Niche partitioning is an important mechanism for allowing ecologically similar species to coexist, contributing to biodiversity and the functioning of ecological communities. Species partition niches ...by taking advantage of environmental heterogeneity. However, niche partitioning and species coexistence investigations often do not include intraspecific variation or individual differences like sex and body size even though these factors can have important ecological consequences. Such intrapopulation factors can reduce the number of individuals among species that overlap in resource use and potentially facilitate coexistence. Using stable isotopes (δ
13
C and δ
15
N), we quantified dietary differences among three ecologically similar, sympatric watersnake species:
Nerodia erythrogaster
,
N. rhombifer
and
N. sipedon
. Additionally for each species, we determined intraspecific dietary patterns and determined how those within-species patterns may contribute to dietary niche partitioning among species.
Nerodia erythrogaster
fed more on terrestrial prey, while
N. rhombifer
fed at higher trophic levels. Females across species fed at higher trophic levels than did males, and isotopic variance differed between the sexes in
N. sipedon
. Larger watersnakes foraged at higher trophic levels and fed more on terrestrial prey. Each watersnake species had a distinct diet that overlapped to some degree with the other species’ diets, but these diets varied both between sexes and among size groups within species. This inter- and intraspecific dietary variation can facilitate species coexistence by reducing the number of individuals from all species that use the same resources. Intraspecific variation can add important and nuanced layers to the evolution of species coexistence, and research on interspecific niche relationships needs to increasingly consider the effects of these intraspecific variations.
Abstract
Investigating dietary resource utilization and head morphology of gape-limited predators can provide a basis for understanding interspecific competition and species coexistence. For ...sympatric species, convergence of head morphology can indicate similar prey or foraging strategies while divergence can suggest competition, resource partitioning or expansion into new habitats. Sexual dimorphism can further complicate the head morphology-diet relationship by potentially reducing intraspecific competition. To understand the relationship between head morphology and diet, we studied three sympatric species, the plain-bellied (Nerodia erythrogaster), diamondback (N. rhombifer), and northern (N. sipedon) watersnakes in western Kentucky. All three species inhabit similar wetlands and feed on amphibians and fishes. The anurophagous plain-bellied watersnakes had longer, narrower heads that likely allow snakes to capture anuran metamorphs and froglets while facilitating movement through dense vegetation. The piscivorous diamondback watersnake had a wider head, which would enhance contact with prey in this open-mouth forager, and smaller interocular distance, resulting in dorsally placed eyes that facilitate seeing fish prey from below. The mostly piscivorous northern watersnake had an intermediate, generalized head shape, which may reflect the typically wide diet range of this species. Head shape did not differ between snake sexes but diamondback and northern females had larger heads than males and fed more frequently on fishes. The relationship between head morphology and diet highlights potential interspecific and intersexual competition and aids in the understanding of species coexistence patterns.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The longleaf pine (
Pinus palustris) forest, one of the most diverse yet endangered ecosystems in North America, has received considerable interest from conservation biologists. Longleaf pine ...ecosystem management focuses on maintaining open mature pine savanna with reduced hardwood levels. Sherman's fox squirrel (
Sciurus niger shermani), a near obligate species of the open mature longleaf pine forest and a species of concern, relies on embedded hardwood trees for food and shelter but avoids closed-canopy hardwood forests. So where is the middle ground of hardwood importance to the squirrel? Ecosystem-scale conservation focusing on intensive removal of hardwoods from within the longleaf pine matrix, may negatively impact Sherman's fox squirrels. To understand the importance of hardwoods to Sherman's fox squirrels, we conducted a radio telemetry study focusing on habitat components within fox squirrel home ranges. Our results suggest a range of acceptance to the ratio of mature pine to hardwood within longleaf pine forests with an 80% estimated probability of home range use when canopy cover is comprised of 88.2% mature pine savanna to 11.8% hardwood cover. Conservation and restoration efforts should maintain individual mature hardwood trees and small patches within the longleaf pine forest ecosystem to benefit Sherman's fox squirrel.
Fox squirrel (Sciurus niger) populations are declining in the southeastern United States, presumably as a function of habitat loss. Because the ecology of southeastern subspecies of fox squirrels ...differs greatly from their well-studied midwestern relatives, habitat studies of midwestern fox squirrels are of limited use for managing southeastern subspecies. Therefore, we initiated a radiotelemetry study to evaluate habitat use of fox squirrels (n = 101) in southwestern Georgia, USA. Our results indicated that sex of fox squirrels and season did not affect habitat use and that fox squirrels did not display habitat selection within the home range. However, when selecting a home range, fox squirrels preferred mature pine (Pinus spp.) and mixed pine–hardwood forests and avoided hardwood forests. To provide fox squirrel habitat in southeastern pine landscapes, management strategies should maintain mixtures of mature longleaf pine (P. palustris) and mature mixed pine–hardwood forests.
Food plots are often used to enhance habitat for game species within forested systems, but food plots also create edge within the forested matrix that may attract nest predators. Because little ...information exists regarding how food plots affect nest predation, we examined predation rates on artificial nests placed in 30 food plots (0.70–13.0
ha). We determined that four spatial variables and one temporal variable were important predictors of predator use of food plots. Predators used forested edges more intensively than fallow strips within food plots and small food plots with short perimeters more intensively than large food plots with long perimeters. As food plots became more irregularly shaped, intensity of predator use increased. Last, predators used food plots more intensively during the early nesting season (May) than during the later nesting season (July). Because many bird species nest along food plot/forest ecotones or in native vegetation within periodically disturbed sites, managers should consider food plot designs that reduce encounter rates between nesting birds and their predators.
To better understand bird response to percentage and pattern of woody cover in agricultural areas, we recorded richness and abundance of breeding birds in 500-m transects along 18 wooded streams in ...southeastern Nebraska. Transects had differing amounts of woody cover in the surrounding landscape (∼2-39%) out to distances of 500, 1,000, and 2,000 m. We grouped bird species as woodland (22 species) or edge (30 species) and analyzed results from the 1999 and 2000 breeding seasons using information theoretic methods. Richness of the woodland group increased with percentage of woody cover out to 500 m, but abundance did not change. In contrast, richness of the edge group was not affected by landscape variables, but abundance increased as percentage of woody cover decreased out to 1,000 m. Eight species increased in abundance and 5 decreased with increasing percentage of woody cover in the landscape out to distances of 500, 1,000, or 2,000 m. The great crested flycatcher (Myiarchus crinitus) was not present at sites with ≤14.7% woody cover in the surrounding landscape out to 500 m, and the eastern woodpewee (Contopus virens), except for one site, was not present at sites with ≤24% woody cover out to 500 m. The Baltimore oriole (Icterus galbula) and warbling vireo (Vireo gilvus) apparently responded to the presence of large eastern cottonwood (Populus deltoides) trees. Management for a diverse avifauna in fragmented agricultural landscapes should include both local- and landscape-scale variables, including the amoung and pattern of woody cover in the surrounding landscape.
