Print PageUnderstanding how changes in local environments impact regional populations of ESA listed species is a primary objective in managing fresh water ecosystems. In turn, regional population assessments rely on accurate estimates of local productivity and survival rates, which are directly influenced by the quality of suitable habitats. Defining habitat quality is an important problem in reducing uncertainty because linear relationships between local system drivers and individual responses are uncommon, with each increase in a given factor resulting in non-linear feedbacks on the fitness of focal species. We approach this problem by answering how the range and variability in a reduced set of environmental factors (water velocity, temperature) affect our predictions of habitat suitability in terms of the survival estimates for focal species. The broader impacts and dynamics of this question are exemplified by our ability to predict optimal drift-feeding in salmonids. We approach our question by integrating local environmental factors with bioenergetic trade-offs in a game-theoretic framework using virtual salmonid species. We compare the energetic costs and benefits predicted by a set of bioenergetic equations using an individual-based model of Brownian foragers. Survival potential is predicted by per capita intake rates along a flow gradient, while environmental heterogeneity is imposed through variability in the flow-field. Model predictions are compared to data from the literature.
Results/Conclusions
Results show that Brownian foraging effectively predicts observed mean per capita capture rates under a broad array of flow conditions, while over-estimating capture success at high flows. However, differences in optimal intake rates between species occur below aerobic swimming thresholds (e.g., critical swimming speeds), which fall within moderate flow regimes. Variability in energetic costs across bioenergetic models increased exponentially with increasing flow velocity, yet both statistical and mechanistic models showed a high degree of correspondence within the bounds of species-specific critical swimming speeds.
In conclusion, Brownian motion coupled with mechanistic bioenergetic models can effectively predict per capita gains under a wide range of bounded flow conditions. Critical swimming speeds can provide an effective threshold to bound our predictive range and effectively reduce the uncertainty associated with predicting growth potential. As improving our ability to predict seasonal growth rates across habitats directly improves survival estimates, initial assessments may benefit from focusing efforts on a reduced set of environmental variables and instead gather biological input, such as benthic and suspended prey biomass.
