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Plant distributions can be limited by habitat-biased herbivory, but the proximate causes of such biases are rarely known. Distinguishing plant-centric from herbivore-centric mechanisms driving differential herbivory between habitats is difficult without experimental manipulation of both plants and herbivores. Here, we tested alternative hypotheses driving habitat-biased herbivory in bittercress (Cardamine cordifolia), which is more abundant under the shade of shrubs and trees (shade) than in nearby meadows (sun) where herbivory is intense from the specialist fly Scaptomyza nigrita. This system has served as a textbook example of habitat-biased herbivory driving a plant's distribution across an ecotone, but the proximate mechanisms underlying differential herbivory are still unclear. First, we found that higher S. nigrita herbivory in sun habitats contrasts sharply with their preference to attack plants from shade habitats in laboratory-choice experiments. Second, S. nigrita strongly preferred leaves in simulated sun over simulated shade habitats, regardless of plant source habitat. Thus, herbivore preference for brighter, warmer habitats overrides their preference for more palatable shade plants. This promotes the sun-biased herbivore pressure that drives the distribution of bittercress into shade habitats.
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The structure of the thermal landscape determined behavioural and physiological responses to simulated predation risk
Although predators can deter an animal from regulating its body temperature by basking or shuttling, this response to predation should depend on the spatial distribution of thermal resources. By simulating predation risk, we showed that movement, thermoregulation and corticosterone of male lizards Sceloporus jarrovi depended on the spatial distribution of shade. Simulated risk caused lizards to move less, thermoregulate worse and circulate more corticosterone than they did without risk. However, a patchier distribution of shade enabled lizards to move more, thermoregulate better and circulate less corticosterone when exposed to a simulated predator. In the absence of simulated risk, lizards in patchier environments moved less, thermoregulated better and circulated less corticosterone, indicating the distribution of shade also affected the energetic cost of thermoregulation. This study provides the first test of a spatial theory of thermoregulation under the perceived risk of predation.
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- Award ID(s):
- 1655499
- PAR ID:
- 10510334
- Publisher / Repository:
- British Ecological Society
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 37
- Issue:
- 11
- ISSN:
- 0269-8463
- Page Range / eLocation ID:
- 2826 to 2839
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/1365-2435.14429
