Ecological Parameters (ecological + parameter)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Ecological parameters of the leaf-litter frog community of an Atlantic Rainforest area at Ilha Grande, Rio de Janeiro state, Brazil

Abstract The Atlantic Rainforest originally covered much of the Brazilian coast and is now reduced to approximately only 7% of its original area. Data on abundance distribution and microhabitat characteristics of anuran amphibians living on the forest floor leaf litter in the Atlantic Rainforest are scarce. In this study, we analysed the effect of litter depth and structure on the abundance and species richness of leaf-litter frogs in an area of Atlantic Rainforest at Ilha Grande, Rio de Janeiro State, south-eastern Brazil. We performed monthly samples (nocturnal and diurnal) from August 1996 to October 1997 using small (2 m × 1 m) plots. We sampled 234 plots, totalling 468 m2 of forest leaf litter. We estimated leaf-litter depth and the proportion of leaves in the plot and tested their effect on the total abundance of frogs and species richness using multiple regression analysis. We found 185 frogs from eight species: Brachycephalus (=Psyllophryne) didactylus (Izecksohn, 1971) (Brachycephalidae), Dendrophryniscus brevipollicatus Jiménez de la Espada 1871 (Bufonidae), Adenomera marmorata Steindachner 1867, Eleutherodactylus parvus (Girard 1853), Eleutherodactylus guentheri (Steindachner 1864), Eleutherodactylus binotatus (Spix 1824) and Zachaenus parvulus (Girard 1853) (Leptodactylidae), and Chiasmocleis sp. (Microhylidae). Brachycephalus didactylus was the most abundant species, with 91 individuals, whereas Dendrophryniscus brevipollicatus was the rarest, with two individuals. Mean litter depth and the proportion of leaves in the leaf litter were significantly related to frog abundance (R2 = 0.17; F2,107 = 10.779; P = 0.0001) and species richness (R2 = 0.11; F2,107 = 6.375; P = 0.002) indicating that microhabitat characteristics may affect local distribution and abundance of frogs in the forest floor. [source]

Common birds facing global changes: what makes a species at risk?

Romain Julliard
Abstract Climate change, habitat degradation, and direct exploitation are thought to threaten biodiversity. But what makes some species more sensitive to global change than others? Approaches to this question have relied on comparing the fate of contrasting groups of species. However, if some ecological parameter affects the fate of species faced with global change, species response should vary smoothly along the parameter gradient. Thus, grouping species into few, often two, discrete classes weakens the approach. Using data from the common breeding bird survey in France , a large set of species with much variability with respect to the variables considered , we show that a quantitative measure of habitat specialization and of latitudinal distribution both predict recent 13 year trends of population abundance among 77 terrestrial species: the more northerly distributed and the more specialized a species is, the sharper its decline. On the other hand, neither hunting status, migrating strategy nor body mass predicted population growth rate variation among common bird species. Overall, these results are qualitatively very similar to the equivalent relationships found among the British butterfly populations. This constitutes additional evidence that biodiversity in Western Europe is under the double negative influence of climate change and land use change. [source]

Empirical comparison of density estimators for large carnivores

Martyn E. Obbard
Summary 1. Population density is a critical ecological parameter informing effective wildlife management and conservation decisions. Density is often estimated by dividing capture,recapture (C,R) estimates of abundance () by size of the study area, but this relies on the assumption of geographic closure , a situation rarely achieved in studies of large carnivores. For geographically open populations is overestimated relative to the size of the study area because animals with only part of their home range on the study area are available for capture. This bias (,edge effect') is more severe when animals such as large carnivores range widely. To compensate for edge effect, a boundary strip around the trap array is commonly included when estimating the effective trap area (). Various methods for estimating the width of the boundary strip are proposed, but / estimates of large carnivore density are generally mistrusted unless concurrent telemetry data are available to define. Remote sampling by cameras or hair snags may reduce study costs and duration, yet without telemetry data inflated density estimates remain problematic. 2. We evaluated recently developed spatially explicit capture,recapture (SECR) models using data from a common large carnivore, the American black bear Ursus americanus, obtained by remote sampling of 11 geographically open populations. These models permit direct estimation of population density from C,R data without assuming geographic closure. We compared estimates derived using this approach to those derived using conventional approaches that estimate density as /. 3. Spatially explicit C,R estimates were 20,200% lower than densities estimated as /. AICc supported individual heterogeneity in capture probabilities and home range sizes. Variable home range size could not be accounted for when estimating density as /. 4.Synthesis and applications. We conclude that the higher densities estimated as / compared to estimates from SECR models are consistent with positive bias due to edge effects in the former. Inflated density estimates could lead to management decisions placing threatened or endangered large carnivores at greater risk. Such decisions could be avoided by estimating density by SECR when bias due to geographic closure violation cannot be minimized by study design. [source]

Environmental Predictors of Geographic Variation in Human Mating Preferences

ETHOLOGY, Issue 4 2002
Kevin J. McGraw
Sexual selection theory classically posits consistent and directional mate-preferences for male traits that provide benefits to females. However, flexible mate-choice tactics may persist within a species when males display multiple desirable features that confer different benefits to females under variable environmental conditions. Ecological factors such as population density, resource demand, and sex ratio can influence the value that female animals place on certain male characteristics across mating environments. In this study, I used human mate-preference data from `lonely hearts' advertisements in the newspapers of 23 cities in the USA to assess geographic differences in female preferences for male traits (e.g. physical attributes, resource-holding potential, emotional characteristics, personal interests) in relation to these ecological parameters. I found that females placed more emphasis on the resource-accruing ability of prospective mates in densely populated cities and cities having greater resource demands (higher cost of living). In contrast, women from densely populated or resource-demanding cities placed less emphasis on the emotional aspects or personal interests of males. Preferences for physical features were not environmentally linked, but instead were a function of the degree to which females advertised their own physical attractiveness. Collectively, these results suggest that certain mate-choice criteria employed by women are sensitive to variation in local environmental conditions and that variable levels of resource or mate availability may favor different mating tactics across human populations. [source]


EVOLUTION, Issue 6 2002
Fabio Dercole
Abstract How does the process of life-history evolution interplay with population dynamics? Almost all models that have addressed this question assume that any combination of phenotypic traits uniquely determine the ecological population state. Here we show that if multiple ecological equilibria can exist, the evolution of a trait that relates to competitive performance can undergo adaptive reversals that drive cyclic alternation between population equilibria. The occurrence of evolutionary reversals requires neither environmentally driven changes in selective forces nor the coevolution of interactions with other species. The mechanism inducing evolutionary reversals is twofold. First, there exist phenotypes near which mutants can invade and yet fail to become fixed; although these mutants are eventually eliminated, their transitory growth causes the resident population to switch to an alternative ecological equilibrium. Second, asymmetrical competition causes the direction of selection to revert between high and low density. When ecological conditions for evolutionary reversals are not satisfied, the population evolves toward a steady state of either low or high abundance, depending on the degree of competitive asymmetry and environmental parameters. A sharp evolutionary transition between evolutionary stasis and evolutionary reversals and cycling can occur in response to a smooth change in ecological parameters, and this may have implications for our understanding of size-abundance patterns. [source]

Habitat saturation and the spatial evolutionary ecology of altruism

Abstract Under which ecological conditions should individuals help their neighbours? We investigate the effect of habitat saturation on the evolution of helping behaviours in a spatially structured population. We combine the formalisms of population genetics and spatial moment equations to tease out the effects of various physiological (direct benefits and costs of helping) and ecological parameters (such as the density of empty sites) on the selection gradient on helping. Our analysis highlights the crucial importance of demography for the evolution of helping behaviours. It shows that habitat saturation can have contrasting effects, depending on the form of competition (direct vs. indirect competition) and on the conditionality of helping. In our attempt to bridge the gap between spatial ecology and population genetics, we derive an expression for relatedness that takes into account both habitat saturation and the spatial structure of genetic variation. This analysis helps clarify discrepancies in the results obtained by previous theoretical studies. It also provides a theoretical framework taking into account the interplay between demography and kin selection, in which new biological questions can be explored. [source]


ABSTRACT. We investigate wildlife disease management, in a bioeconomic framework, when the wildlife host is valuable and disease transmission is density-dependent. Disease prevalence is reduced in density-dependent models whenever the population is harvested below a host-density threshold a threshold population density below which disease prevalence declines and above which a disease becomes epidemic. In conventional models, the threshold is an exogenous function of disease parameters. We consider this case and find a steady state with positive disease prevalence to be optimal. Next, we consider a case in which disease dynamics are affected by both population controls and changes in human-environmental interactions. The host-density threshold is endogenous in this case. That is, the manager does not simply manage the population relative to the threshold, but rather manages both the population and the threshold. The optimal threshold depends on the economic and ecological trade-offs arising from the jointly-determined system. Accounting for this endogene-ity can lead to reduced disease prevalence rates and higher population levels. Additionally, we show that ecological parameters that may be unimportant in conventional models that do not account for the endogeneity of the host-density threshold are potentially important when host density threshold is recognized as endogenous. [source]

Body condition does not predict immunocompetence of western pond turtles in altered versus natural habitats

N. Polo-Cavia
Abstract Many authors have addressed the relationship between body condition and ecological parameters in a wide range of studies, suggesting a better fitness in those individuals with higher values of body condition. However, body size and body condition of individuals can vary significantly at the intraspecific level between geographic locations, which is usually explained by phenotypic plasticity or local adaptation. We suggest that a higher body condition per se might not be a good indicator of physiological health status, particularly when comparing populations inhabiting places with different levels of habitat alteration. We examined two populations of the western pond turtle Emys marmorata in the northern part of California's Central Valley, and found that individuals inhabiting a water pollution control plant located on the valley floor had significantly larger body size and higher body condition than those inhabiting an unaltered natural habitat in the foothills. However, turtles from the water pollution control plant did not show a better health status, estimated by comparisons between two immune system variables: T-cell-mediated immune response and heterophil/lymphocyte ratio. Parameters such as body size and body condition might be misleading indicators of health condition, particularly when they are used to estimate health status of populations from habitats with different levels of alteration. We emphasize the importance of using physiological methods in assessing the conservation state of wildlife populations, rather than relying on biometric indices that might miss important effects of alteration. [source]

Wing shape variation in the medium ground finch (Geospiza fortis): an ecomorphological approach

Wing design in birds is subject to a suite of interacting selective pressures. As different performance traits are favoured in different ecological settings, a tight link is generally expected between variation in wing morphology and variation in ecological parameters. In the present study, we document aspects of variation in wing morphology in the medium ground finch (Geospiza fortis) on Isla Santa Cruz in the Galápagos. We compare variation in body size, simple morphometric traits (body mass, last primary length, wing length, wing chord, and wing area) and functional traits (wing loading, aspect ratio and wing pointedness) across years, among populations, and between sexes. Functional traits are found to covary across years with differences in climatic conditions, and to covary among populations with differences in habitat structure. In dry years and arid locations, wing aspect ratios are highest and wings are more pointed, consistent with a need for a low cost of transport. In wet years and cluttered habitats, wing loading is lowest and wings are more rounded, suggesting enhanced capabilities for manoeuvrability. Sexes differ in wing loading, with males having lower wing loadings than females. Superior manoeverability might be favoured in males for efficient territory maintenance. Lastly, in contrast to functional traits, we found little consistent inter-annual or inter-site variation in simple morphometric traits. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 129,138. [source]