological processes more variable than in habitat interiors. Individuals are more likely to encounter habitat edges in fragments with convoluted shapes, leading to increased turnover and variability in population size than in fragments that are compact in shape. Habitat isolation in both space and time disrupts species distribution patterns, with consequent effects on metapopulation dynamics and the genetic structure of fragment-dwelling populations. Again, the matrix habitat is a strong determinant of fragmentation effects within remnants because of its role in regulating dispersal and dispersal-related mortality, the provision of spatial subsidies and the potential mediation of edge-related microclimatic gradients.We show that confounding factors can mask many fragmentation effects. For instance, there are multiple ways in which species traits like trophic level, dispersal ability and degree of habitat specialisation influence species-level responses. The temporal scale of investigation may have a strong influence on the results of a study, with short-term crowding effects eventually giving way to long-term extinction debts. Moreover, many fragmentation effects like changes in genetic, morphological or behavioural traits of species require time to appear. By contrast, synergistic interactions of fragmentation with climate change, human-altered disturbance regimes, species interactions and other drivers of population decline may magnify the impacts of fragmentation. To conclude, we emphasise that anthropogenic fragmentation is a recent phenomenon in evolutionary time and suggest that the final, long-term impacts of habitat fragmentation may not yet have shown themselves.     

Changes in occurrence,richness, and biological traits of dragonflies and damselflies (Odonata) in California and Nevada over the past century

Increases in water demand, urbanization, and severity of drought threaten freshwater ecosystems of the arid western United States. Historical assessments of change in assemblages over time can help determine the effects of these stressors but, to date, are rare. In the present study, we resurveyed 45 sites originally sampled in 1914–1915 for Odonata (dragonflies and damselflies) adults throughout central California and northwestern Nevada, USA. We examined changes in species occurrence rates, taxonomic richness, and biological trait composition in relation to climate changes and human population increases. While species richness at individual sites did not change significantly, we found that odonate assemblages have become more similar across sites. Homogenization is a result of the expansion of highly mobile habitat generalists, and the decline of both habitat specialists and species with an overwintering diapause stage. Using a multi-species mixed-effects model, we found that overall occurrences of Odonata increased with higher minimum temperatures. Habitat specialists and species with a diapause stage, however, occurred less often in warmer regions and more often in areas with higher precipitation. Habitat specialists occurred less often in highly populated sites. Life history traits of Odonata, such as dispersal ability, habitat specialization, and diapause, are useful predictors of species-specific responses to urbanization and climate change in this region.     

Climate change and habitat destruction: a deadly anthropogenic cocktail

Climate change and habitat destruction are two of the greatest threats to global biodiversity. Lattice models have been used to investigate how hypothetical species with different characteristics respond to habitat loss. The main result shows that a sharp threshold in habitat availability exists below which a species rapidly becomes extinct. Here, a similar modelling approach is taken to establish what determines how species respond to climate change. A similar threshold exists for the rate of climate change as has been observed for habitat loss-patch occupancy remains high up to a critical rate of climate change, beyond which species extinction becomes likely. Habitat specialists, especially those of relatively poor colonizing ability are least able to keep pace with climate change. The interaction between climate change and habitat loss might be disastrous. During climate change, the habitat threshold occurs sooner. Similarly, species suffer more from climate change in a fragmented habitat.     

Using basic plant traits to predict ungulate seed dispersal potential

Habitat fragmentation contributes to the decline of plant species by decreasing gene flow among populations. Restoring connectivity among habitat patches is therefore a major issue for plant conservation. However, deciding where to focus restoration efforts requires identifying suitable dispersers for each target plant species. We collected data from the literature on wild and domesticated ungulates, known to be effective seed dispersers, and on the plants they dispersed in Europe via epi‐ and/or endozoochory. We performed a systematic literature review to identify plant and animal traits relevant for seed dispersal. We first modeled the relationships between epi‐ or endozoochory and a priori selected plant traits (diaspore releasing height, length, shape and morphology, and habitat openness). The differences we underlined between the two dispersal mechanisms justified splitting our analyses accordingly. Then, for each dispersal mechanism, we asked whether basic plant traits could be used to predict specific traits of ungulates as endozoochorous or epizoochorous seed dispersers. We modeled the relationships between a priori selected ungulate traits for epizoochory (habitat openness, shoulder height, hair curliness, and hair length) and for endozoochory (habitat openness, body mass, feeding type and digestive system) and plant traits. Plant habitat openness and diaspore morphology were the predictors that most often explained differences among ungulates for epizoochory, whereas plant habitat openness and diaspore releasing height most often explained differences for endozoochory. Our trait‐based predictive models can help improve our ability to propose more precise management decisions for the conservation of plant populations worldwide by taking into account ungulate dispersers.     

Habitat choice stabilizes metapopulation dynamics by enabling ecological specialization

Dispersal is a key trait responsible for the spread of individuals and genes among local populations, thereby generating eco‐evolutionary interactions. Especially in heterogeneous metapopulations, a tight coupling between dispersal, population dynamics and the evolution of local adaptation is expected. In this respect, dispersal should counteract ecological specialization by redistributing locally selected phenotypes (i.e. migration load). Habitat choice following an informed dispersal decision, however, can facilitate the evolution of ecological specialization. How such informed decisions influence metapopulation size and variability is yet to be determined. By means of individual‐based modelling, we demonstrate that informed decisions about both departure and settlement decouple the evolution of dispersal and that of generalism, selecting for highly dispersive specialists. Choice at settlement is based on information from the entire dispersal range, and therefore decouples dispersal from ecological specialization more effectively than choice at departure, which is only based on local information. Additionally, habitat choice at departure and settlement reduces local and metapopulation variability because of the maintenance of ecological specialization at all levels of dispersal propensity. Our study illustrates the important role of habitat choice for dynamics of spatially structured populations and thus emphasizes the importance of considering that dispersal is often informed.     

Adaptive dispersal strategies and the dynamics of a range expansion

In species undergoing range expansion, newly established populations are often more dispersive than older populations. Because dispersal phenotypes are complex and often costly, it is unclear how highly dispersive phenotypes are maintained in a species to enable their rapid expression during periods of range expansion. Here I test the idea that metapopulation dynamics of local extinction and recolonization maintain distinct dispersal strategies outside the context of range expansion. Western bluebirds display distinct dispersal phenotypes where aggressive males are more dispersive than nonaggressive males, resulting in highly aggressive populations at the edge of their expanding range. I experimentally created new habitat interior to the range edge to show that, as on the range front, it was colonized solely by aggressive males. Moreover, fitness consequences of aggression depended on population age: aggressive males had high fitness when colonizing new populations, while nonaggressive males performed best in an older population. These results suggest that distinct dispersal strategies were maintained before range expansion as an adaptation for the continual recolonization of new habitat. These results emphasize similarities between range expansion and metapopulation dynamics and suggest that preexisting adaptive dispersal strategies may explain rapid changes in dispersal phenotypes during range expansion.     

Threat Diversity Will Erode Mammalian Phylogenetic Diversity in the Near Future

To reduce the accelerating rate of phylogenetic diversity loss, many studies have searched for mechanisms that could explain why certain species are at risk, whereas others are not. In particular, it has been demonstrated that species might be affected by both extrinsic threat factors as well as intrinsic biological traits that could render a species more sensitive to extinction; here, we focus on extrinsic factors. Recently, the International Union for Conservation of Nature developed a new classification of threat types, including climate change, urbanization, pollution, agriculture and aquaculture, and harvesting/hunting. We have used this new classification to analyze two main factors that could explain the expected future loss of mammalian phylogenetic diversity: 1. differences in the type of threats that affect mammals and 2. differences in the number of major threats that accumulate for a single species. Our results showed that Cetartiodactyla, Diprotodontia, Monotremata, Perissodactyla, Primates, and Proboscidea could lose a high proportion of their current phylogenetic diversity in the coming decades. In contrast, Chiroptera, Didelphimorphia, and Rodentia could lose less phylogenetic diversity than expected if extinctions were random. Some mammalian clades, including Marsupiala, Chiroptera, and a subclade of Primates, are affected by particular threat types, most likely due solely to their geographic locations and associations with particular habitats. However, regardless of the geography, habitat, and taxon considered, it is not the threat type, but the threat diversity that determines the extinction risk for species and clades. Thus, some mammals might be randomly located in areas subjected to a large diversity of threats; they might also accumulate detrimental traits that render them sensitive to different threats, which is a characteristic that could be associated with large body size. Any action reducing threat diversity is expected to have a significant impact on future mammalian phylogeny.