PARENT SESSION
Oral Session # 82: Aquatic Ecology: Freshwater.
Presiding: A Soja
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.
Linking landscape patterns of resource distribution with models of aggregation in ovipositing caddisflies.
Lancaster, Jill1, Downes, Barbara*,2, Reich, Paul2, 1 University of Edinburgh, Edinburgh, Scotland, Scotland2 University of Melbourne, Melbourne, Australia, Australia
ABSTRACT- Spatially-explicit measures of dispersion were employed to detect how any aggregation of individuals is influenced by the dispersion of resource patches. For two species of caddisfly (Hydrobiosidae) in two stream stretches, we mapped the spatial distribution of potential and exploited patches (emergent rocks as oviposition sites), and enumerated egg masses. As documented previously, egg masses of Ulmerochorema and Apsilochorema were aggregated on individual rocks and both species showed velocity-specific preferences for oviposition sites: oviposition sites of Ulmerochorema occurred most often in fast flowing water; those of Apsilochorema in slow water. Point pattern analysis was used to describe the spatial pattern of emergent rocks, and to test hypotheses about how site selection behaviour of females influences dispersion. Emergent rocks were clumped and equally abundant in both stretches. Our perception of how caddisflies deposit eggs into the landscape varied with the neutral landscape model. The most informative NLM compared the spatial pattern of oviposition sites with the underlying pattern of emergent rocks, while constraining the random selection of rocks to reflect species' velocity preferences. Oviposition sites of Ulmerochorema were clumped spatially, over and above the background pattern; those of Apsilochorema were over-dispersed spatially.
Key words: dispersion, patches, streams