e-journal

Does dispersal control population densities in advection-dominated systems? A fresh look at critical assumptions and a direct test

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Summary
1. In advection-dominated systems (both freshwater and marine), population dynamics are usually
presumed to be dominated by the effects of migrants dispersing by advection, especially over
the small spatial scales at which populations can be studied, but few studies have tested this presumption.
We tested the hypothesis that benthic densities are controlled by densities of dispersers
for two aquatic insects in upland streams.
2. Our study animals were two species of caddisflies (Hydropsychidae), which become sedentary
filter-feeders following settlement onto substrata. Densities of dispersers in the drift
(advective dispersal) were quantified using nets placed along the upstream edges of riffles,
where the latter abruptly abutted a slower, upstream run. Settlement was estimated at each
site using brick pavers, half of which had been fenced to prevent colonization of their top surfaces
by walking hydropsychids, thus allowing us to distinguish also the mode of movement
during settlement.
3. First through fifth instars of two species, Smicrophylax sp. AV2 and Asmicridea sp. AV1, were
abundant and showed disparate results. Drift and settlement were relatively strongly related for
Smicrophylax. The best fit lines were shown by second and third instars settling on plain bricks,
suggesting that drift played a strong role in settlement, but that some drifters dropped to the bottom
and located substrata by walking. Quantile regression suggested that drift sets limits to settlement
in this species and that settlement success was highly variable. In contrast, settlement by
Asmicridea was poorly related to drift; settlers were mainly individuals re-dispersing within sites.
4. Smicrophylax densities appear to be controlled by dispersal from upstream, but benthic density
of Asmicridea is more likely linked to local demography. Our data demonstrate the dangers of
assuming that supposedly drift-prone species can all be modelled in the same way. Alternative
models emphasizing little or different kinds of movement should be considered. Variability in oviposition
coupled with weak dispersal, for example, is a viable alternative hypothesis to explain variation
in benthic density along channels. Moreover, the constraints on settlement of Smicrophylax
show that immigrants into sites can be in short supply, an hypothesis rarely considered in stream
research.

Key-words: Australia, caddisflies, flow, streams, Trichoptera

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Ketersediaan

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Informasi Detail

Judul Seri

Journal of Animal Ecology

No. Panggil

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Penerbit

London : British Ecological Society., 2010

Deskripsi Fisik

Journal of Animal Ecology 2010, 79, 235–248

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

BIOLOGI

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

Versi lain/terkait

Lampiran Berkas

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