摘要:

SUMMARY1. Temporal changes in species richness, total abundance, and numbers of individuals in seven functional feeding groups were compared between pools and riffles at four sites on two intermittent streams in Victoria sampled during a drought year followed by a wetter year.2. Species richness increased steadily over time, peaking in the riffles just before flow ceased. Maximum species richness occurred in the pools shortly after flow stopped, implying emigration from the drying riffles. There were two peaks in total numbers, first in autumn when flow commenced and again in late summer as flow diminished. Generalist feeders (collector‐gatherers and collector‐scrapers) were usually abundant throughout the year. Scraper densities rose in late spring‐early summer in conjunction with enhanced periphyton growth, whereas predator numbers steadily increased during the year, peaking in all habitats just before they dried.3. Several floods in spring significantly reduced species richness and total numbers of individuals but recovery to pre‐flood levels was generally complete within 2 weeks. Although floods had little effect upon succession, as indicated by trajectories in ordination space, the dry period interrupted otherwise cyclical sequences, consistently resulting in arch‐shaped trajectories. Faunal change appeared to be allogenic, driven by the seasonal cycle of environmental phases.4. A group of early colonists or ‘pioneer’ species was replaced after several weeks by heterogeneous groups of ‘mid‐successional’ taxa responsible for differences in faunal composition between riffles and pools. When flow diminished, these groups were replaced by ‘summer’ species, apparently capable of tolerating deteriorating environmental conditions, and potentially intensifying biotic interactions.5. We suggest that the cyclical temporal changes in assemblage composition observed in this study represent ‘seasonal periodicity’, whereas recovery after unpredictable disturbances such as floods that temporarily disrupt the cycle fits the definition of ‘succession’. Succession rate is a measure of resilience, recovering to the cyclical trajectory that would exist in the absence of disturbance. ‘Lag effects’ brought about by reduced recruitment during the drought were not evident until the following year, emphasizing the significance of historical events and the need for long‐term studies to describe the ecolo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00528.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Larvae ofSimulium noelleriformed dense aggregations (>60 larvae cm−2) at a lake outlet where water passed in a very thin film vertically over wooden planks. Despite the high densities there was sufficient space between larvae to allow water to flow within an aggregation as well as over its surface.2. Small larvae, occluded within an aggregation, had a faster midgut throughput rate than larger larvae. Both had rates that were similar to those recorded in the literature for a range of habitats and species. The same relationship of throughput rate and larval size was maintained from upstream to downstream across 20cm of an aggregation.3. Material passed through the midgut of larvae of a given size at a constant rate, indicating that assimilation efficiency of the whole gut contents was low.4. By colour‐banding larval gut contents with fluorescent dye it was possible to demonstrate that faecal pellets are a component of the larval diet in the dense aggregations, especially of small larvae.5. The abundance of four easily identifiable components of the lake seston were measured from water samples above, and below, a larval aggregation. Particles with a mean diameter of 40 μm, or greater, showed significant reductions in numbers over a stream length of 6cm. Particles of smaller size showed reductions but these were not signifi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00529.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY