Abstract
Interactions between predators and their prey are influenced by the habitat they occupy. Using created oyster (Crassostrea virginica) reef mesocosms, we conducted a series of laboratory experiments that created structure and manipulated complexity as well as prey density and “predator-free space” to examine the relationship between structural complexity and prey survivorship. Specifically, volume and spatial arrangement of oysters as well as prey density were manipulated, and the survivorship of prey (grass shrimp, Palaemonetes pugio) in the presence of a predator (wild red drum, Sciaenops ocellatus) was quantified. We found that the presence of structure increased prey survivorship, and that increasing complexity of this structure further increased survivorship, but only to a point. This agrees with the theory that structural complexity may influence predator-prey dynamics, but that a threshold exists with diminishing returns. These results held true even when prey density was scaled to structural complexity, or the amount of “predator-free space” was manipulated within our created reef mesocosms. The presence of structure and its complexity (oyster shell volume) were more important in facilitating prey survivorship than perceived refugia or density-dependent prey effects. A more accurate indicator of refugia might require “predator-free space” measures that also account for the available area within the structure itself (i.e., volume) and not just on the surface of a structure. Creating experiments that better mimic natural conditions and test a wider range of “predator-free space” are suggested to better understand the role of structural complexity in oyster reefs and other complex habitats.
Highlights
Structural complexity is the physical arrangement of objects in space [1], and is a fundamental property of all ecological systems
We examined the relationship between prey survivorship and habitat structure and its complexity, and whether these interactions are influenced by prey density or the amount of ‘predator-free space’
Prey survivorship was significantly lower in the control (4.5%) treatment than the low treatment (71.5%; p,0.001), and survivorship in both control and low were significantly lower than the intermediate treatment (84.5%; p = 0.01) (Fig. 1)
Summary
Structural complexity is the physical arrangement of objects in space [1], and is a fundamental property of all ecological systems. By varying the availability and type of microhabitats available, structural complexity may influence predator-prey interactions and have significant impacts on the local faunal community (e.g., [2,3,4,5,6]). By decreasing the visibility of predators or obstructing prey movement, structural complexity may negatively impact prey survivorship [11,12,13]. Understanding the potential effects of habitat structure and its complexity on prey survivorship is becoming increasingly important as anthropogenic and climateinduced stressors are significantly changing the physical and ecological structure of many ecosystems
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