10 The context of habitat complexity: The role of temporal constraints in mediating predator-prey dynamics in intertidal structured and unstructured habitats

Friday, August 7, 2009: 11:10 AM
Blrm B, Albuquerque Convention Center
Kirstin K. Holsman , Fisheries Ecology, Northwest Fisheries Science Center, NOAA Fisheries Service, Seattle, WA
P. Sean McDonald , Fisheries, Univeristy of Washington School of Aquatic and Fishery Sciences, Seattle, WA

Many studies have explored the role of habitat complexity in mitigating species interactions with the general consensus that structured habitats increase species diversity and abundance through higher niche diversity, attenuation of resource competition, and modulation of predator/prey interactions. Unstructured intertidal habitats are also undoubtedly important to a variety of species, yet the role of these areas in supporting migratory aquatic predators is frequently overlooked in ecological investigations and absent from subsequent conservation efforts predicated on ecological valuations of habitats. In part the scarcity of information regarding use of unstructured areas by migratory predators arises from a lack of a mechanistic understanding of the effect of limited foraging time and intertidal structure on predator movements during tidal inundation. Predators foraging under temporal constraints must weigh the cost of resource acquisition (i.e., search and handling time) and mortality risk (e.g. stranding) with energetic return. Under temporal constraints, decisions regarding habitat use are modified by an ultimate temporal limit to search and handling time that varies with distance from a central place (i.e., subtidal channel). Valuable predictions regarding intertidal predator/prey dynamics can be derived by combining the principles of central place foraging theory with models of predator/prey interactions in complex habitats.


In this talk we will present: (1) a theoretical model for incorporating temporal constraints in classical predator and prey models; (2) results of laboratory experiments and model simulations that estimate the main and interacting effects of temporal constraints on consumption rates in unstructured and structured areas; and (3) validation and parameterization of the theoretical model, including broader applications to various systems and species. Specifically, the theoretical model predicts a decoupling of predator and prey populations in intertidal areas that increases across tidal and habitat complexity gradients. Experimental and simulation results using predatory crabs (Cancer spp.) corroborate the model and show that temporal constraints on foraging mediate predator/prey populations in unstructured intertidal habitats in a way analogous to physical structure in subtidal areas. Our results resolve persistent questions regarding subtidal predator and intertidal prey populations such as oft reported type II and type III functional responses in unstructured habitats and cross-boundary spatial subsidies of subtidal predators. Since unstructured intertidal areas remain largely unprotected, the conservation implications of our results are important in terms of increasing alteration and fragmentation of unstructured habitats by a variety of human activities and related processes (e.g., dredging, aquaculture, and invasive species expansion).

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