Physiological adaptation to ecological heterogeneity

I am interested in behavioral and physiological adaptations that enable animals to maintain positive energy balance when foraging opportunities are patchy in time. This work falls into three categories:

1. Excess capacity

Why do football stadiums have so many toilets? It’s not because of how much beer the

fans drink, but instead the pulsed nature of their bathroom visits–the halftime stampede.

In shaping the physiological capacity of organisms, natural selection demonstrates similar design considerations, causing traits to exhibit excess capacity if demands vary in time. Daniel Schindler and I reviewed estimates of digestive capacity in predatory fishes and found that they typically have the guts to consume 2-3-times the amount of food that they regularly encounter. This much excess capacity suggests predator-prey encounters are far patchier than assumed in biology and that binge-feeding enables predators to survive despite regular periods of famine.

Armstrong, J.B, and D.E. Schindler. 2011. Excess digestive capacity in predators reflects a life of feast and famine. Nature. 476: 84-87 Science Magazine

2. The physiological underpinnings of dine and dash foraging strategies 

I’m interested in how physiological capacities along the food-to-fuel pathway (e.g. the steps spanning foraging and assimilation) support behavioral strategies that involve eating in one place and processing food in a different place (e.g. habitat cycling). Specifically, I study how the ratio of foraging: digestive capacity in coho salmon affects the energetic profitability of diel movement behavior. The high stomach capacity of juvenile coho salmon allows them to consume huge amounts of food in short periods of time; individuals could consume nearly 1/5 of their body mass in salmon eggs during a 15-min. feeding trial (see photo below). However, these fish required ~3 days to process this huge, lipid-rich meal. This represents an extreme level of excess foraging capacity–fish foraged at rates >100-times faster than what their digestive systems could keep pace with. Why invest in a large stomach if it only exacerbates digestive bottlenecks? The coho salmon that I study forage for salmon eggs in cool habitat and move to warmer habitat to digest their meals. Stomach capacity determines how many salmon eggs individuals can acquire during each feeding foray. Larger stomachs require fewer feeding forays to reach a given level of energy intake. Thus, the seemingly excessive stomachs of coho salmon likely reduce the energetic costs and predation risk incurred during their foraging movements. This suggests that large stomachs may be a key feature to foraging strategies that exploit spatial heterogeneity in the environment.

Armstrong, J.B., D.E Schindler, C.P. Ruff, G.T. Brooks, and C.E. Torgersen. 2013. Diel horizontal migration in streams: juvenile fish exploit spatial heterogeneity in thermal and trophic resources. Ecology 94: 2066–2075

3. Phenotype flexibility

Research in birds and snakes reveals that individuals can rapidly and reversibly manipulate organ size to match their physiological capacites to ambient ecological conditions. Morgan Bond and I found that Dolly Varden manipulate organ size to survive extreme, but predictable seasonal variation in foraging opportunities. This represents one of the first demonstrations of phenotype flexibility in wild fish.

http://seattletimes.com/html/localnews/2020605591_fishgutsxml.html

Armstrong, J.B. and M.H. Bond. Phenotype flexibility in wild fish: Dolly Varden regulate assimilative capacity to capitalize on annual pulsed subsidies. In press: Journal of Animal Ecology