PARENT SESSION
Oral Session #11: Aquatic Ecology: Conservation, Plankton, Invertebrates.
Presiding: C. Cooper
Monday, August 5. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.
Stream insect populations connected through cross-stream and upstream adult flight.
MACNEALE, KATE*,1,2, PECKARSKY, BARBARA1, LIKENS, GENE2, 1 Cornell University, Ithaca, NY2 Institute of Ecosystem Studies, Millbrook, NY
ABSTRACT- Populations across habitats can be connected depending on the distribution and connectivity of available habitat and the organism's dispersal behavior. We used an isotopic tracer, 15N, to label stoneflies (Leuctra ferruginea) in a mass mark–recapture experiment to determine the distances and pathways of adult flight within and among streams. We added 15N–NH4Cl continuously for eight weeks in summer 2000 to Zig Zag Brook, a first order stream within Hubbard Brook Experimental Forest, NH. All stoneflies emerging from a ∼370m section downstream of the addition were labeled. We collected flying stoneflies using sticky traps placed every 50 m 1) for 600 m upstream and downstream of the labeled section of Zig Zag, 2) along an adjacent stream that flows into Zig Zag 350 m below the labeled section, and 3) along a 550–m forested transect between the labeled section of Zig Zag and the adjacent stream. Of labeled individuals captured, 85% flew upstream along Zig Zag, with the average female flying upstream ∼239 m (± 19 m) and the farthest flying ∼885 m. These data corroborate results from three similar studies we have done. We observed cross–stream colonization as 15 of 205 individuals analyzed from the adjacent stream were labeled. Few individuals were caught on the cross–watershed transect, but of 96, three were labeled, including one in the middle of the transect and two within 50 m of the adjacent stream. The stream channel appears to be a corridor for flight but primarily in the upstream direction, and the forest is not a barrier to flight across watersheds. Because these individuals drift little as larvae and fly predominantly upstream, populations from headwater streams may exchange more individuals with populations from nearby streams that are separated only by mountain ridges than with distant populations that are within the same valley.
KEY WORDS: dispersal, habitat connectivity, Hubbard Brook Experimental Forest, stable isotopes