Thermal and energetic constraints on ectotherm abundance: a global test using lizards

Population densities of birds and mammals have been shown to decrease with body mass at approximately the same rate as metabolic rates increase, indicating that energetic needs constrain endotherm population densities. In ectotherms, the exponential increase of metabolic rate with body temperature suggests that environmental temperature may additionally constrain population densities. Here we test simple bioenergetic models for an ecologically important group of ectothermic vertebrates by examining 483 lizard populations. We find that lizard population densities decrease as a power law of body mass with a slope approximately inverse to the slope of the relationship between metabolic rates and body mass. Energy availability should limit population densities. As predicted, environmental productivity has a positive effect on lizard density, strengthening the relationship between lizard density and body mass. In contrast, the effect of environmental temperature is at most weak due to behavioral thermoregulation, thermal evolution, or the temperature dependence of ectotherm performance. Our results provide initial insights into how energy needs and availability differentially constrain ectotherm and endotherm density across broad spatial scales.     

Grassland songbird survival and recruitment in agricultural landscapes: implications for source-sink demography

Population growth and decline are particularly sensitive to changes in three key life-history parameters: annual productivity, juvenile survival, and adult survival. However, for many species these parameters remain unknown. For example, although grassland songbirds are imperiled throughout North America, for this guild, only a small number of studies have assessed these parameters. From 2002 to 2006, in the agricultural landscape of the Champlain Valley of Vermont and New York, USA, we studied Savannah Sparrow (Passerculus sandwichensis) and Bobolink (Dolichonyx oryzivorus) demography on four grassland treatments: (1) early-hayed fields cut before 11 June and again in early- to mid-July; (2) middle-hayed fields cut once between 21 June and 10 July; (3) late-hayed fields cut after 1 August; and (4) rotationally grazed pastures. We assessed whether these treatments affected adult apparent survival (phi) and recruitment (f), how sensitive these parameters were to the presence of nonbreeders and local dispersal, and the populations' ability to persist in these four habitats. On average, birds using late-hayed fields had > 25% higher apparent survival than those on the more intensively managed early-hayed, middle-hayed, and grazed fields. Overall male phi was 35% higher than female phi, and Savannah Sparrow phi was 44% higher than Bobolink phi. Across all analyses and treatments, apparent survival estimates were 0.58-0.85 for male and 0.48-0.71 for female Savannah Sparrows, and 0.52-0.70 for male and 0.19-0.55 for female Bobolinks. For males of both species, potential nonbreeders decreased the precision of and lowered apparent survival estimates by 25%; female estimates showed little variation with the inclusion of nonbreeders. Inclusion of local dispersal observations increased apparent survival estimates and, in many cases, increased precision, though the effect was stronger for Savannah Sparrows than for Bobolinks, and also stronger for males than for females. High Savannah Sparrow apparent survival rates resulted in stable or near stable populations (lambda approximately 1), particularly in late-hayed and grazed fields, while low Bobolink apparent survival rates resulted in strongly declining populations (lambda < 1) in all treatments.     

Understanding and managing the interactions of impacts from nature-based recreation and climate change

Disturbance to ecosystems in parks and protected areas from nature-based tourism and recreation is increasing in scale and severity, as are the impacts of climate change—but there is limited research examining the degree to which these anthropogenic disturbances interact. In this perspective paper, we draw on the available literature to expose complex recreation and climate interactions that may alter ecosystems of high conservation value such that important species and processes no longer persist. Our emphasis is on ecosystems in high demand for tourism and recreation that also are increasingly experiencing stress from climate change. We discuss the importance of developing predictive models of direct and indirect effects, including threshold and legacy effects at different levels of biological organization. We present a conceptual model of these interactions to initiate a dialog among researchers and managers so that new research approaches and managerial frameworks are advanced to address this emerging issue.     

Does including physiology improve species distribution model predictions of responses to recent climate change?

Thermal constraints on development are often invoked to predict insect distributions. These constraints tend to be characterized in species distribution models (SDMs) by calculating development time based on a constant lower development temperature (LDT). Here, we assessed whether species-specific estimates of LDT based on laboratory experiments can improve the ability of SDMs to predict the distribution shifts of six U.K. butterflies in response to recent climate warming. We find that species-specific and constant (5 degrees C) LDT degree-day models perform similarly at predicting distributions during the period of 1970-1982. However, when the models for the 1970-1982 period are projected to predict distributions in 1995-1999 and 2000-2004, species-specific LDT degree-day models modestly outperform constant LDT degree-day models. Our results suggest that, while including species-specific physiology in correlative models may enhance predictions of species' distribution responses to climate change, more detailed models may be needed to adequately account for interspecific physiological differences.     

Species' traits predict phenological responses to climate change in butterflies

How do species' traits help identify which species will respond most strongly to future climate change? We examine the relationship between species' traits and phenology in a well-established model system for climate change, the U.K. Butterfly Monitoring Scheme (UKBMS). Most resident U.K. butterfly species have significantly advanced their dates of first appearance during the past 30 years. We show that species with narrower larval diet breadth and more advanced overwintering stages have experienced relatively greater advances in their date of first appearance. In addition, species with smaller range sizes have experienced greater phenological advancement. Our results demonstrate that species' traits can be important predictors of responses to climate change, and they suggest that further investigation of the mechanisms by which these traits influence phenology may aid in understanding species' responses to current and future climate change.     

Sustainable livelihoods and people’s vulnerability in the face of coastal hazards

The present study investigates into the link between people’s vulnerability in the face of coastal hazards and sustainable livelihoods. It focuses on the town of Borongan in the Philippines and draws on questionnaire-based surveys and focus group discussions. This research shows that local fishermen are often compelled to go out fishing despite pending typhoon or storm surge to sustain the daily needs of their family. Its also demonstrates that the capacity of these people to protect themselves from the threat is constrained by poor and fragile livelihoods. In the event of a crisis, the study argues that people resort to a range of adjustments on their daily life which is rooted in the strength and diversity of their livelihoods. To reduce people’s vulnerability and enhance capacities to face coastal hazards, the study fosters Community-Based Disaster Risk Reduction with special emphasis to sustainable livelihoods.     

Historical spatial reconstruction of a spawning‐aggregation fishery

Aggregations of individual animals that form for breeding purposes are a critical ecological process for many species, yet these aggregations are inherently vulnerable to exploitation. Studies of the decline of exploited populations that form breeding aggregations tend to focus on catch rate and thus often overlook reductions in geographic range. We tested the hypothesis that catch rate and site occupancy of exploited fish‐spawning aggregations (FSAs) decline in synchrony over time. We used the Spanish mackerel (Scomberomorus commerson) spawning‐aggregation fishery in the Great Barrier Reef as a case study. Data were compiled from historical newspaper archives, fisher knowledge, and contemporary fishery logbooks to reconstruct catch rates and exploitation trends from the inception of the fishery. Our fine‐scale analysis of catch and effort data spanned 103 years (1911–2013) and revealed a spatial expansion of fishing effort. Effort shifted offshore at a rate of 9.4 nm/decade, and 2.9 newly targeted FSAs were reported/decade. Spatial expansion of effort masked the sequential exploitation, commercial extinction, and loss of 70% of exploited FSAs. After standardizing for improvements in technological innovations, average catch rates declined by 90.5% from 1934 to 2011 (from 119.4 to 11.41 fish/vessel/trip). Mean catch rate of Spanish mackerel and occupancy of exploited mackerel FSAs were not significantly related. Our study revealed a special kind of shifting spatial baseline in which a contraction in exploited FSAs occurred undetected. Knowledge of temporally and spatially explicit information on FSAs can be relevant for the conservation and management of FSA species.     

The effect of mercury on trees and their mycorrhizal fungi

The Oak Ridge Reservation, established in 1942, was the designated site for the construction of the atomic bomb. During a 20-year period from 1944 to 1963 radioactive and toxic chemical pollutants, especially mercury compounds were released into the surrounding waterways. Tree diversity and mycorrhizal presence and abundance were analyzed in the mercury-contaminated floodplains of East Fork Poplar Creek Oak Ridge (EFPC) (Tennessee). A subsequent greenhouse study was conducted to assess the phytotoxic effects of different mercuric solutions on Platanus occidentalis (American Sycamore), inoculated with soils from EFPC. Total soil mercury in the field had no effect on tree diversity. Organic species of mercury proved to be more toxic than inorganic species of mercury and soil inoculants from EFPC had no protective effects against Hg toxicity in our greenhouse study. Comparison of the effects of mercury contamination in our field and greenhouse studies was difficult due to uncontrolled factors.