The Challenges of Studying Vertebrates in Habitat Treatment Plots

Abstract

The Challenges of Studying Vertebrates in Habitat Treatment Plots Managers need information about effects of environmental change on populations of species. Such data often come from experiments where habitat components are manipulated and subsequent changes in population size, productivity, or behavior are measured. Research biologists, however, are often reluctant, or unable, to publish data about responses of uncommon organisms because small sample sizes reduce strength of inference as statistical power declines. These challenges to inference are real, but should not completely eliminate access to data that could be valuable to managers [1]. In general, many managers would say some data is better than no data at all. They would prefer to have some data that could be added to their own personal knowledge of a system than to have no data at all. Multiple factors influence habitat management decisions, so managers are typically keen to acquire all data they can before making decisions, even if those data are sparse. An example of this situation comes from attempts to study responses of terrestrial vertebrates to habitat manipulation experiments designed to study plants. Such experiments are often quite expensive so many are designed to incorporate just enough area and replication to identify responses of plants, but are typically too small to ensure that sample sizes of wideranging mammals, birds, reptiles, and amphibians are large enough to allow population or demographic responses to be measured with confidence. Analytical methods that estimate habitat-associated changes in population size, reproductive success, or survival are often quite data hungry. When samples are small, confidence intervals around estimated parameters are inevitably quite large, leading to a reduction in power to detect treatment effects.

Landscape Context Mediates Avian Habitat Choice in Tropical Forest Restoration

“…Such a bias would strengthen our conclusion that relative abundance is greater in plantations, however, this result does not denote a successful restoration of the bird community per se in any particular treatment [101] . Many habitat manipulation studies, including this one, are too small to reliably detect differences in population or demographic variables needed to infer community restoration, but they still contain useful information [71] .…”

“…Spatial non-independence was therefore modeled as a nested random effect. Finally, studies evaluating vertebrate responses to small habitat manipulations have unique challenges and should be explicit about the inferences that can be made [71] . We do not assume that any birds complete their life cycle within the restoration sites that we studied or that these interventions have restored bird communities per se.…”

Large canopy and animal‐dispersed species facilitate natural regeneration in tropical forest restoration

“…We recognize that both seed dispersers and regenerating seedlings may be affected not only by the traits of the tree sampled, but also by surrounding trees and environmental conditions. For example, bird visitation, seed rain, and natural regeneration are influenced by the size of tree clusters, as well as canopy cover, and not only by traits of a single tree (Fink et al 2009; Robinson 2010; Zahawi et al 2013). For example, Zahawi et al (2013) observed that large tree clusters (144 m 2 ) had more seedlings established than smaller clusters (16 m 2 ) indicating the importance of the joint canopy cover of several trees to facilitate recruitment in tropical forests under restoration.…”

Lianas maintain insectivorous bird abundance and diversity in a neotropical forest

“…Yet since the 2011-2013 surveys all occurred during peak activity period of January-April, it is clear that the liana-removal manipulation was responsible for the abrupt change in avian abundance and diversity. Like most habitat manipulation experiments, plot sizes were small relative to the home ranges of most of the bird species that we encountered (Robinson 2010). Therefore, changes in bird density, diversity, and composition are likely an accurate reflection of the local changes in habitat use within the plots.…”