PARENT SESSION
Oral Session #56: Spatial Ecology: Pattern,movement,dispersal.
Presiding: G. Hartvigsen
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom West, Radisson.
Habitat availability and arrangement: Effects on animals that are largely passively transported.
Nelson, Karen*,1, Palmer, Margaret1, Silver, Pamela2, 1 Department of Biology, College Park, MD2 School of Science, Erie, PA
ABSTRACT- Many animals have little control over their dispersal, except the choice to initiate or not to initiate movement. These passively dispersed animals cannot search for habitat efficiently, but must rely on encountering it by chance. For such animals, it may be easier to find habitat if it is divided among several patches rather than aggregated into a single large patch. Here we investigate the relative importance of habitat availability (i.e., proportion of the landscape made up of suitable habitat) and habitat arrangement (in this case, aggregated vs. subdivided habitat patches) to survival and success in locating habitat for passively dispersed animals. Using a spatially explicit, individual-based model of dispersal for small stream invertebrates, we show that arrangement and its interactions with availability could account for as much as 36% of the variability in survival and 66% of the variability in success in finding habitat for these animals. However, sensitivity tests indicate that the importance of subdivision decreases rapidly as the frequency and distance of passive transport increase. In order to parameterize the model more fully, we measured the likelihood of passive displacement from good habitat vs. intentional leaving from poor habitat for a very common stream taxon, larval chironomids. Further simulations then showed that habitat subdivision may be reasonably expected to be advantageous in natural systems under the very low flow conditions which can exist there for a large part of the year. We suggest that habitat subdivision may likewise be advantageous for other passively dispersed biota if dispersal distances are short and dispersal can be actively initiated.
KEY WORDS: fragmentation effects, passive dispersal, drift, habitat arrangement