Impact Population Persistence Research Articles

Strategic grassland conservation for swift foxes in multi-use landscapes

Grasslands are among the most widely distributed, but most imperiled, biomes on Earth. North American grasslands once covered ~162 million ha prior to European colonization, but only ~30 % of this landcover currently remains due to continued human-modified landscape changes. Strategic conservation of remaining grassland landcover, which considers species-specific habitat requirements, is critical for the persistence of grassland species and has become a global priority. Intact grassland landcover is critical for swift fox (Vulpes velox), a facultative prairie carnivore, and we sought to strategically identify areas where grassland conservation would most impact population persistence in an agro-prairie ecosystem. We modeled site (n = 381) occupancy by swift foxes using three years of camera-trap data (2018–2020) from western Kansas, USA, and integrated known-fate survival information to identify priority native grassland conservation areas. Additionally, we evaluated ownership of our identified priority conservation lands to determine strategies for conservation delivery. Our grassland assessment of two thresholds of predicted swift fox occupancy (≥0.09 [priority] and ≥0.18 [high priority]) identified 2,377,193 ha and 84,420 ha for conservation in Kansas, respectively. Identified conservation areas were overwhelmingly located on privately owned working lands (98 % [priority and high priority]), rather than federal, state, or non-governmental organization owned lands (2 % [priority and high priority]), and highlight the need for using conservation easements and incentive-based programs to promote grassland conservation to private landowners.

Climate Change Alters Sexual Signaling in a Desert-Adapted Frog.

AbstractClimate change is altering species' habitats, phenology, and behavior. Although sexual behaviors impact population persistence and fitness, climate change's effects on sexual signals are understudied. Climate change can directly alter temperature-dependent sexual signals, cause changes in body size or condition that affect signal production, or alter the selective landscape of sexual signals. We tested whether temperature-dependent mating calls of Mexican spadefoot toads (Spea multiplicata) had changed in concert with climate in the southwestern United States across 22 years. We document increasing air temperatures, decreasing rainfall, and changing seasonal patterns of temperature and rainfall in the spadefoots' habitat. Despite increasing air temperatures, spadefoots' ephemeral breeding ponds have been getting colder at most elevations, and male calls have been slowing as a result. However, temperature-standardized call characters have become faster, and male condition has increased, possibly due to changes in the selective environment. Thus, climate change might generate rapid, complex changes in sexual signals with important evolutionary consequences.

Current and time-lagged effects of climate on innate immunity in two sympatric snake species.

Changing environments result in alterations at all levels of biological organization, from genetics to physiology to demography. The increasing frequency of droughts worldwide is associated with higher temperatures and reduced precipitation that can impact population persistence via effects on individual immune function and survival.We examined the effects of annual climate variation on immunity in two sympatric species of garter snakes from four populations in California over a seven‐year period that included the record‐breaking drought.We examined three indices of innate immunity: bactericidal competence (BC), natural antibodies (NABs), and complement‐mediated lysis (CL).Precipitation was the only climatic variable explaining variation in immune function: spring precipitation of the current year was positively correlated to Thamnophis sirtalis BC and NABs, whereas spring precipitation of the previous year was positively correlated to T. elegans BC and NABs. This suggests that T. elegans experiences a physiological time‐lag in response to reduced precipitation, which may reflect lack of capital for investment in immunity in the year following a dry year.In general, our findings demonstrate compelling evidence that climate can influence wild populations through effects on physiological processes, suggesting that physiological indices such as these may offer valuable opportunities for monitoring the effects of climate.

The thermal limits of cardiorespiratory performance in anadromous Arctic char (Salvelinus alpinus): a field-based investigation using a remote mobile laboratory.

Despite immense concern over amplified warming in the Arctic, physiological research to address related conservation issues for valuable cold-adapted fish, such as the Arctic char (Salvelinus alpinus), is lacking. This crucial knowledge gap is largely attributable to the practical and logistical challenges of conducting sensitive physiological investigations in remote field settings. Here, we used an innovative, mobile aquatic-research laboratory to assess the effects of temperature on aerobic metabolism and maximum heart rate (fHmax) of upriver migrating Arctic char in the Kitikmeot region of Nunavut in the central Canadian Arctic. Absolute aerobic scope was unchanged at temperatures from 4 to 16°C, while fHmax increased with temperature (Q10 = 2.1), as expected. However, fHmax fell precipitously below 4°C and it began to plateau above ~ 16°C, reaching a maximum at ~ 19°C before declining and becoming arrhythmic at ~ 21°C. Furthermore, recovery from exhaustive exercise appeared to be critically impaired above 16°C. The broad thermal range (~4–16°C) for increasing fHmax and maintaining absolute aerobic scope matches river temperatures commonly encountered by migrating Arctic char in this region. Nevertheless, river temperatures can exceed 20°C during warm events and our results confirm that such temperatures would limit exercise performance and thus impair migration in this species. Thus, unless Arctic char can rapidly acclimatize or alter its migration timing or location, which are both open questions, these impairments would likely impact population persistence and reduce lifetime fitness. As such, future conservation efforts should work towards quantifying and accounting for the impacts of warming, variable river temperatures on migration and reproductive success.

Hawkmoth Pollination Facilitates Long-distance Pollen Dispersal and Reduces Isolation Across a Gradient of Land-use Change

Land-use change is among the top drivers of global biodiversity loss, which impacts the arrangement and distribution of suitable habitat for species. Population-level effects include increased isolation, decreased population size, and changes to mutualistic and antagonistic interactions. However, the extent to which species are impacted is determined by life history characteristics including dispersal. In plants, mating dynamics can be changed in ways that can negatively impact population persistence if dispersal of pollen and/or seed is disrupted. Long-distance dispersal has the potential to buffer species from the negative impacts of land-use change. Biotic vectors of long-distance dispersal have been less frequently studied, though specific taxa are known to travel great distances. Here, we describe population genetic diversity and structure in a sphingophilous species that is experiencing habitat fragmentation through land-use change, Oenothera harringtonii W. L. Wagner, Stockh. & W. M. Klein (Onagraceae). We use 12 nuclear and four plastid microsatellite markers and show that pollen dispersal by hawkmoths drives high gene flow and low population differentiation despite a range-wide gradient of land-use change and habitat fragmentation. By separating the contributions of pollen and seed dispersal to gene flow, we show that most of the genetic parameters are driven by hawkmoth-facilitated long-distance pollen dispersal, but populations with small, effective population sizes experience higher levels of relatedness and inbreeding. We discuss considerations for conservation efforts for this and other species that are pollinated by long-distance dispersers.

Prior heat accumulation reduces survival during subsequent experimental heat waves

Heat waves, i.e., periods of extremely hot weather, are expected to increase in frequency and duration under climate change. Repeated exposure to thermal stress events such as heat waves can affect population dynamics and even population persistence. Understanding whether recent thermal history bolsters or hinders demographic responses such as survival or growth during heat waves is crucial for predicting population persistence in the face of climate change. We tested for differential mortality following an experimental heat wave in populations of the splash pool copepod, Tigriopus californicus, inhabiting pools that differ in their recent thermal history. We observed differences in survivorship that were correlated with differences in thermal history. Among multiple metrics of thermal history, daily degree-hours (a measure of heat accumulation) best explained heat wave survival such that a higher number of degree-hours resulted in reduced heat wave survival. This finding is consistent with the hypothesis that repeated exposure to sublethal temperatures reduces thermal tolerance. Increasing heat wave intensity and duration, or warmer conditions that increase heat accumulation followed by heat waves may negatively impact population persistence by exacerbating the demographic effects of heat waves. The results of this study emphasize the need to integrate mechanistic physiology within the realm of population ecology to bolster the ability to predict population-level responses to climate change.

Differential influences of local subpopulations on regional diversity and differentiation for greater sage-grouse (Centrocercus urophasianus).

The distribution of spatial genetic variation across a region can shape evolutionary dynamics and impact population persistence. Local population dynamics and among-population dispersal rates are strong drivers of this spatial genetic variation, yet for many species we lack a clear understanding of how these population processes interact in space to shape within-species genetic variation. Here, we used extensive genetic and demographic data from 10 subpopulations of greater sage-grouse to parameterize a simulated approximate Bayesian computation (ABC) model and (i) test for regional differences in population density and dispersal rates for greater sage-grouse subpopulations in Wyoming, and (ii) quantify how these differences impact subpopulation regional influence on genetic variation. We found a close match between observed and simulated data under our parameterized model and strong variation in density and dispersal rates across Wyoming. Sensitivity analyses suggested that changes in dispersal (via landscape resistance) had a greater influence on regional differentiation, whereas changes in density had a greater influence on mean diversity across all subpopulations. Local subpopulations, however, varied in their regional influence on genetic variation. Decreases in the size and dispersal rates of central populations with low overall and net immigration (i.e. population sources) had the greatest negative impact on genetic variation. Overall, our results provide insight into the interactions among demography, dispersal and genetic variation and highlight the potential of ABC to disentangle the complexity of regional population dynamics and project the genetic impact of changing conditions.

Allee effects and resilience in stochastic populations

Allee effects, or positive functional relationships between a population’s density (or size) and its per unit abundance growth rate, are now considered to be a widespread if not common influence on the growth of ecological populations. Here we analyze how stochasticity and Allee effects combine to impact population persistence. We compare the deterministic and stochastic properties of four models: a logistic model (without Allee effects), and three versions of the original model of Allee effects proposed by Vito Volterra representing a weak Allee effect, a strong Allee effect, and a strong Allee effect with immigration. We employ the diffusion process approach for modeling single-species populations, and we focus on the properties of stationary distributions and of the mean first passage times. We show that stochasticity amplifies the risks arising from Allee effects, mainly by prolonging the amount of time a population spends at low abundance levels. Even weak Allee effects become consequential when the ubiquitous stochastic forces affecting natural populations are accounted for in population models. Although current concepts of ecological resilience are bound up in the properties of deterministic basins of attraction, a complete understanding of alternative stable states in ecological systems must include stochasticity.

Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs.

Human-generated noise has profoundly changed natural soundscapes in aquatic and terrestrial ecosystems, imposing novel pressures on ecological processes. Despite interest in identifying the ecological consequences of these altered soundscapes, little is known about the sublethal impacts on wildlife population health and individual fitness. We present evidence that noise induces a physiological stress response in an amphibian and impairs mate attraction in the natural environment. Traffic noise increased levels of a stress-relevant glucocorticoid hormone (corticosterone) in female wood frogs (Lithobates sylvaticus) and impaired female travel towards a male breeding chorus in the field, providing insight into the sublethal consequences of acoustic habitat loss. Given that prolonged elevated levels of corticosterone can have deleterious consequences on survival and reproduction and that impaired mate attraction can impact population persistence, our results suggest a novel pathway by which human activities may be imposing population-level impacts on globally declining amphibians.

Glycogen, not dehydration or lipids, limits winter survival of side-blotched lizards (Uta stansburiana)

Climate change is causing winters to become milder (less cold and shorter). Recent studies of overwintering ectotherms have suggested that warmer winters increase metabolism and decrease winter survival and subsequent fecundity. Energetic constraints (insufficient energy stores) have been hypothesized as the cause of winter mortality but have not been tested explicitly. Thus, alternative sources of mortality, such as winter dehydration, cannot be ruled out. By employing an experimental design that compared the energetics and water content of lizards that died naturally during laboratory winter with those that survived up to the same point but were then sacrificed, we attempt to distinguish among multiple possible causes of mortality. We test the hypothesis that mortality is caused by insufficient energy stores in the liver, abdominal fat bodies, tail or carcass or through excessive water loss. We found that lizards that died naturally had marginally greater mass loss, lower water content, and less liver glycogen remaining than living animals sampled at the same time. Periodically moistening air during winter reduced water loss, but this did not affect survival, calling into question dehydration as a cause of death. Rather, our results implicate energy limitations in the form of liver glycogen, but not lipids, as the primary cause of mortality in overwintering lizards. When viewed through a lens of changing climates, our results suggest that if milder winters increase the metabolic rate of overwintering ectotherms, individuals may experience greater energetic demands. Increased energy use during winter may subsequently limit individual survival and possibly even impact population persistence.

Parasites and pathogens in wild populations of water voles (Arvicola amphibius) in the UK

The water vole (Arvicola amphibius) is Britain’s most endangered mammal, having gained protection under Schedule 5 of the Wildlife and Countryside Act in 2008. We present an overview of a range of naturally occurring pathogens and parasites in this rare species, which might negatively impact population persistence for small or declining populations. Wild water voles were live-captured in 2004 and 2006 from sites throughout the UK and were screened for a range of pathogens. These included: Puumala virus, Campylobacter spp., Escherichia coli, Salmonella enterica, Leptospira spp., Bartonella spp., Toxoplasma gondii, Giardia spp., Cryptosporidium spp., Babesia microti and Trypanosoma spp. E. coli was the most prevalent with 46/74 (62.2%; 95% CI, 51–73) individuals infected. One vole was co-infected with seven different pathogens whilst 20% of individuals were pathogen-free.

Direct and indirect effects of climate change on a prairie plant community.

BackgroundClimate change directly affects species by altering their physical environment and indirectly affects species by altering interspecific interactions such as predation and competition. Recent studies have shown that the indirect effects of climate change may amplify or counteract the direct effects. However, little is known about the the relative strength of direct and indirect effects or their potential to impact population persistence.Methodology/Principal FindingsWe studied the effects of altered precipitation and interspecific interactions on the low-density tiller growth rates and biomass production of three perennial grass species in a Kansas, USA mixed prairie. We transplanted plugs of each species into local neighborhoods of heterospecific competitors and then exposed the plugs to a factorial manipulation of growing season precipitation and neighbor removal. Precipitation treatments had significant direct effects on two of the three species. Interspecific competition also had strong effects, reducing low-density tiller growth rates and aboveground biomass production for all three species. In fact, in the presence of competitors, (log) tiller growth rates were close to or below zero for all three species. However, we found no convincing evidence that per capita competitive effects changed with precipitation, as shown by a lack of significant precipitation × competition interactions.Conclusions/SignificanceWe found little evidence that altered precipitation will influence per capita competitive effects. However, based on species' very low growth rates in the presence of competitors in some precipitation treatments, interspecific interactions appear strong enough to affect the balance between population persistence and local extinction. Therefore, ecological forecasting models should include the effect of interspecific interactions on population growth, even if such interaction coefficients are treated as constants.

Persistence and local extinctions of endangered lizardUma inornataon isolated habitat patches

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 3:61-68 (2007) - doi:10.3354/esr003061 Persistence and local extinctions of endangered lizard Uma inornata on isolated habitat patches Cameron W. Barrows*, Michael F. Allen Center for Conservation Biology, University of California Riverside, Riverside, California 92521-0334, USA *Email: cbarrows@ucr.edu ABSTRACT: Occupancy and persistence in naturally isolated habitat patches were analyzed to evaluate patterns of local extinction of an endangered species, the Coachella Valley fringe-toed lizard Uma inornata. We examined 4 parameters: (1) habitat quality, (2) patch size, (3) patch connectivity, and (4) drought. The Coachella Valley in southern California’s Colorado Desert has a strong west–east gradient, with drier and more persistent drought conditions in the east. The distribution of habitats along this gradient was the best single factor explaining patch occupancy over 14 yr. Drought and patch size provided the best multivariate model. When the westernmost habitat patches were analyzed alone, patch size was the only statistically significant variable. Our results show how conservation planning criteria for species of concern can differ within a species’ range. In this instance, patches located in the eastern part of the valley may need to be much larger than those in the more mesic west. Applying one minimum habitat size criteria for conservation efforts throughout the lizards’ range could result in either not protecting viable populations (e.g. in the west) or spending limited conservation funds on protecting non-sustainable populations in the east (if the minimum size was too small). Identifying gradients that may impact population persistence and extinction across landscapes is an important step in effective conservation planning. KEY WORDS: Patch size · Persistence · Extinction · Drought · Uma inornata · Conservation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 3, No. 1. Online publication date: May 30, 2007 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2007 Inter-Research.

Scale‐dependent interactions between intrinsic and extrinsic processes reduce variability in protist populations

AbstractInteractions between intrinsic processes and extrinsic fluctuations can positively impact population persistence in ways often not predicted by classic ecological models. These interactions only arise when the intrinsic and extrinsic processes operate on the proper relative scales in time or space. Both metapopulation theory and resonance/attenuation theory suggest that interactions which lower population variability will occur when the intrinsic and extrinsic process occur on similar time scales. I performed an aquatic protist microcosm experiment to investigate how the relative frequencies of extrinsic density perturbations and intrinsic resource pulses impacted population variability. Population variability was lowest in the treatments of intermediate frequency, in which the extrinsic fluctuations and intrinsic processes were on the same time scale. This result is consistent with general theoretical predictions, and empirically documents the importance of considering scale in interactions between intrinsic and extrinsic processes that positively impact population persistence.

Reintroduction programmes: genetic trade‐offs for populations

AbstractReintroductions of captive‐managed animals are a vital tool for the conservation of populations and species extinct in the wild. Because genetic diversity may impact population persistence, the genetic composition of reintroduced and captive populations is critical. For captive‐managed species with known pedigrees, individual animals can be selected to create reintroduced populations with specific genetic compositions. Five genetic and demographic strategies for selecting animals were tested on four species. Selection strategies were based on criteria identified in field and theoretical studies. Simulated reintroductions of animals from captive‐breeding programmes created a genetic conflict. Among the different strategies, increases in the genetic diversity of one subpopulation were negatively correlated with changes in the genetic diversity of the other subpopulation. For example, the release of genetically over‐represented animals was the most beneficial strategy for a captive‐breeding programme, but provided the least genetic diversity for the reintroduced population. However, gains and losses in genetic diversity between populations varied with different selection criteria and different population structures. Because captive‐breeding histories vary for each species, changes in genetic composition cannot be accurately predicted and no one strategy is universally optimal. Thus, genetic trade‐offs must be assessed for each population relative to specific programme goals.