Сезонная динамика сообществ

Сезонная динамика сообществ

Пространственная и сезонная структура макробентоса

BIOLOGY AND ENVIRONMENT-PROCEEDINGS OF THE ROYAL IRISH ACADEMY 1993, Vol 93B, Iss 3, pp 115-126

Abstract:

Between-site differences and within-site seasonal patterns were studied in benthic macroinvertebrate communities from two physically and chemically contrasting streams in the River Blackwater catchment (the River Awbeg and the Glenfinnish River). Between-site differences occurred in species composition (related to water hardness, pH and stream order), total macroinvertebrate densities (related to hardness and riparian vegetation), diversity and functional group organisation (partially related to water chemistry, but also to riparian vegetation and stream order and distance from headwaters). Total density, taxon richness, numbers of shredders, filterers and deposit collectors and relative abundance of filterers were greatest in the higher-order, hard-water Awbeg. Diversity and relative abundance of grazers and predators were greatest in the lower-order, softer-water Glenfinnish.

Seasonal changes in total invertebrate numbers, diversity, rank/abundance distributions and functional group organisation were also observed. Overall densities were greatest in late summer/early autumn and lowest in early summer in the Glenfinnish River. Seasonality patterns in invertebrate abundance in the Awbeg were dominated by Simuliidae. peaking in late summer. Rank abundance distributions varied from log series to geometric patterns over the year. Taxon richness and abundance of shredders and filterers increased in late summer in both rivers in accord with seasonal patterns predicted under the River Continuum Concept. Other seasonal patterns, e.g. in grazers, did not; this was related to the local habitat conditions (e.g. shading).

Водотоки: сезонная динамика бентоса.

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

John F. Murphy and Paul S. Giller

Summary

2. Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.

3. Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.

4. Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.

5. Within-stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between-stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

Водотоки: сезонная динамика бентоса. Непал.

Volume 44 Issue 4 Page 581 - August 2000

The seasonal dynamics and persistence of stream macroinvertebrates

in Nepal: do monsoon floods represent disturbance?

P.A. Brewin S.T. Buckton S.J. Ormerod

1.The monsoon causes major flood events in some Himalayan streams, but their

seasonal predictability might reduce the resulting disturbance. We assessed

seasonal change in the benthos of 16 streams in central Nepal over a gradient of

declining rainfall and increasing altitude from 600 to 3800 m. All sites were surveyed

on four occasions, two in winter (November) and two pre-monsoon (June), with

additional sampling during the monsoon (August) at four low altitude sites.

Invertebrate abundance, taxon richness and persistence were assessed at all sites,

and density and meso-habitat distribution at the four low altitude sites only.

2.Strong seasonal variation among invertebrates was confined primarily to streams

at low altitude (600-800 m) where monsoon rainfall was greatest and catchments

were dominated by terraced agriculture. At these sites, a significant reduction in

benthic density (on average by 77%) and taxon richness (by 20%) occurred

between the winter and pre-monsoon periods, so that invertebrate numbers were

already low before the monsoon. A further significant decline occurred in all meso-

habitats during the monsoon, but the change in density was small in absolute terms.

3.Persistence in rank abundance was equally low at all sites, but turnover in

composition was significantly lower at sites in semi-natural forest than in

catchments managed for terracing or alpine pasture.

4.These data provide no evidence that monsoonal floods represent major

disturbance, instead supporting the view that the ecological response might reflect

an adjustment to predictable flow pattern. However, catchment land use in the

Himalaya appears to be a significant source of ecosystem instability, and confounds

the simple interpretation of monsoon effects.