Abstract
Animals frequently undergo periods when they accumulate lipid reserves for subsequent energetically expensive activities, such as migration or breeding. During such periods, daily lipid-reserve dynamics (DLD) of sentinel species can quantify how landscape modifications affect function, health, and resilience of ecosystems. Aythya affinis (Eyton 1838; lesser scaup; diving duck) are macroinvertebrate predators; they migrate through an agriculturally dominated landscape in spring where they select wetlands with the greatest food density to refuel and accumulate lipid reserves for subsequent reproduction. We index DLD by measuring plasma-lipid metabolites of female scaup (n = 459) that were refueling at 75 spring migration stopover areas distributed across the upper Midwest, USA. We also indexed DLD for females (n = 44) refueling on a riverine site (Pool 19) south of our upper Midwest study area. We found that mean DLD estimates were significantly (P<0.05) less than zero in all ecophysiographic regions of the upper Midwest, and the greatest negative value was in the Iowa Prairie Pothole region (-31.6). Mean DLD was 16.8 at Pool 19 and was markedly greater than in any region of the upper Midwest. Our results indicate that females catabolized rather than stored lipid reserves throughout the upper Midwest. Moreover, levels of lipid catabolism are alarming, because scaup use the best quality wetlands available within a given stopover area. Accordingly, these results provide evidence of wetland ecosystem degradation across this large agricultural landscape and document affects that are carried-up through several trophic levels. Interestingly, storing of lipids by scaup at Pool 19 likely reflects similar ecosystem perturbations as observed in the upper Midwest because wetland drainage and agricultural runoff nutrifies the riverine habitat that scaup use at Pool 19. Finally, our results underscore how using this novel technique to monitor DLD, of a carefully selected sentinel species, can index ecosystem health at a landscape scale.
Highlights
Prairie Wetlands Large proportions of wetlands in Iowa, Minnesota, and NorthDakota have been drained or otherwise lost in the past 200 years [1]
We propose that daily lipid-reserve dynamics (DLD) of sentinel species, during periods that necessitate lipid accumulation, can quantify how landscape modifications affect function, health, and resilience of ecosystems
DLD of birds collected at Pool 19 might be influenced by nocturnal fasting or long migratory flights [30,31], our estimates of DLD at Pool 19 could be biased toward smaller values
Summary
Dakota have been drained or otherwise lost in the past 200 years [1] In this modified agricultural landscape, remaining wetlands typically are large, permanent, and subject to various perturbations (e.g., ditches, drainage tile, sedimentation, cultivation) that degrade wetland quality [2]. The degree of wetland drainage or perturbation varies throughout the upper Midwest; proportionally more wetlands have been drained, and the surrounding upland landscapes are more intensely farmed in Iowa and southern Minnesota than in North Dakota [1,3]. Factors influencing trophic structure and wetland quality have important implications for ecosystem services, conservation, and management of wetlands and surrounding upland landscapes in the upper Midwest, USA [3,7]. The extent that drainage and perturbation influences wetland ecosystem processes or functions has not been evaluated within the upper Midwest and represents a critical research need. We predict that the quality of current ecosystem processes or functions would vary among regions of the upper Midwest and be related to relative levels of perturbations
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