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Abstract Many critical drivers of ecological systems exhibit regular scaling relationships, yet the underlying mechanisms explaining these relationships are often unknown. Trophic interaction strengths, which underpin ecosystem stability and dynamics, are no exception, exhibiting statistical scaling relationships with predator and prey traits that lack causal, evolutionary explanations. Here we propose two universal rules to explain the scaling of trophic interaction strengths through the relationship between a predator’s feeding rate and its prey’s density --- the so-called predator functional response. First, functional responses must allow predators to meet their energetic demands when prey are rare. Second, functional responses should approach their maxima near the highest prey densities that predators experience. We show that independently parameterized mathematical equations derived from these two rules predict functional response parameters across over 2,100 functional response experiments. The rules further predict consistent patterns of feeding rate saturation among predators, a slow-fast continuum among functional response parameters, and the allometric scaling of those parameters. The two rules thereby offer a potential ultimate explanation for the determinants of trophic interaction strengths and their scaling, revealing the importance of ecologically realized constraints to the complex, adaptive nature of functional response evolution.
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Predator feeding rates may often be unsaturated under typical prey densities
Abstract Predator feeding rates (described by their functional response) must saturate at high prey densities. Although thousands of manipulative functional response experiments show feeding rate saturation at high densities under controlled conditions, it remains unclearhowsaturated feeding rates are at natural prey densities. The general degree of feeding rate saturation has important implications for the processes determining feeding rates and how they respond to changes in prey density. To address this, we linked two databases—one of functional response parameters and one on mass–abundance scaling—through prey mass to calculate a feeding rate saturation index. We find that: (1) feeding rates may commonly be unsaturated and (2) the degree of saturation varies with predator and prey taxonomic identities and body sizes, habitat, interaction dimension and temperature. These results reshape our conceptualisation of predator–prey interactions in nature and suggest new research on the ecological and evolutionary implications of unsaturated feeding rates.
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- Award ID(s):
- 2129758
- PAR ID:
- 10578131
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 26
- Issue:
- 2
- ISSN:
- 1461-023X
- Page Range / eLocation ID:
- 302 to 312
- 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/ele.14151
