Mechanistic and Correlative Models of Ecological Niches

The suite of factors that drives where and under what conditions a species occurs has become the focus of intense research interest. Three general categories of methods have emerged by which researchers address questions in this area: mechanistic models of species’ requirements in terms of environmental conditions that are based on first principles of biophysics and physiology, correlational models based on environmental associations derived from analyses of geographic occurrences of species, and process-based simulations that estimate occupied distributional areas and associated environments from assumptions about niche dimensions and dispersal abilities. We review strengths and weaknesses of these sets of approaches, and identify significant advantages and disadvantages of each. Rather than identifying one or the other as ‘better,’ we suggest that researchers take great care to use the method best-suited to each specific research question, and be conscious of the weaknesses of any method, such that inappropriate interpretations are avoided

Ecological applications of remote sensing data in neotropical rainforests

Understanding species' distributions is a central theme of biodiversity studies. A combination of data derived from moderate and high spectral resolution satellite imagery (vegetation indices and hyperspectral narrow bands, respectively) was used to address questions regarding tree species' distributions, vegetation phenology, and influences on bird seasonal movements in tropical rainforests. Vegetation indices were used in ecological niche modeling to predict movement patterns of a tropical canopy frugivorous bird in Central America: the predicted distributions generally recovered observed non-breeding ranges, but estimated lowland areas for the breeding range, which is restricted to middle elevations. Hyperspectral imagery provided sufficient spectral information to discriminate crowns of five different tree taxa that represent food resources for macaws and peccaries in southeastern Peru. Tree spectra showed significant temporal variation, suggesting that it is possible to study tree phenology remotely. Current and future developments of remote sensing techniques permit regional studies of ecosystem functions and structure

Mechanistic and Correlative Models of Ecological Niches

The suite of factors that drives where and under what conditions a species occurs has become the focus of intense research interest. Three general categories of methods have emerged by which researchers address questions in this area: mechanistic models of species’ requirements in terms of environmental conditions that are based on first principles of biophysics and physiology, correlational models based on environmental associations derived from analyses of geographic occurrences of species, and process-based simulations that estimate occupied distributional areas and associated environments from assumptions about niche dimensions and dispersal abilities. We review strengths and weaknesses of these sets of approaches, and identify significant advantages and disadvantages of each. Rather than identifying one or the other as ‘better,’ we suggest that researchers take great care to use the method best-suited to each specific research question, and be conscious of the weaknesses of any method, such that inappropriate interpretations are avoided

River-Based Surveys for Assessing Riparian Bird Populations: Cerulean Warbler as a Test Case

This is the published version. Copyright Eagle Hill InstituteBirds concentrated in riparian habitats are poorly sampled by traditional survey methods because of the difficulties associated with accessing these habitats. Our objectives were to test the effectiveness of river-based surveys to determine the status, distribution, and relative abundance for riparian bird species in Missouri and northern Arkansas, with special emphasis on Dendroica cerulea (Cerulean Warbler). Our canoe-based surveys revealed an average of 2.3 and 0.8 singing male Cerulean Warblers/river km along the Current River (128 river km surveyed), MO, and the Buffalo National River (96 river km), AR. Nonparametric estimates for repeated surveys of the same river stretches indicate that 69–79% of singing male Cerulean Warblers were detected. However, the bias associated with the estimate methodology and independent song rate data suggest those are conservative estimates. In comparison with land-based point-counts, this river-based protocol offers a quick and efficient assessment of Cerulean Warblers in riparian areas

An evaluation of transferability of ecological niche models

Ecological niche modeling (ENM) is used widely to study species’ geographic distributions. ENM applications frequently involve transferring models calibrated with environmental data from one region to other regions or times that may include novel environmental conditions. When novel conditions are present, transferability implies extrapolation, whereas, in absence of such conditions, transferability is an interpolation step only. We evaluated transferability of models produced using 11 ENM algorithms from the perspective of interpolation and extrapolation in a virtual species framework. We defined fundamental niches and potential distributions of 16 virtual species distributed across Eurasia. To simulate real situations of incomplete understanding of species’ distribution or existing fundamental niche (environmental conditions suitable for the species contained in the study area; N* F ), we divided Eurasia into six regions and used 1–5 regions for model calibration and the rest for model evaluation. The models produced with the 11 ENM algorithms were evaluated in environmental space, to complement the traditional geographic evaluation of models. None of the algorithms accurately estimated the existing fundamental niche (N* F ) given one region in calibration, and model evaluation scores decreased as the novelty of the environments in the evaluation regions increased. Thus, we recommend quantifying environmental similarity between calibration and transfer regions prior to model transfer, providing an avenue for assessing uncertainty of model transferability. Different algorithms had different sensitivity to completeness of knowledge of N* F , with implications for algorithm selection. If the goal is to reconstruct fundamental niches, users should choose algorithms with limited extrapolation when N* F is well known, or choose algorithms with increased extrapolation when N* F is poorly known. Our assessment can inform applications of ecological niche modeling transference to anticipate species invasions into novel areas, disease emergence in new regions, and forecasts of species distributions under future climate conditions

Highly Pathogenic H5N1 Avian Influenza: Entry Pathways into North America via Bird Migration

Given the possibility of highly pathogenic H5N1 avian influenza arriving in North America and monitoring programs that have been established to detect and track it, we review intercontinental movements of birds. We divided 157 bird species showing regular intercontinental movements into four groups based on patterns of movement—one of these groups (breed Holarctic, winter Eurasia) fits well with the design of the monitoring programs (i.e., western Alaska), but the other groups have quite different movement patterns, which would suggest the importance of H5N1 monitoring along the Pacific, Atlantic, and Gulf coasts of North America

A theoretical framework for the ecological role of three-dimensional structural diversity

The three-dimensional (3D) physical aspects of ecosystems are intrinsically linked to ecological processes. Here, we describe structural diversity as the volumetric capacity, physical arrangement, and identity/traits of biotic components in an ecosystem. Despite being recognized in earlier ecological studies, structural diversity has been largely overlooked due to an absence of not only a theoretical foundation but also effective measurement tools. We present a framework for conceptualizing structural diversity and suggest how to facilitate its broader incorporation into ecological theory and practice. We also discuss how the interplay of genetic and environmental factors underpin structural diversity, allowing for a potentially unique synthetic approach to explain ecosystem function. A practical approach is then proposed in which scientists can test the ecological role of structural diversity at biotic–environmental interfaces, along with examples of structural diversity research and future directions for integrating structural diversity into ecological theory and management across scales

Ecological approaches in veterinary epidemiology: mapping the risk of bat-borne rabies using vegetation indices and night-time light satellite imagery

Rabies remains a disease of significant public health concern. In the Americas, bats are an important source of rabies for pets, livestock, and humans. For effective rabies control and prevention, identifying potential areas for disease occurrence is critical to guide future research, inform public health policies, and design interventions. To anticipate zoonotic infectious diseases distribution at coarse scale, veterinary epidemiology needs to advance via exploring current geographic ecology tools and data using a biological approach. We analyzed bat-borne rabies reports in Chile from 2002 to 2012 to establish associations between rabies occurrence and environmental factors to generate an ecological niche model (ENM). The main rabies reservoir in Chile is the bat species Tadarida brasiliensis; we mapped 726 occurrences of rabies virus variant AgV4 in this bat species and integrated them with contemporary Normalized Difference Vegetation Index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The correct prediction of areas with rabies in bats and the reliable anticipation of human rabies in our study illustrate the usefulness of ENM for mapping rabies and other zoonotic pathogens. Additionally, we highlight critical issues with selection of environmental variables, methods for model validation, and consideration of sampling bias. Indeed, models with weak or incorrect validation approaches should be interpreted with caution. In conclusion, ecological niche modeling applications for mapping disease risk at coarse geographic scales have a promising future, especially with refinement and enrichment of models with additional information, such as night-time light data, which increased substantially the model’s ability to anticipate human rabies

Using biotic interactions in broad-scale estimates of species’ distributions

International audienceAim: To examine the combined effect of abiotic and biotic factors on species distri-butions in a marine environment. Specifically, we aim to account for the effects of trophic interactions at broad scales in ecological niche models (ENMs) of sea kraits (Laticauda: Reptilia) by including the potential distribution of food resources as pre-dictor variables.Location: Oceania and Southeast Asia.Methods: First, we outline a simple method to generate biotic interaction variables for ENMs. We then test whether ENMs that include biotic interactions perform bet-ter than ENMs based on abiotic variables only.Results: The models based on biotic interactions (i.e. trophic interactions) and abi-otic variables slightly outperformed the models informed only by abiotic variables. We found a strong relationship between prey species richness and probability of distribution of predator (sea kraits). The models that included potential distributions of prey species as predictor variables showed an increase in proportion of pixels predicted present and a decrease in omission error, compared with models based only on abiotic variables.Main conclusions: Distribution estimates of predator species at broad scales are more accurate if calibration of ENMs includes relevant biotic variables (prey species richness, in this study). Hence, when data are available, biotic variables should be included in ENMs

Refining model estimates of potential species’ distribution to relevant accessible areas

International audienceDispersal is an important, yet overlooked phenomenon when studying species’ distributions using ecologicalniche models (ENMs). Here, we use species’ dispersal limits to evaluate and refine ENM estimates only to theareas accessible to the species within the study region and, thereby, enhance the model interpretations. First,we ran multiple ENMs to estimate the distribution of sea krait species in both marine and terrestrialenvironments. Second, we estimated dispersal of the sea kraits using a cost analysis approach. Finally, weoutline a new approach that combines dispersal models and ENMs with the purpose of estimating theaccessible range when projecting species’ distribution estimates outside the known species range. We foundthat only a small proportion of the area the ENMs were projected over was accessible to sea kraits. Themajority of the suitable areas for sea kraits are within the accessible area. Outside the accessible area, there isonly a very limited suitable area for sea kraits. Our results suggest that when dispersal is taken into account,sea kraits seem to occupy most of their suitable available niche and that they may be unable to colonize muchof the area outside of their dispersal ranges. Using dispersal estimates to refine species’ distribution pre-dictions is a useful tool for refining the area of focus when ENM results are interpreted. Estimating species’dispersal also helps evaluate the ability of the models to predict the species’ distributions in areas that are notaccessible to the species and, hence, the potential commission error represented by overpredictio