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6 results for “niche variation hypothesis”
Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis
1. The niche variation hypothesis (NVH) predicts that populations with wider niches are phenotypically more variable than populations with narrower niches, which is frequently used to explain diversifying processes such as ecological release. However, not all empirical evidence supports the NVH. Furthermore, a relationship between population phenotypic variation and niche width can be caused by sexual selection or environmental gradients, which should be carefully considered along with competition in explaining niche variation. 2. In this study we used eight populations of a generalist passerine species, Paradoxornis webbianus (vinous-throated parrotbill), to test the NVH. We assessed evidence of ecological sexual dimorphism and environmental gradients in bill morphology of P. webbianus. A total of 170 P. webbianus from eight sites ranging 24-2,668 m in altitude were included in this study. We used two principal components to quantify bill morphology, one describes bill size and the other describe bill slenderness. We used stable carbon and nitrogen isotope values of bird feathers to quantify trophic positions, and we estimated population trophic niche width using Bayesian standardized ellipse area. 3. Paradoxornis webbianus with larger and more slender bills fed at higher trophic levels and population trophic niche width tended to increase with bill size variation, supporting the NVH. The males had larger bills and marginally higher nitrogen isotope values than the females, suggesting ecological sexual dimorphism. Despite a positive correlation between bill size and wing length indicating sexual selection for larger male size, only three of the eight populations showed both male-biased bill size and male-biased wing length. Sexual dimorphism explained 13%-64% of bill size variation across sites, suggesting its role in niche variation could vary greatly among populations. The variation in bill slenderness in P. webbianus increased with elevation. However, neither bill size variation nor trophic niche width changed with elevation. Therefore, environmental gradients that could be reflected in the elevation are not likely to drive the observed morphological and niche variation. 4. This study provides an empirical case for the NVH and highlights the importance to investigate sexual dimorphism and environmental gradients in the studies of niche dynamics.
Data from: Individual contribution to niche expansion in amphibians: A test of the niche variation hypothesis
<p>The niche variation hypothesis (NVH) suggests that populations released from competition are able to expand their realized ecological niche (Van valen 1965; Bolnick et al. 2007). This increase in total niche width (TNW) can arise by i) increasing heterogeneity among individuals' niche through individual specialization, i.e. inter-individual variation in resource use, (IS – Bolnick et al., 2002; 2003) occurring when different individuals of a population use a subset of the population's resource pool, or ii) by expanding the niche of all individuals within the population (Bolnick et al. 2007). Although several morphological and phenotypical studies have confuted the NVH (e.g. Meiri et al. 2005), there is generally strong support for this hypothesis when behavioural or ecological traits are considered, and in particular when the trophic niche is measured at the individual level (Bolnick et al. 2007; Maldonado et al., 2017). In this study our primary aim is to corroborate the NVH, providing robust evidence for a significant and positive relationship between population TNW and IS in amphibian populations, at a global scale.</p>
Data from: Individual contribution to niche expansion in amphibians: A test of the niche variation hypothesis
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Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis
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Data from: A test of the niche variation hypothesis in a ruminant herbivore
<p class="MsoPlainText">1. Despite the shared prediction that the width of a population's dietary niche expands as food becomes limiting, the Niche Variation Hypothesis (NVH) and Optimal Foraging Theory (OFT) offer contrasting views about how individuals alter diet selection when food is limited.</p> <p class="MsoPlainText">2. Classical OFT predicts that dietary preferences do not change as food becomes limiting, so individuals expand their diets as they compensate for a lack of preferred foods. In contrast, the NVH predicts that among-individual variation in cognition, physiology, or morphology create functional trade-offs in foraging efficiency, thereby causing individuals to specialize on different subsets of food.</p> <p class="MsoPlainText">3. To evaluate (a) the predictions of the NVH and OFT and (b) evidence for physiological and cognitive-based functional trade-offs, we used DNA microsatellites and metabarcoding to quantify the diet, microbiome, and genetic relatedness (a proxy for social learning) of 218 moose (Alces alces) across six populations that varied in their degree of food limitation.</p> <p class="MsoPlainText">4. Consistent with both the NVH and OFT, dietary niche breadth increased with food limitation. Increased diet breadth of individuals—rather than increased diet specialization—was strongly correlated with both food limitation and dietary niche breadth of populations, indicating that moose foraged in accordance with OFT. Diets were not constrained by inheritance of the microbiome or inheritance of diet selection, offering support for the little-tested hypothesis that functional trade-offs in food use (or lack thereof) determine whether populations adhere to the predictions of the NVH or OFT.</p> <p class="MsoPlainText">5. Our results indicate that both the absence of strong functional trade-offs and the digestive physiology of ruminants provide contexts under which populations should forage in accordance with OFT rather than the NVH. Also, because dietary niche width increased with increased food limitation, OFT and the NVH provide theoretical support for the notion that plant-herbivore interaction networks are plastic rather than static, which has important implications for understanding interspecific niche partitioning. Lastly, because population-level dietary niche breadth and calf recruitment are correlated, and because calf recruitment is a proxy for food limitation, our work demonstrates how diet data can be employed to understand a populations' proximity to carrying capacity.</p>
Data from: A test of the niche variation hypothesis in a ruminant herbivore
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