Populations and communities
Dispersal, recruitment and population dynamics of animals with complex life-cycles
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The influence of dispersal stages on the population dynamics of organisms with complex life cycles is poorly understood. We tested whether the larval abundance of a stream caddisfly was limited by the availability and dispersal of adults. Late-instar larval Zelandopsyche ingens (Fig. 1), found only in Nothofagus beech forest streams, were removed from 200 m reaches of three small streams, halving the potential local production of adults. The larvae removed were added to three other streams, doubling potential local production of adults. Egg mass abundances (Fig. 2) were subsequently measured at these and three control streams to determine whether Z. ingens abundance depended on the local production of adults or the connection of subpopulations by dispersing adults.The number of egg masses was unrelated to the manipulated larval number. All streams received enough eggs to replace the previous larval population, but patterns of larval survivorship varied considerably depending on the number of eggs received by a stream. The local abundance of leaf litter resources (the primary food of the caddis) appeared to have the biggest influence on this process. Survivorship was very high in streams with low recruitment and abundant resources, and massive mortality occurred in streams with large number of recruits, but few resources. Thus, processes affecting both adult and larval populations influenced population dynamics, but the abundance of late-instar larvae was primarily determined by conditions within the larval habitat. |
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Figure 1. Late-instar Zelandopsyche ingens larva. |
Figure 2. Egg mass of Zelandopsyche ingens. |
People involved in this project
University of Canterbury
Angus McIntosh
Hamish Greig
Publications
Greig & McIntosh 2008. Density reductions by predatory trout increase adult size and fecundity of surviving caddisfly larvae in a detritus-based stream food web. Freshwater Biology 53: 1579-1591 (pdf, 220kb).