Matrix quality and disturbance frequency drive evolution of species behavior at habitat boundaries

Previous theoretical studies suggest that a species' landscape should influence the evolution of its dispersal characteristics, because landscape structure affects the costs and benefits of dispersal. However, these studies have not considered the evolution of boundary crossing, that is, the tendency of animals to cross from habitat to nonhabitat ("matrix"). It is important to understand this dispersal behavior, because of its effects on the probability of population persistence. Boundary-crossing behavior drives the rate of interaction with matrix, and thus, it influences the rate of movement among populations and the risk of dispersal mortality. We used an individual-based, spatially explicit model to simulate the evolution of boundary crossing in response to landscape structure. Our simulations predict higher evolved probabilities of boundary crossing in landscapes with more habitat, less fragmented habitat, higher-quality matrix, and more frequent disturbances (i.e., fewer generations between local population extinction events). Unexpectedly, our simulations also suggest that matrix quality and disturbance frequency have much stronger effects on the evolution of boundary crossing than either habitat amount or habitat fragmentation. Our results suggest that boundary-crossing responses are most affected by the costs of dispersal through matrix and the benefits of escaping local extinction events. Evolution of optimal behavior at habitat boundaries in response to the landscape may have implications for species in human-altered landscapes, because this behavior may become suboptimal if the landscape changes faster than the species' evolutionary response to that change. Understanding how matrix quality and habitat disturbance drive evolution of behavior at boundaries, and how this in turn influences the extinction risk of species in human-altered landscapes should help us identify species of conservation concern and target them for management

Measuring and selecting scales of effect for landscape predictors in species-habitat models

Wildlife managers often use habitat models to determine species habitat requirements and to identify locations for conservation efforts, uses which depend on accurate specification of species-habitat relationships. Prior study suggests that model performance may be influenced by the way we measure environmental predictors. We hypothesized that species responses to landscape predictors are best represented by landscape composition-based measurements, rather than distance-based measurements. We also hypothesized that models using empirical data to select an appropriate scale of effect for each habitat predictor (multiscale models) should perform better than models that assume a common scale of effect for all predictors (single-scale models). To test these hypotheses we constructed habitat models for three mammal species, Mephitis mephitis, Mustela erminea, and Procyon lotor, based on surveys conducted in 80 landscapes in southeastern Ontario, Canada. For each species we compared the performance of distance- and composition-based measurements, and we compared the performance of single- and multi-scale models. The composition-based measurement, measured at its empirically determined scale of effect, had greater explanatory power than the distance-based measurement of a given predictor more often than expected by chance, supporting our first hypothesis. Contrary to expectation, multi-scale models did not have better explanatory power or predictive performance relative to single-scale models. We identified and evaluated four potential mechanisms to explain this, and, depending on the species, we found that the best explanation was either that predictors have significant effects at a common scale or that, although the modeled effects were at multiple scales, they were of similar magnitude and direction at the scales modeled in single- and multi-scale models. Our results suggest that habitat modeling based on distance-based measurements could be improved by including composition-based measurements of landscape predictor variables, but that inclusion of predictor-specific scales of effect for composition-based measurements does not necessarily improve performance over models including composition-based measurements at a single scale. Conservation and wildlife management may be simplified when single-scale models perform as well as multi-scale models, as this suggests actions conducted at a single scale may address management objectives as well as actions taken at different scales for different landscape features

Habitat specialist birds disperse farther and are more migratory than habitat generalist birds

Some theories predict habitat specialists should be less dispersive and migratory than generalists, while other theories predict the opposite. We evaluated the cross-species relationship between the degree of habitat specialization and dispersal and migration status in 101 bird species breeding in North America and the United Kingdom, using empirical estimates of the degree of habitat specialization from breeding bird surveys and mean dispersal distance estimates from large-scale mark-recapture studies. We found that habitat specialists dispersed farther than habitat generalists, and full migrants had more specialized habitat than partial migrants or resident species. To our knowledge this is the first large-scale, multi-species study to demonstrate a positive relationship between the degree of habitat specialization and dispersal, and it is opposite to the pattern found for invertebrates. This finding is particularly interesting because it suggests that trade-offs between the degree of habitat specialization and dispersal ability are not conserved across taxonomic groups. This cautions against extrapolation of trait co-occurrence from one species group to another. In particular, it suggests that efforts aimed at conserving the most habitat-specialist temperate-breeding birds will not lead to conservation of the most dispersal-limited species

Reconciling contradictory relationships between mobility and extinction risk in human-altered landscapes

Some empirical and theoretical studies suggest that more mobile species are less at risk in human-altered landscapes, while others suggest the opposite. We propose three novel hypotheses to explain these contradictory findings: (i) extinction risk increases with increasing mobility when mobility is measured as emigration, but decreases with increasing mobility when mobility is measured as immigration; (ii) the most mobile species (whether measured by emigration or immigration) in unaltered landscapes are least mobile in human-altered landscapes, so the relationship between mobility and risk is opposite when mobility is measured in unaltered and altered landscapes; and (iii) the mobility-risk relationship is ∩-shaped; thus, the relationship is apparently positive when studied species have low-to-intermediate mobility, but negative when species have intermediate-to-high mobility. We also evaluate a fourth hypothesis that had been previously theorized: that some landscape structures drive evolution of dispersal characteristics that increase both mobility and risk, while others drive evolut

Landscape context is more important than wetland buffers for farmland amphibians

In regions with high rates of wetland loss, remnant wetlands and constructed ponds can provide important breeding habitat for amphibians. However, such wetlands are often embedded in a matrix of agricultural fields, potentially putting species within these wetlands at risk. One recommendation for conservation of amphibians in agriculture-dominated landscapes is to maintain a buffer of permanent vegetation around the wetland. However, it is not clear how wide wetland buffers must be to effectively conserve amphibians in agriculture-dominated landscapes or what vegetation types are suitable buffer vegetation. Furthermore, it is not clear whether wetland buffers produce similar—or better—conservation outcomes for amphibians than actions conducted at larger spatial extents. We addressed these questions using data from anuran (frog and toad) breeding call surveys in 36 wetlands in rural eastern Ontario, Canada. First, we tested for the effects of 49 different wetland buffer measurements on anuran richness, relative anuran abundance, and the abundance/probability of occurrence of individual species. These 49 measurements represented all combinations of seven different ways to measure the wetland buffer size and seven types of buffer vegetation. Wetland buffer size was measured as the minimum width of buffer vegetation contiguous with the wetland and proportion of the area within 5, 16, 30, 50, 120, or 300 m of the wetland containing buffer vegetation that was contiguous with the wetland. Then, to compare the strength of effect of wetland buffers versus landscape context on anurans, we compared the wetland buffer measurement with the strongest positive effect on each anuran response (from the previous analysis) to the effects of three landscape-scale variables: area of woodland; area of wetlands, streams, rivers, and lakes; and road density. We did not detect positive effects of wetland buffers on anuran richness or relative anuran abundance. This is because positive effects of wetland buffers on individual species were rare, i.e. positive effects were only supported for two of the six species with enough data to model individually: Amer

The scale of effect of landscape context varies with the species’ response variable measured

Context: To detect an effect of landscape context on a species’ response, the landscape variables need to be measured within the appropriate distance from the species’ response, i.e. at the scale of effect. However, it is not clear what factors determine the scale of effect. Objective: Our objective was to test the prediction that the scale of effect should be smallest when the species’ response is fecundity, larger for abundance, and larger still for occurrence. Methods: We compared the scale of effect of two landscape variables (road density, forest proportion) on the three responses (fecundity, abundance, occurrence) for the wood frog (Lithobates sylvaticus) in eastern Ontario, Canada. We used egg mass surveys of 34 ponds to estimate fecundity (mean eggs/mass), abundance (number of masses), and occurrence (presence/absence of egg masses). We then empirically estimated the scale of effect of each landscape variable on each response. Results: The scale of effect differed among responses, from 0.2 to 3.0 km radii; however, it did not vary in the predicted order. Furthermore, the order was not consistent between the two landscape variables. Conclusions: Our results show that the scale of effect of a landscape variable on a given species can differ for different response variables. However, they also suggest that these differences in the scale of effect are not predictable. Thus, the most reliable way to ensure a landscape context study is conducted at the correct spatial extent is to estimate the scale of effect empirically, rather than ‘guesstimating’ the extent a priori

The spatial scale of time-lagged population synchrony increases with species dispersal distance

Aim: Time-lagged population synchrony, where spatially separated populations show similar fluctuations in abundance lagged over time, is thought to be driven by dispersal among populations. When dispersal is proportional to population density or positively density dependent, and individuals move readily from population A to population B, then as population A increases, the increased number of dispersers from population A to B will cause a subsequent increase in population B. If true, then time-lagged synchrony should be strongest at a species’ typical dispersal distance, because the rate of exchange between populations will be greatest at that distance. Location: United Kingdom (U. K.). Time period: 1994 – 2013. Major taxa studied: Birds (class Aves). Methods: We estimated the spatial scale of 1-year-lagged population synchrony for 76 U.K. bird species, using 20 years of bird count data collected at 2,415 locations by the British Breeding Bird Survey. We then compared these spatial scales with published mean natal and breeding dispersal distance estimates (ranging from 0.1 to 25.8 km) for the same species based on an independent, large-scale, mark–recapture dataset of 492,272 bird recaptures in Britain and Ireland. Results: We found strong, positive cross-species relationships between the spatial scale of time-lagged synchrony and mean natal and breeding dispersal distance estimates from the mark–recapture study. However, average spatial scales of time-lagged synchrony were more than 60 km longer than those from mark–recapture data, with scales ranging from 5 to 185 km. Main conclusions: Ours is the first study to show that the spatial scale of time-lagged synchrony increases with species dispersal distance. The scale of synchrony was larger than expected, probably because mark–recapture data underestimated the real dispersal distances, or because dispersal synchronizes populations at a larger spatial scale than that of dispersal (e.g., through formation of travelling waves), or both. Nevertheless, the strong relative concordance is consistent with the explanation that time-lagged synchrony results from dispersal among populations

Abundance of Aerially-Dispersing Spiders Declines with Increasing Road Traffic

Roads and traffic have been implicated in population declines in a number of taxonomic groups. However, there is little research into the potential effects of roads or traffic on spiders. Here, we tested the prediction that there would be fewer aerially-dispersing (i.e., ballooning) spiders at high-traffic than low-traffic roads. We used custom-made sticky traps attached to a vehicle to collect ballooning spiders along 10 high-traffic-low-traffic rural road pairs in southeastern Ontario, Canada. We collected half as many spiders at high-traffic than low-traffic roads. This provides the first published evidence of negative traffic effects on ballooning spiders. Although consistent with our prediction that ballooning spiders are less abundant at high-traffic roads, there are several possible explanations for this finding. Further study is needed to investigate these explanations, including whether the observed traffic effect reflects reduced population sizes near high-traffic roads or reduced ballooning behaviour near high-traffic roads. If the former, then roads may represent a significant conservation concern for ballooning spider species

Farmland heterogeneity benefits bats in agricultural landscapes

Pressure to increase food production poses a challenge for biodiversity conservation in agricultural landscapes. Previous studies suggest that one potential way to enhance biodiversity without taking land out of production is to increase the landscape heterogeneity of farmland by increasing the diversity of crop types in the landscape, and/or the complexity of the spatial pattern of the crop fields (e.g., by decreasing field sizes). Thus we hypothesize that farmland heterogeneity should also increase bat abundance and richness in agricultural landscapes. Here, we use data on bat activity and richness collected using acoustic surveys in rural eastern Ontario, Canada to test the predictions that there should be greater bat activity and greater species richness in agricultural landscapes with higher Shannon diversity of crops and smaller fields, when controlling for the effect of total crop cover. Bat activity increased with farmland heterogeneity, as predicted. Farmland heterogeneity was also positively related to species richness, although the relationship was not statistically supported. Positive effects of farmland heterogeneity on bats will be of interest to farmers and agricultural policy-makers, given the potential economic benefits of pest control by bats

Flying insect abundance declines with increasing road traffic

One potentially important but underappreciated threat to insects is road mortality. Road kill studies clearly show that insects are killed on roads, leading to the hypothesis that road mortality causes declines in local insect population sizes. In this study we used custom-made sticky traps attached to a vehicle to target diurnal flying insects that interact with roads, sampling along 10 high-traffic and 10 low-traffic rural roads in southeastern Ontario, Canada. We used a paired sampling design to control for potentially confounding differences in the road characteristics (e.g. road width) and surrounding land covers (e.g. housing density) between high-traffic and low-traffic roads. We then used these data to test the prediction that fewer flying insects collide with vehicles, per vehicle (i.e. insect abundance is lower), on high-traffic than low-traffic roads. We found significantly fewer insects at the high-traffic roads than at the low-traffic roads as predicted. There was a 23.5% decline in the number of insects/km/vehicle on high-traffic relative to low-traffic roads. Given the high rates of insect mortality observed in previous studies, it is likely that road mortality contributes to these observed negative effects of traffic intensity. Thus the growing global road network is a concern for conservationists and land managers, not only because insect population declines contribute to the ongoing global losses of biodiversity but also because insects pla