Abstract
Delimiting the habitat characteristics describing the environmental conditions required by a species has become a critical tool for predicting organismal responses to environmental change. Grinnell emphasized the effects of environmental factors on the ability of a population to maintain a positive growth rate, yet few studies have included demographic or reproductive data in analyses of the Grinnellian niche. Identifying differences in habitat exploitation patterns in response to structural variation in the environment presents an incomplete description of the ability of species to adapt to changing habitats if demographic traits are not included. We estimated the vegetation characteristics used by individuals within a population of hooded warblers (Setophaga citrina) across a spatial transect that includes three structurally different forest habitats. We predicted individuals should select similar structural characteristics within each habitat and have similar reproductive success across sample sites. In the two years post burn, adults were present but no young fledged indicating the habitat requirements necessary for reproduction were absent in this habitat. We found significant differences in habitat space occupied by individuals in unaltered and harvested habitats. Nesting habitats used by female warblers differed from available habitat. Fledging success was lower in the harvested habitat 10 to 12 years post-harvest. In the harvested habitat, fledging success was greater on mesic slopes but decreased along a habitat gradient to xeric ridgetops, suggesting compensation in habitat use does not ameliorate fitness costs. In contrast, there was no difference in the number of fledged young along this gradient in the unaltered habitat. Based solely on occupancy data, traditional ecological niche models would incorrectly conclude the environmental characteristics found across the three forested habitats are included in the Grinnellian niche of the hooded warbler. However, examination of demographic and environmental data simultaneously allows differentiation between occupied habitat space and niche space.
Highlights
The distribution of species across a landscape depends on the spectrum of both biotic and abiotic factors that result in a stable or positive population growth rate [1,2,3]
The first nonmetric multidimensional scaling (NMDS) axis described a moisture gradient with mesic forest characterized by L. benzoin and canopy Liriodendron tulipifera at one end to xeric forests associated with canopy Q. prinus, Smilax spp., Q. prinus saplings and midstory Acer rubrum at the other (S1 Table and S1 Fig)
The centroids of the habitat space used by males and females in the unaltered and harvested habitats compared to the available habitat suggest differences in the habitat characteristics selected by males and females
Summary
The distribution of species across a landscape depends on the spectrum of both biotic and abiotic factors that result in a stable or positive population growth rate [1,2,3]. Demographic Costs and Habitat Space Occupancy reproduction are components of the Grinnellian niche [6,7] These environmental factors include ambient temperature, precipitation and habitat structure that affect the availability and distribution of resources, which in turn determines the suitability of a habitat for a species and delimits its range [8,9,10,11]. This niche space consists of multiple habitat axes because different environmental characteristics may be needed for different aspects of a species’ life history [2,12]. Some habitats may contain resources along critical axes, such as for foraging, but insufficient resources for other aspects of reproductive success, such as nesting sites, and be a sink habitat [13]
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