Predation Risk and Vegetation Effects on Avian Diversity, Species Turnover, Reproduction, and Fitness

Vegetation is the habitat that underlies animal distributions. Yet mechanisms by which dynamic changes in vegetation affect animal fitness, distributions, and communities remain unclear. For example, animal richness and species composition often change with decreased forest structural complexity associated with anthropogenic disturbance, but differences in latitude and vegetation effects on reproductive success may influence species responses to vegetation changes. My global meta-analysis of logging effects on bird communities revealed substantial species loss in tropical but not temperate forests. This suggests tropical birds exhibit greater habitat specialization than their temperate relatives. My meta-analysis also suggested that changes in reproductive success can influence how animals distribute themselves in response to vegetation change. I examined this hypothesis with an in-depth observational study and landscape-scale experiment. Habitat use and nest predation rates were examined for 16 bird species that breeding along a deciduous to coniferous vegetation gradient and with experimental conifer removal from aspen stands. For most bird species, decreasing abundance was associated with increasing predation risk along both natural and experimentally modified vegetation gradients. This landscape-scale approach strongly supports the idea that vegetation-mediated effects of predation risk are associated with animal distributions and species turnover. While direct predation mortality clearly has effects on animal population dynamics, the risk of predation alone may have equally large effects on reproduction and, ultimately, fitness. Yet the severity and generality of such demographic ‘costs of fear’ is unknown across species. I tested phenotypic responses to risk and associated demographic costs for 10 songbird species breeding along natural nest predation gradients and by experimentally increasing risk for four species. Parents decreased offspring development periods, reducing time-dependent nest mortality with natural and experimental increases in risk. Reproductive output from nests in the absence of direct predation generally declined along risk gradients, but the severity of this cost varied across species. Ultimately, demographic costs of fear reduced fitness across bird species, but not as strongly as direct predation mortality. These landscape and experimental tests suggest that vegetation affects the perceived risk of predation, and thereby strongly influences avian behaviors, fitness, distributions, and community assembly

The promise and pitfalls of β-diversity in ecology and conservation

A key challenge in ecology and conservation is to determine how processes at different scales create variation in community composition (β-diversity). In this issue, Oldén & Halme show that grazers increase β-diversity through multiple processes at different scales. We discuss how β-diversity can elucidate fundamental processes of community assembly, challenges in linking processes to patterns, and unresolved questions across scales

Integrating species traits into species pools

Despite decades of research on the species‐pool concept and the recent explosion of interest in trait‐based frameworks in ecology and biogeography, surprisingly little is known about how spatial and temporal changes in species‐pool functional diversity (SPFD) influence biodiversity and the processes underlying community assembly. Current trait‐based frameworks focus primarily on community assembly from a static regional species pool, without considering how spatial or temporal variation in SPFD alters the relative importance of deterministic and stochastic assembly processes. Likewise, species‐pool concepts primarily focus on how the number of species in the species pool influences local biodiversity. However, species pools with similar richness can vary substantially in functional‐trait diversity, which can strongly influence community assembly and biodiversity responses to environmental change. Here, we integrate recent advances in community ecology, trait‐based ecology, and biogeography to provide a more comprehensive framework that explicitly considers how variation in SPFD, among regions and within regions through time, influences the relative importance of community assembly processes and patterns of biodiversity. First, we provide a brief overview of the primary ecological and evolutionary processes that create differences in SPFD among regions and within regions through time. We then illustrate how SPFD may influence fundamental processes of local community assembly (dispersal, ecological drift, niche selection). Higher SPFD may increase the relative importance of deterministic community assembly when greater functional diversity in the species pool increases niche selection across environmental gradients. In contrast, lower SPFD may increase the relative importance of stochastic community assembly when high functional redundancy in the species pool increases the influence of dispersal history or ecological drift. Next, we outline experimental and observational approaches for testing the influence of SPFD on assembly processes and biodiversity. Finally, we highlight applications of this framework for restoration and conservation. This species‐pool functional diversity framework has the potential to advance our understanding of how local‐ and regional‐scale processes jointly influence patterns of biodiversity across biogeographic regions, changes in biodiversity within regions over time, and restoration outcomes and conservation efforts in ecosystems altered by environmental change

Impacts of Aspen and Conifer Vegetation on Predation Risk and Distributions of Bird Species

Aspen forests are in decline around the globe and are largely being replaced by conifers.  Associated with this shift in forest composition, we document an increase in nest predation risk and decrease in abundance of bird species that breed in aspens.  These observational data from 5 years across 19 forest stands in western Montana were verified with an adaptive management experiment removing all conifers from three large aspen stands in the Mt. Haggin WMA.  This landscape-scale approach strongly supports the active management of aspen stands, by such methods as removing conifers, to improve breeding bird habitat.  Our results also suggest that vegetation-mediated effects of predation are associated with avian distributions and species turnover

Local Species Diversity, Β-Diversity and Climate Influence the Regional Stability of Bird Biomass Across North America

Biodiversity often stabilizes aggregate ecosystem properties (e.g. biomass) at small spatial scales. However, the importance of species diversity within communities and variation in species composition among communities (β-diversity) for stability at larger scales remains unclear. Using a continental-scale analysis of 1657 North American breeding-bird communities spanning 20-years and 35 ecoregions, we show local species diversity and β-diversity influence two components of regional stability: local stability (stability of bird biomass within sites) and spatial asynchrony (asynchronous fluctuations in biomass among sites). We found spatial asynchrony explained three times more variation in regional stability of bird biomass than did local stability. This result contrasts with studies at smaller spatial scales—typically plant metacommunities under 1 ha—that find local stability to be more important than spatial asynchrony. Moreover, spatial asynchrony of bird biomass increased with bird β-diversity and climate heterogeneity (temperature and precipitation), while local stability increased with species diversity. Our study reveals new insights into the scale-dependent processes regulating ecosystem stability, providing evidence that both local biodiversity loss and homogenization can destabilize ecosystem processes at biogeographic scales

Negative density dependence mediates biodiversity–productivity relationships across scales

Regional species diversity generally increases with primary productivity whereas local diversity–productivity relationships are highly variable. This scale-dependence of the biodiversity–productivity relationship highlights the importance of understanding the mechanisms that govern variation in species composition among local communities, which is known as β-diversity. Hypotheses to explain changes in β-diversity with productivity invoke multiple mechanisms operating at local and regional scales, but the relative importance of these mechanisms is unknown. Here we show that changes in the strength of local density-dependent interactions within and among tree species explain changes in β-diversity across a subcontinental-productivity gradient. Stronger conspecific relative to heterospecific negative density dependence in more productive regions was associated with higher local diversity, weaker habitat partitioning (less species sorting), and homogenization of community composition among sites (lower β-diversity). Regional processes associated with changes in species pools had limited effects on β-diversity. Our study suggests that systematic shifts in the strength of local interactions within and among species might generally contribute to some of the most prominent but poorly understood gradients in global biodiversity

Tree Species Diversity Increases with Conspecific Negative Density Dependence Across an Elevation Gradient

Elevational and latitudinal gradients in species diversity may be mediated by biotic interactions that cause density-dependent effects of conspecifics on survival or growth to differ from effects of heterospecifics (i.e. conspecific density dependence), but limited evidence exists to support this. We tested the hypothesis that conspecific density dependence varies with elevation using over 40 years of data on tree survival and growth from 23 old-growth temperate forest stands across a 1,000-m elevation gradient. We found that conspecific-density-dependent effects on survival of small-to-intermediate-sized focal trees were negative in lower elevation, higher diversity forest stands typically characterised by warmer temperatures and greater relative humidity. Conspecific-density-dependent effects on survival were less negative in higher elevation stands and ridges than in lower elevation stands and valley bottoms for small-to-intermediate-sized trees, but were neutral for larger trees across elevations. Conspecific-density-dependent effects on growth were negative across all tree size classes and elevations. These findings reveal fundamental differences in biotic interactions that may contribute to relationships between species diversity, elevation and climate

Epicardial adipose tissue measured by magnetic resonance imaging predicts abnormal adenosine stress cardiovascular magnetic resonance imaging and future adverse cardiovascular events

Background A growing body of evidence demonstrates a quantitative association between Epicardial Adipose Tissue (EAT), cardiometabolic risk factors and measures of coronary artery disease (CAD). It is still unclear, however, if EAT is predictive of abnormal functional stress tests and clinical outcomes. The aim of this study is to elucidate the relationship between the total volume of EAT, the detection of ischemia and/or infarct with Adenosine Stress Cardiovascular Magnetic Resonance imaging (AS-CMR), and combined future adverse cardiovascular events. Method

Bird species turnover is related to changing predation risk along a vegetation gradient

Abstract. Turnover in animal species along vegetation gradients is often assumed to reflect adaptive habitat preferences that are narrower than the full gradient. Specifically, animals may decline in abundance where their reproductive success is low, and these poorquality locations differ among species. Yet habitat use does not always appear adaptive. The crucial tests of how abundances and demographic costs of animals vary along experimentally manipulated vegetation gradients are lacking. We examined habitat use and nest predation rates for 16 bird species that exhibited turnover with shifts in deciduous and coniferous vegetation. For most bird species, decreasing abundance was associated with increasing predation rates along both natural and experimentally modified vegetation gradients. This landscape-scale approach strongly supports the idea that vegetation-mediated effects of predation are associated with animal distributions and species turnover