SS4.05 Tribute to Thomas Frost
Date: Monday, June 10, 2002
Time: 4:00:00 PM
Location: Sidney
 
COVICHAP, Colorado State University, Fort Collins, CO, USA, alanc@cnr.colostate.edu
Crowl, T, A, Utah State University, Logan, UT, , facrowl@cc.usu.edu
 
IMPORTANCE OF SPECIES COMPENSATION AND DETRITAL PROCESSING IN INSULAR TROPICAL STREAM FOOD WEBS.
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Compared to streams in continental montane forests, tropical insular headwater streams generally have fewer native species. Although most freshwater fishes and aquatic insects have limited dispersal abilities, some species with marine-based life histories are well adapted to exploit insular streams. These species are widespread because their larvae drift in oceanic current to many different estuaries. Their post-larvae migrate upstream over steep terrain and climb high waterfalls. Food webs frequently contain native species of gobies, nertid snails, as well as diverse atyid and palaemonid shrimp. These species represent relatively few functional feeding groups that dominate the food webs in upper elevations of these insular headwaters. How do these food webs persist with relatively limited functional redundancy? Our stream studies on Caribbean and Pacific islands indicate that even these few species constitute complex food webs. Some species can switch to grazing and/or predation as they mature and as resource availability changes. Most species are detritivores and we suggest that some of these consumers form processing chains that facilitate their use of microbially conditioned leaf litter. Others appear to compensate for loss or reductions in species diversity by altering their densities in response to storm flows and droughts. Understanding these dynamic responses is essential for conserving native species in these highly variable and often threatened habitats.