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The predator-permanence hypothesis predicts that as hydroperiod increases in lentic ecosystems, biotic interactions—mainly predation—replace physical factors like drying as the main determinant of community structure and population dynamics. We propose that the same transition occurs over time in seasonally flooded ecosystems that are connected to permanent water bodies. To test for evidence of successional changes that are similar to spatial changes in the relative importance of drying and predation, we used a 12-y time series of snail density, predator density, and water depth at 4 sites arranged along a nutrient gradient in a subtropical, seasonally flooded wetland, the Florida Everglades, USA. The rate of change in snail population size was negatively correlated with their density at all 4 sites, suggesting that density-dependent factors such as resource limitation regulate snail dynamics. The strength of the relationship varied among sites such that when water depth changes were less important, snail population size was more important in predicting changes in snail population size. At the site that consistently had the greatest snail density, crayfish density negatively affected the rate of snail population change, suggesting that crayfish predation may limit snail population growth in areas with more or higher-quality resources that support larger snail populations. Tethering studies were also conducted, which revealed higher snail mortality in the wet season, primarily because crushing predators (e.g., molluscivorous fishes) were more common at that time and added to the chronic mortality by entry-based predators (e.g., crayfish, which access snails through their aperture). In summary, 3 of the sites resembled temporary or permanent fishless ponds where snail populations were primarily structured by abiotic factors, intraspecific competition, and invertebrate predators (e.g., crayfish) during the wet season, whereas 1 site showed evidence that snail populations were also influenced by molluscivorous fish. This temporal change in importance of water permanence factors to fish that affected population dynamics supports the spatial pattern proposed by the predator-permanence hypothesis.
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This content will become publicly available on November 1, 2026
Widespread Heterogeneity in Density‐Dependent Mortality of Nearshore Fishes
ABSTRACT Debates over whether and how populations are regulated have recently shifted away from detecting and instead towards quantifying the strength of density dependence and its variation among systems. Yet, the degree of variation in density‐dependent mortality and the factors driving this variation remain poorly understood. Here, we conducted a meta‐analysis of 38 reef fish species across 56 studies, which yielded 147 estimates of intraspecific density‐dependent mortality, primarily during early or small life stages. The magnitude of density‐dependent mortality (the increase in the per capita mortality rate due to one fish per unit area of habitat) was surprisingly inconsistent both within and among species. Several factors emerged as drivers of variation. Predators amplified the negative effects of density, and density‐dependent mortality was greater for species that typically colonize at low densities or achieve larger maximum sizes. However, even within a single species, the strength of density‐dependent mortality varied dramatically—often by several orders of magnitude—and sometimes changed sign. This heterogeneity likely reflects multiple processes acting together, including environmental context (e.g., predator density or refuge availability), traits of the focal organism (e.g., size) and methodological differences (e.g., study design) among studies. Our results underscore the need for future efforts to quantify and report ancillary variables and strive to identify how much these factors contribute to population regulation.
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- Award ID(s):
- 1851032
- PAR ID:
- 10654528
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 28
- Issue:
- 11
- ISSN:
- 1461-023X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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