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Abstract Local-scale studies have shown that an overabundance of Cervidae species (deer, elk, moose) impacts forest bird communities. Through meta-analysis, we provide a generalized estimate of the overall direction and magnitude of the indirect effects overabundant cervids have on avian species. We conducted 2 distinct meta-analyses that synthesized data on 130 bird species collected from 17 publications. These analyses compared bird species’ population abundance and/or species richness at sites with overabundant cervids to sites with lower cervid abundance or without cervids. We evaluated whether the impacts of overabundant cervids are generally in the same direction (positive, negative) across avian species and locations and if effects vary in magnitude according to avian nesting location and foraging habitat. We found that where cervids were overabundant, there was a significant decrease in mean bird population abundance and species richness. Species that nest in trees, shrubs, and on the ground showed the largest decreases in abundance, as did species whose primary habitat is forest and open woodland and species that are primarily insectivores or omnivores. We did not find significant decreases in abundance for avian species that nest in cavities, whose primary habitat is grassland or scrub, nor for species that mainly eat seeds. Our results indicate that overabundant cervids, likely through their direct effects on vegetation and indirect effects on insects and forest birds, negatively impact individual bird populations and decrease overall avian species richness.
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Is species richness mediated by functional and genetic divergence? A global analysis in birds
1. Unravelling why species richness shows such dramatic spatial variation is an ongoing challenge. Common to many theories is that increasing species richness (e.g. with latitude) requires a compensatory trade-off on an axis of species' ecology. Spatial variation in species richness may also affect genetic diversity if large numbers of coexisting, related species result in smaller population sizes. 2. Here, we test whether increasing species richness results in differential occupation of morphospace by the constituent species, or decreases species' genetic diversity. We test for two potential mechanisms of morphological accommodation: denser packing in ecomorphological space, and expansion of the space. We then test whether species differ in their nucleotide diversity depending on allopatry or sympatry with relatives, indicative of potential genetic consequences of coexistence that would reduce genetic diversity in sympatry. We ask these questions in a spatially explicit framework, using a global database of avian functional trait measurements in combination with >120,000 sequences downloaded from GenBank. 3. We find that higher species richness within families is not systematically correlated with either packing in morphological space or overdispersion but, at the Class level, we find a general positive relationship between packing and species richness, but that points sampled in the tropics have comparatively greater packing than temperate ones relative to their species richness. We find limited evidence that geographical co-occurrence with closely related species or tropical distributions decreases nucleotide diversity of nuclear genes; however, this requires further analysis. 4. Our results suggest that avian families can accumulate species regionally with minimal tradeoffs or cost, implying that external biotic factors do not limit species richness.
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- Award ID(s):
- 1633535
- PAR ID:
- 10359592
- Date Published:
- Journal Name:
- Functional Ecology
- ISSN:
- 0269-8463
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/1365-2435.14153
