is broad interest in better understanding the importance of landscape
linkages among what were once thought to be isolated ecosystems. Some
of the most interesting questions relate to linkages between aquatic
and terrestrial ecosystems, within aquatic systems such as littoral
pelagic linkages, and among aquatic systems such as lakes and the
coastal ocean. Landscape location and arrangement, and their
interaction with ecosystem size, may have important impacts on the
strength linkages among ecosystems and food webs.
collaboration with researchers at the University of Wisconsin - Madison
and the US Fish & Wildlife, David Post has studied the role of
migratory waterfowl in moving nutrients across the landscape of central
New Mexico (Post et al. 1998, Kitchell et al. 1999).
Birds are highly mobile vectors for nutrients. We found that
over-wintering snow geese and sandhill cranes transport nutrients from
farm fields, where they feed, to their roosting sites in managed
wetlands at the Bosque del Apache National Wildlife Refuge. Nutrient
inputs into these wetlands both augment nutrient availability and
change nutrient cycling through modification of nitrogen-to-phosphorus
ratios (bird excretion has low N:P). Although loading was extremely
high in the few wetlands where the majority of geese roost (about half
of the total annual nutrient load for those wetlands), the impacts were
diluted at the larger spatial scale of the entire wetland complex where
bird born nutrient had little effect on ambient nutrient
concentrations. This project was especially germane in the Southwest
where water quantity and quality, and the use of water by humans and
wildlife, are in potential conflict. High nutrient inputs by birds
exacerbate conservation and management problems associated with high
bird densities and limited water supply.
Post has also worked to understand how food webs dynamics may be
influenced by the movement of predators or the flow of energy and
nutrients across ecosystem and sub-ecosystem boundaries. Using
theoretical models, David has addressed how food web linkages created
by mobile top predators may influence dynamical properties of food webs
(Post et al. 2000).
David has also addressed the problems with defining boundaries for of
ecosystem, and how our definition of an ecosystem boundary is
influenced by the questions we ask (Post et al. 2007).
Members of the Post lab have also explored the role of subsidies between systems of similar produtivity (Paetzold et al. 2008). Theoretical work suggest that the importance of allochthonous (subsudy) inputs depends upon the productivity gradient between adjacent system. Much of the previous work on allochthonous (subsudy) inputs have focused on systems where there is a strong gradient in resource production (e.g., desert islands, cobble bars along productive islands). There exists very little empirical evidence for the importance of allochthonous inputs in systems where productivity of the recipient habitat is relatively high and not overwhelmed by the productivity of the donor habitat. We have tested these ideas on Horse Island, in Long Island Sound. The forest of Horse Island is more productive then the relatively productive waters of Long Island Sound which surround the island. We used pitfall traps and stable isotope techniques to addressed the questions a) to what degree do major guilds of terrestrial arthropods derive energy from marine inputs, b) how far do marine resources penetrate the island, and c) whether arthropod consumers are more abundant near shore than in inland areas . Our results provide the first estimates of the importance of marine resources to a terrestrial system where net primary production in the recipient habitat is similar to that of the donor habitat (Paetzold et al. 2008).
Emerging work in the Post lab on anadromous and landlocked alewives adds a new element to our research on spatially linked food web interactions. In coastal lakes throughout New England, life history difference between landlocked and anadromous alewives mediate the spatial scale of interactions between alewife populations and local communities and ecosystems. Anadromous alewife populations create a spatial linkage between lakes where they spawn and the coastal ocean where they spend much of their life. In contrast, landlocked alewives provide no spatial linkage outside the lake in which they reside because dams or other similar impediments have severed their migratory route to the coastal ocean. Because alewives are important as both predators and prey, they provide a system for simultaneous consideration of the effects of mobile predators and prey subsidies. Anadromous alewives are important vectors for moving marine derived nutrients into freshwater ecosystems (Post and Walters in review; Walters et al. in review) and important prey for many coastal breading birds like cormorants (Dalton et al. in press) and osprey and for fish predators in many coastal lakes. Alewife lakes along the coast of New England provide a powerful context in which the Post Lab will address the question: how do spatial linkages driven by mobile organisms mediate local dynamics? Because differences in spatial linkages emerge from variation in life history strategies, alewives also provide a model system for addressing a secondary question: how do intraspecifc phenotypic differnces (a results of life history evolution) influence population, community and ecosystem dynamics?
Related publications (Publications):
A.W., and D.M. Post. In review. Anadromous alewives contribute
marine-derived nutrients to coastal stream food webs. Submitted to Canadian Journal of Fisheries and Aquatic Sciences.
Post, D.M. and A.W. Walters. In review. Nutrient excretion rates of
anadromous alewives during their spawning migration. Submitted to Transactions of the American Fishery Society.
Dalton, C.M., D. Ellis, D.M. Post. In review. The impact of Double-crested Cormorant predation on anadromous alewives in south-central Connecticut. Canadian Journal of Fisheries and Aquatic Sciences.
Paetzold, A., M. Lee, and D.M. Post. In press. Marine resource flows to terrestrial arthropod predators on a temperate island – the role of subsidies between systems of similar productivity. Oecologia.
Post, D.M., M.W. Doyle, J.L. Sabo, and J.C. Finlay. 2007. The problem of boundaries in defining ecosystems: a potential landmine for uniting geomorphology and ecology. Geomorphology 89:111-126.
Post, D.M., M.E. Conners, and D.S. Goldberg. 2000. Prey preference by a top predator and the stability of linked food chains. Ecology 81:8-14.
J.F., D.E. Schindler, B.R. Herwig, D.M. Post, M.H. Olson, and M.
Oldham. 1999. Nutrient cycling at the landscape scale: the role of diel
foraging migrations by geese at the Bosque del Apache National Wildlife
Refuge, New Mexico. Limnology and Oceanography 44:828-836.
D.M., J.P. Taylor, J.F. Kitchell, M.H. Olson, D.E. Schindler, and B.R.
Herwig. 1998. The role of migratory waterfowl as nutrient vectors in
managed wetlands. Conservation Biology 12:910-920.