Incidence, mechanisms, and consequences of adaptive habitat selection by the dickcissel (Spiza americana)

Most animals display preferences when faced with the choice of habitats in which to settle. A key question that arises from these behaviors is whether preferences represent adaptive habitat selection—do animals occupying preferred habitats incur fitness benefits? A prediction based on natural selection suggests that preferences should increase fitness, but this prediction is not always supported. Several factors may cause preference-fitness mismatches, including temporal variability of variables driving reproductive success, tradeoffs across spatial scales or among fitness components, and anthropogenic changes disrupting historic relationships between habitat preferences and habitat quality. This dissertation presents three studies I conducted on the habitat preferences and reproductive success of dickcissels (Spiza americana) in the Grand River Grasslands of southern Iowa. I first tested for signals of adaptive habitat selection, examining whether male and female birds’ preferences among territories and larger habitat patches improve their ability to attract mates, avoid parasitism by brown-headed cowbirds (Molothrus ater), and produce robust offspring. Dickcissels engaged in adaptive habitat selection in some respects—such as preferring territories associated with high offspring condition and patches where parasitism was infrequent—but there was strong variation across sexes, spatial scales, years, and reproductive components. Next, I examined whether dickcissels used vegetation cues to select high-quality habitats. I measured multiple vegetation features in territories and patches and compared these to dickcissel habitat preferences and fitness metrics. Although dickcissels preferred specific vegetation features (again, with variation across sexes and scales), and specific vegetation features were associated with fitness (again, with variation across reproductive metrics), I found limited evidence that vegetation mediated adaptive habitat selection. Finally, I further studied the impacts of vegetation on dickcissel reproduction by focusing on the relative impacts of human-altered habitat components (invasive plants and broad-scale land cover) on nest survival and parasitism. I found that an invasive grass common throughout the Midwest region (tall fescue, Schedonorus arundinaceus) reduced nest survival and increased parasitism, whereas increasing woodland cover in the landscape reduced parasitism. In these studies, I illuminated proximate and ultimate forces shaping the reproductive ecology of dickcissels. I demonstrated that habitat preferences—and thus the spatiotemporal dynamics of population distributions—benefit specific components of reproductive success at particular spatial scales, while benefits to other reproductive metrics are variable across time. These results show that because fitness results from a wide variety of ecological processes, accurate assessments of adaptive habitat selection require a complex perspective. In addition, I have contributed to our knowledge of how vegetation influences dickcissel settlement patterns, while showing that preferred vegetation components have little influence on fitness. Other mechanisms (e.g., site fidelity, conspecific attraction, food availability, predator abundance) may thus play a stronger role in facilitating adaptive habitat selection. At the same time, I found strong evidence that vegetation altered by human activity shapes dickcissel habitat quality, and my results suggest that controlling invasive tall fescue may improve dickcissel nest success.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Nelson, Scott Brent

Contributors dc:contributor

• Miller, James R.
• Schooley, Robert L.
• Fraterrigo, Jennifer M.
• Benson, Thomas J.

• Brown-headed cowbird
• Dickcissel
• Fitness
• Grassland bird
• Habitat preference
• Habitat quality
• Spatial scale
• Spiza americana
• Tall fescue
• Vegetation

Statement dc:rights

• Copyright 2019 Scott Nelson

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/104845

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/104845