Differences In Assemblage Composition Research Articles

COMPARATIVE ECOLOGY OF NORTH ATLANTIC SHORES: DO DIFFERENCES IN PLAYERS MATTER FOR PROCESS?

The contrasting histories of the western and eastern shores of the North Atlantic Ocean provide an excellent opportunity to consider the implications of past events for present ecological processes and the functioning of marine ecosystems. Similarities and differences in assemblage composition have been driven by large-scale events, such as the trans-Arctic interchange, which has shaped the species pool, and cycles of glaciation, which have determined phases of local or regional extinction and colonization. More recently, anthropogenically induced invasions and local extinctions have significantly altered biogeographic distributions. Here we consider for both hard and soft substrata how the presence or absence of key taxa influences the outcomes of trophic and other biological interactions, and evaluate the consequences for community structure and ecosystem functioning. On intertidal hard substratum shores, biodiversity of epilithic microphagous grazers differs across latitudinal and longitudinal scales. Diversity is high in southern Europe but declines to the north and across the Atlantic. Lower diversity and the absence of patellid limpets in Iceland and the northwest Atlantic compared to Europe result in differences in consumer pressure, and an apparent contrast in the importance of herbivory vs. competitive interactions and predation pressure as community structuring processes. Interestingly, despite differences in "process," community patterns are remarkably similar between the east and west. On soft sediment shores, there are conspicuous geographic differences in importance of bioturbators and large digging predators. Hemichordates can be abundant and important infaunal bioturbators in the western Atlantic, but they generally play a much reduced role in the eastern Atlantic. In addition, the number and diversity of digging predators on western Atlantic shores is high; the horseshoe crab, swimming portunid crabs, large whelks, excavating waterfowl, and an abundance of skates and rays exert intense predation pressure and associated biogenic disturbance to sediments. In Europe, except for excavating waterfowl these taxa are rare or absent. Thus, the importance of large, biological agents of disturbance is lower on European shores as a consequence of both recent anthropogenic pressure and natural processes over larger time scales. Consideration of key structuring taxa over the Atlantic shows that human-mediated transport has had considerable influence. Faunas on both sides of the Atlantic are becoming more similar to the point that some of the key differences in assemblage composition and hence community organization have blurred. Recent introductions as well as planned experimental manipulations provide the opportunity to understand the role of species identity in determining community structure and ecosystem functioning over large spatial scales; the North Atlantic may be an ideal test system to explore these areas.

Assemblage Formation as a Result of Raw Material Acquisition in Western New South Wales, Australia

Quarries are often defined as locations where people in the post gained access to raw material. Here we consider the definition of quarries in a raw material-rich environment. Stone artifacts found adjacent to two silcrete outcrops that might be labeled as “quarries” are compared with those found at a creek-side “occupation “location in western New South Wales, Australia. We investigate these attributions by considering the technology of raw material procurement in relation to the chronology implied by the age of the surfaces on which the artifacts rest. We assess assemblage patterning in relation to the time period over which assemblages were deposited at each of the locations. Time provides a more useful means than function for understanding differences in assemblage composition.

Small mammal assemblages and habitat distribution in the northern Junggar Basin, Xinjiang, China: a pilot survey

Small mammal assemblages were surveyed in five areas of the northern Junggar basin, Xinjiang, China, using standard trapping methods and index transects. 23 species were recorded. The relationships between habitats and the distribution of the main species were described at local scale in Baihaba, Altai mountains. Three types of assemblages were identified linked to (i) forest (Myodes rufocanus, Microtus agrestis, Myodes rutilus, Apodemus peninsulae, Sorex isodon), (ii) transitional areas and farmland (mixed pool of species including Apodemus uralensis), (iii) grassland (Ellobius tancrei, Microtus obscurus, Cricetulus migratorius). Additional species such as Microtus oeconomus could be found along small streams. At broader scale species composition was estimated in Kokehada, Nahenhobuke and Fuhai areas and compared. Although ecological gradients from mountain grasslands to cold semi-desert partly explain differences in assemblage composition on a regional scale, similar habitats at the same altitude may however harbour different assemblages. For example, Spermophilus erythrogenys was the dominant species of the Kokehada grassland and Microtus obscurus and Ellobius tancrei were dominant in Baihaba grassland. In conclusion, the need for multi-scale standard descriptions of small mammal assemblage distribution in the northern Junggar basin of China is pointed out

Detecting the effects of environmental change above the species level with beetles in a fragmented tropical rainforest landscape

Abstract 1. Invertebrate data identified to coarse groupings according to taxonomy or ecology are easier to obtain than species‐level data. However, it is unclear if such data are suitable for detecting environmental change.2. We compared the performance of four types of data (species, family, trophic group, and body size) to quantify the responses of beetle assemblages with three types of environmental change on the Atherton Tableland in north‐eastern Queensland, Australia. Clearing of rainforest creates two levels of environmental change: first the extreme, forest loss, and second, the more subtle change associated with forest fragmentation. A strong rainfall gradient across the study landscape also influences the biota, imposing a third type of environmental change, independent of rainforest modification.3. Almost 20 000 beetles were sampled from six replicate sites in each of pasture, small rainforest remnants, and both the edges and interiors of large rainforest remnants.4. All four types of data showed significant multivariate differences in assemblage composition between pasture and rainforest sites. Species‐level data in multivariate analyses showed an effect of fragmentation on small remnants and also showed variation which corresponded with the spatial aridity gradient across sites. Both of these patterns were only weakly evident or were non‐existent at the level of family, trophic group, or body size class. No level of taxonomic resolution gave consistently stronger results when univariate tests were applied to individual component taxa.5. We conclude that data above the species level may not have the sensitivity required to detect more subtle forms of environmental change.

Interactions between seagrasses and burrowing ghost shrimps and their influence on infaunal assemblages

The current study examined the direct interactions between intertidal seagrasses (Zosteraceae) and burrowing ghost shrimps (Callianassidae) and their influence on associated infaunal assemblages. Reciprocal transplant experiments conducted in two temperate regions revealed different interactions between both types of organism. In the U.S.A., seagrass prospered in all treatments, irrespective of the presence of ghost shrimp, whilst ghost shrimp declined in plots containing seagrass. In New Zealand, neither transplanted ghost shrimp nor seagrass became established in experimental plots, at the same time, neither type of organism appeared to be affected by the experimental addition of transplants. The differences in interactions between seagrass and ghost shrimp appeared to be related to seasonal differences in the timing of the transplant experiments and the pairing of particular ghost shrimp and seagrass species in each region. Infaunal assemblages showed distinct differences between seagrass and ghost shrimp treatments and reflected the dominant type of organism present. In treatments where transplanted seagrass or ghost shrimp became established, assemblage composition shifted in accordance with the type of transplanted organism. Differences in assemblage composition were characterised by higher relative abundances of discriminating taxa in treatments dominated by seagrass. The overall patterns of infaunal assemblage composition were correlated with a number of variables including the number of shoots, above-, below-ground seagrass biomass, % fines/sand, % total organic carbon, and sediment chlorophyll a. Findings from this study highlight the functional importance of intertidal seagrasses and burrowing ghost shrimps and reveal some of the ecological repercussions associated with changes in the distribution of these sympatric ecosystem engineers.

Habitat type influences fire resilience of ant assemblages in the semi-arid tropics of Northern Australia

Although fire is an annual occurrence in savanna systems and is widely used as a tool in conservation management, the effects of fire on biodiversity remain poorly understood. This study investigated the response of ant assemblages, a key component of invertebrate diversity, to burning in two dominant savanna ecosystems (spinifex uplands and sandplain) in the Australian semi-arid tropics. A total of 180 pitfall traps were established in each habitat and each sampling period (wet and dry season). We collected a total of 89 046 ants from 18 genera, representing 126 species. The response of ant assemblages to fire varied with habitat type. We relate this response to habitat-specific fire induced differences in microhabitat structure and the vertical distribution of biomass. There were large differences in assemblage composition in the spinifex habitat, where vegetation composition and structure varied considerably between burnt and unburnt sites. In contrast, assemblages were largely resilient to single fire events in the sandplain, where vegetation change following fire was less pronounced. This study highlights the need for conservation managers to be aware of how different habitats respond to fire and what the consequences of different management actions might be.

Small-scale diversity of Harpacticoida (Crustacea, Copepoda) from an intertidal sandflat in the Jade Bay (German Bight, North Sea)

Harpacticoid copepod assemblages from an intertidal sandflat in the Jade Bay (German Bight, North Sea) were investigated during a snapshot study, uncovering a relatively high small-scale organismic diversity: 1952 adult Harpacticoida of 32 species were recorded, belonging to 19 genera and 13 families. With 1232 adult specimens (63.1 %), Ectinosomatidae were the most abundant family, containingPseudobradya minor (T. & A.Scott) as the dominating species (57.4 %). For five species,Dactylopusia vulgaris (Sars),Remanea arenicola Klie,Mesochra pygmaea (Claus),Arenopontia subterranea Kunz, andEnhydrosoma gariene Gurney, the distributional range along the German coast line was extended to the area west of the river Elbe. Two species,Arenosetella tenuissima (Klie) andPseudobradya beduina Monard, were recorded for the first time in the Jade region. Most species recorded in our study are typical inhabitants of interridal sandy and/or muddy environments. Taking into account different aspects of diversity (species richness: species numbers, estimated species numbers by Jack-knife 1 and 2, species richness plots; heterogeneity: Shannon index, rarefaction curves; phylogenetic/taxonomic relationship: taxonomic distinctness) we found only minor diversity differences between four investigated small spatial scales (circles from 18 cm to 20 m diameter). Hypothesis [a] stating increasing diversity with increasing scale had to be rejected. This unexpected result could be caused by the presence of a mosaic of more or less randomly arranged micropatches of species over the sampling domain. Obviously, all citcles were more or less within the range of a single ecological scale. A slight diversity change at the 20 m scale, mainly based on lower species density, may be due to changing tide, or to a beginning overlap of small-scale random micropatches by a larger-scale environmental pattern. Since we found only minor diversity changes from the smallest (centimetres) to the largest investigated scale (tens of metres), biotic and/or abiotic factors and processes acting at spatial scales of centimetres are assumed to be of special relevance for intertidal harpacricoid diversity. Hypothesis [b] of no significant harpacticoid assemblage differences between the investigated scales was tested by ANOSIM for two similarity measures, leading to different results. Cosine similarity revealed no significant difference in assemblage composition between all possible pairwise combinations of circles, whereas [b] had to rejected for Bray-Curtis dissimilarity which produced significant results for two pairs (A/D, C/D). The difference between the test results is suggested to be caused by a lower species density in circle D, since Bray-Curtis dissimilarity is separating similar monitoring units if the difference is only due to multiples in abundance (Pfeifer et al. 1998).

An examination of the spatial and temporal generality of the influence of ecosystem engineers on the composition of associated assemblages

The present study evaluated the generality of ecosystem engineering processes by examining the influence of sympatric burrowing shrimps (Callianassidae) and intertidal seagrasses (Zosteraceae) on benthic assemblage composition in two temperate regions, south-eastern New Zealand and north-western U.S.A. In each region, intertidal macrofauna assemblage composition was determined at sites of different burrowing shrimp/seagrass density and where both species co-occured, in three different size estuaries/tidal inlets, on two occasions. Results from both regions showed that the presence of shrimps and seagrasses consistently influenced the composition of the associated infaunal assemblages at all sites, in both summer and winter. Macrofauna assemblages at shrimp sites were significantly different to those at seagrass-only and mixed sites, whereas the composition of the latter sites was similar. The differences observed between sites were best explained by sediment variables. In New Zealand, % fines and seagrass debris showed the highest correlation to differences in assemblage composition, and in the U.S.A. % fines, % carbon and sediment turnover (by shrimp) appeared to be the most important environmental parameters measured. Four to six taxa exhibited the greatest discriminating significance (including corophiid amphipods, spionid polychaetes and oligochaetes) for dissimilarities in assemblage composition observed at the different sites, with generally lower abundances at shrimp than at seagrass sites. The present study highlights the functional importance of seagrasses and bioturbating shrimps as ecosystem engineers in soft-sediment environments, and reveals the generality of their influence on associated macro-invertebrate assemblages. The findings also allow for further development of a heuristic model for ecosystem engineering by shrimp and seagrass which indicate that numerical models that aim to explore the relationship between ecosystem engineer populations and habitat modification should be expanded to capture the interaction of co-occurring engineers and be both spatially and temporally explicit.

Body size, not other morphological traits, characterizes cascading effects in fish assemblage composition following commercial netting

Traits used to group species and generalize predator–prey interactions can aid in constructing models to assess human impacts on food webs, especially in complex, species-rich systems. Commercial netting has reduced populations of large-bodied piscivores in some lagoons of a Venezuelan floodplain river, and cascading effects result in distinct prey fish communities in netted and unnetted lagoons. In 2002 and 2003, we sampled assemblages of prey fishes in netted and unnetted lagoons and tested whether fish size and (or) other morphological characteristics were associated with differences in assemblage composition. In both years, prey fish assemblages in netted lagoons were dominated numerically by larger species. We used geometric morphometric methods to test for a relationship between species morphological characteristics and found that neither overall morphological ordination nor specific morphological traits could be used to distinguish among assemblages. Thus, size was the only variable that was useful in explaining differences in assemblage composition. Even in this species-rich river with a complex food web, size-structured predator–prey interactions apparently influence community-level patterns and can be used to characterize human impacts.

Grassland Leafhoppers (Hemiptera: Auchenorrhyncha) as Indicators of Habitat Condition – A Comparison of between-site and between-year differences in Assemblage Composition

The Auchenorrhyncha (leafhoppers) show great potential as indicators of grassland habitat quality, which would make them useful as a conservation tool. However, they are known to have labile populations. The relative importance of site identity and the year of sampling in the composition of leafhopper assemblages on chalk grassland are assessed for two sets of sites sampled twice. The study included a total of 95 sites (one set of 54, the other of 41), and demonstrated that for both sets the vegetation community and geographical location had high explanatory value, while the influence of year was small. The conclusion is that, notwithstanding population fluctuations, the leafhopper assemblages are a good indicator of habitat quality, and represent a potentially valuable tool in grassland conservation and restoration.

Short‐term development of ambrosia and bark beetle assemblages following a windstorm in French broadleaved temperate forests

Abstract: In most temperate deciduous forests, windstorm is the main source of dead wood. However, the effects of this natural disturbance on ambrosia and bark beetle communities are poorly known. In managed oak‐hornbeam forests storm‐damaged in France in 1999, we sampled ambrosia (and second bark beetles) by ethanol‐baited window‐flight traps in 2001. By comparing uncleared gaps, undisturbed closed‐canopy controls and seedling‐sapling stands, we investigated the short‐term effects of gap formation, gap size and surrounding landscape to provide a snapshot of scolytid response. Contrary to expectations, neither the abundance nor the richness of ambrosia beetle species was significantly higher in gaps than in undisturbed stands. Few responses in abundance at the species level and only a slight difference in assemblage composition were detected between gaps and closed‐canopy controls. Gaps were more dissimilar from seedling‐sapling stands, than from closed‐canopy controls. More scolytid individuals and species were caught in gaps than in seedling‐sapling stands. Mean local and cumulative richness peaked in mid‐size gaps. Only mid‐size gaps differed from closed‐canopy controls in terms of species composition. We identified generalist gap species (Xyleborus saxesenii, X. cryptographus), but also species significantly more abundant in mid‐size gaps (Platypus cylindrus, Xyloterus signatus). The faunistic peculiarity of mid‐size gaps seemed to be partly related to a bias in oak density among gap size classes. Few landscape effects were observed. Only the scolytids on the whole and X. dispar were slightly favoured by an increasing density in fellings at the 78 ha scale. We did not find any correlation between scolytid abundance and the surrounding closed‐forest percentage area. We confirmed that temperate, deciduous, managed stands did not come under threat by ambrosia and bark beetle pests after the 1999 windstorm. Nonetheless, our data stressed the current expansion in Western Europe of two invasive species, X. peregrinus and especially X. germanus, now the predominant scolytid in the three oak forests studied.

Patterns of habitat segregation among large fishes in a Venezuelan floodplain river

Distribution and abundance of large fishes (SL>100 mm) in the río Cinaruco, a floodplain river in the Venezuelan llanos, were examined by gill net sampling in four habitat types: sand banks, backwater creeks, floodplain lagoons, and river channel. Sampling was standardized using nets (25 m x 2 m) of three mesh sizes set for 24-h periods. Based on data from >10,000 hours of gill netting over three years, there were significant differences in assemblage composition among the four habitats. Pair-wise comparisons suggested differences in assemblage composition between all pairs of habitats except creeks and lagoons. Differences in assemblage composition likely arose from species-specific habitat affinities. For example, 21 taxa were collected from both creeks and lagoons, but not from sand banks or the main river channel; each of these 21 taxa were associated with particular features characteristic of creeks and lagoons (e.g. abundant detritus). Assemblage structure also could be influenced by predation or other biological interactions, but mechanistic experiments are needed to evaluate this hypothesis. Assemblage composition was highly variable within all habitat types, likely the result of spatial and temporal heterogeneity associated with seasonal hydrology. Long distance migrations by prochilodontids and other taxa contributed to higher CPUE during the rising-water period of May 2002. Data from this study will provide a baseline to assess changes in the abundance and distribution of large-bodied fishes in response to increasing impacts from illegal commercial fishing in this region.

Syntrophic-methanogenic associations along a nutrient gradient in the Florida Everglades.

Nutrient runoff from the Everglades Agricultural Area resulted in a well-documented gradient of phosphorus concentrations in soil and water, with concomitant ecosystem-level changes, in the northern Florida Everglades. It was recently reported that sulfate-reducing prokaryote assemblage composition, numbers, and activities are dependent on position along the gradient (H. Castro, K. R. Reddy, and A. Ogram, Appl. Environ. Microbiol. 68:6129-6137, 2002). The present study utilized a combination of culture- and non-culture-based approaches to study differences in composition of assemblages of syntrophic and methanogenic microbial communities in eutrophic, transition, and oligotrophic areas along the phosphorus gradient. Methanogenesis rates were much higher in eutrophic and transition regions, and sequence analysis of 16S rRNA gene clone libraries constructed from samples taken from these regions revealed differences in composition and activities of syntroph-methanogen consortia. Methanogens from eutrophic and transition regions were almost exclusively composed of hydrogenotrophic methanogens, with approximately 10,000-fold-greater most probable numbers of hydrogenotrophs than of acetotrophs. Most cultivable strains from eutrophic and transition regions clustered within novel lineages. In non-culture-based studies to enrich syntrophs, most bacterial and archaeal clones were either members of novel lineages or closely related to uncultivated environmental clones. Novel cultivable Methanosaeta sp. and fatty acid-oxidizing bacteria related to the genera Syntrophomonas and Syntrophobacter were observed in microcosms containing soil from eutrophic regions, and different lines of evidence indicated the existence of novel syntrophic association in eutrophic regions.

Relationship between topographic heterogeneity and vegetation patterns in a Californian salt marsh

Abstract:Questions: Are species richness and species abundances higher in the presence of tidal creeks? Do species richness and species abundances vary with plot size?Location: Intertidal plain of Volcano Marsh, Bahia de San Quintin, Mexico.Methods: We analysed vegetation patterns in large areas (cells) with tidal creeks (+creek) and without (‐creek). We surveyed vegetation cover, microtopography, habitat type, and distance to creeks in nested plots of five sizes, 0.1, 0.25, 1, 2.5, and 10 m2.Results: Species richness, frequency, cover, and assemblages differed between ±creek cells. Richness tended to be higher in +creek cells, and cover and frequency of individual species differed significantly between ±creek cells. We found consistent patterns in vegetation structure across plot sizes. We encountered 13 species that occurred in 188 unique assemblages. The most common assemblage had six species: Batis maritima, Frankenia salina, Salicornia bigelovii, S. virginica, Salicornia spec. and Triglochin concinna. This assemblage occurred in ±creek cells and at all spatial scales. Of the most common assemblages all but one were composed of multiple species (3–9 species/plot).Conclusions: The persistence of vegetation patterns across a 100‐fold range in spatial scale suggests that similar environmental factors operate broadly to determine species establishment and persistence. Differences in assemblage composition result from variation of frequency and cover of marsh plain species, particularly Suaeda esteroa and Monanthochloe littoralis. The recommendation for restoration of Californian salt marshes is to target (and plant) multi‐species assemblages, not monocultures.

Classification and evaluation of spider (Araneae) assemblages on environmentally sensitive areas in Northern Ireland

Spiders have been collected as part of a biodiversity monitoring programme on environmentally sensitive areas (ESAs) in Northern Ireland initiated in 1993. Work to date on spiders in Ireland has consisted mainly of the cataloguing of County records. This paper furthers this work by classifying spider assemblages according to the habitat on which they were trapped. A total of 64 205 individuals of 184 species have been trapped using pitfalls representing almost half of the known Irish species. Distinct spider assemblages were recognisable on heather moorland, in woodland and on species-rich and species-poor grasslands. Geographical differences in assemblage composition were discernible. The number of records for each species was used to construct a provisional set of species quality scores to rank sites accordingly. Heather moorland harboured the highest mean number of species per site whilst ash woodland in County Fermanagh had the highest species quality score per site based on the number and rarity of spiders. Species-poor grassland had the lowest numbers of spider species with the lowest species quality scores due to their relative abundances. The scoring system used in conjunction with traditional phytosociological studies adds an important dimension to the evaluation of biodiversity on a monitoring site. Scores are a valuable tool for the future evaluation of monitored sites. Our results highlight the importance of heather moorland and woodland as plant communities and as unique habitats for specialist spider species.

EPIPHYTIC FORAMINIFERA ALONG A CLIMATIC GRADIENT, WESTERN AUSTRALIA

The presence of Posidonia australis seagrass habitat along 1000 km of the Western Australian coast provides an opportunity to study variation in epiphytic foraminiferal populations along a climatic gradient. Epiphytic foraminifera were collected in summer and winter from three nearshore shallow-water sites, which span a north-to-south gradient in climate from subtropical semi-arid to subtropical humid. Living epiphytic assemblages at each geographic site are distinct. Warmer water assemblages are characterized by Peneroplis spp. Vertebralina, Amphisorus and Marginopora , whereas Lamellodiscorbis and Rosalina spp characterize cooler water assemblages. The differences in assemblage composition partly reflect a north-to-south change in abundance of species related to climate, but also reflect local factors. Trends related to the climatic gradient include a decrease in miliolid and buliminid specimens and taxa, as well as a decrease in species with tropical affinity from north-to-south. Seasonal sampling at each geographic site also shows a decrease in miliolid and buliminid specimens and taxa, as well as a decrease in species with tropical affinity between summer and winter. This suggests that both regional and seasonal differences in epiphytic foraminiferal populations reflect a spatial vs. temporal response to change in sea temperature. Porcellaneous taxa are particularly sensitive to both regional and seasonal changes in sea temperature and appear to be good indicators of climatic setting. Using selected and critical species of foraminifera, it is possible to divide the subtropical region of Western Australia, traditionally viewed as a single biogeographic province, into at least two sub-climatic regions. Such refinement would be useful for interpreting paleoclimatic and paleoenvironmental settings of fossil assemblages.

Effect of patch size and in-patch location on the infaunal macroinvertebrate assemblages of Zostera marina seagrass beds.

Much recent work on patch-occupancy dynamics has been concentrated in terrestrial ecosystems, with few examples evident from soft-sediment marine habitats. Seagrass landscapes have recently been recognised to be potentially ideal marine models for the study of such ecological concepts. Infaunal macroinvertebrate assemblages of two patch sizes of the seagrass Zostera marina were compared: small (<15 m diameter) and large (>30 m diameter), using an unreplicated random block design. Further comparison was made between infaunal assemblage composition at the edge and centre of each patch. Univariate statistical analysis of data indicated significantly greater total numbers of taxa in samples from large patches than in small. Multivariate analyses indicated significant differences in assemblage composition due to both patch size and in-patch location, and revealed that differences were due to small changes in the relative abundances of many taxa. Possible mechanisms underlying the observed variations of assemblage composition with patch size and in-patch location are discussed. Although the present results support some of the theories relating to the control of infaunal assemblage composition, explanations are not applicable across all taxonomic groups. At the scale of the present study, seagrass patch size and edge-effects appear to be less significant than 'regional' factors, which relate to relatively small variation in environmental parameters, for the structuring of infaunal macroinvertebrate assemblages.

Spatial and temporal patterns of invertebrate drift in streams draining a Neotropical landscape

1. Invertebrate drift in streams draining a tropical landscape in Costa Rica was studied to assess differences in assemblage composition above and below a major gradient break in geomorphic landform and to assess temporal patterns of drift in lowland reaches below the gradient break. The gradient break (∼50 m a.s.l.) is the point at which the foothills of the Costa Rican Cordillera Central (piedmont) merge with the Caribbean coastal plain (lowlands). 2. Spatial patterns were assessed along two streams by sampling drift over 24 h once a month for 3 months in both the piedmont (90 m a.s.l.) and lowlands (30 m a.s.l.). Temporal patterns of drift were assessed through monthly diel sampling of three lowland sites over 8–10 months, encompassing both ‘dry’ (&lt;400 mm precipitation per month, November to May) and wet (July to October) seasons. 3. Drift composition was insect dominated in piedmont sites and larval shrimp dominated in the lowlands. Percent similarity of assemblages between piedmont and lowland sites was low (range 26–43%) because of high larval shrimp densities in lowland versus piedmont sites. 4. Drift densities were higher during night than day, with peaks at sunset on all dates and at all sites. Diel patterns in drift agree with previous observations for the study area and support the ‘risk of predation’ hypothesis. 5. Analysis of monthly patterns in lowland sites showed high variability in drift densities; however, all major taxa were found every month. Overall, there was a trend for high invertebrate densities during the ‘dry’ season, but these trends were not significant. 6. Observed changes in drift composition support the concept of river zonation, which predicts a change in community composition along the stream continuum due to geomorphic features. Drift at lowland sites below the gradient break was dominated by shrimps, which are linked to marine environments via their migratory behaviour.

Assessment of an ecoregion approach for classifying macroinvertebrate assemblages from streams in Victoria, Australia

An interim biogeographic regionalization for Australia (IBRA) divided the state of Victoria into 10 ecoregions or zones. The degree to which differences in the composition of stream macroinvertebrate assemblages (at 199 sites throughout the state) matched this a priori regionalization was determined by analysis of similarities (ANOSIM) of Bray–Curtis similarity measures. ANOSIM showed that although there was some overall difference in macroinvertebrate composition among the 10 ecoregions only 3 of the individual zones could be considered to have compositions that distinguished them from other zones. The remaining IBRA zones covered ∼60% of Victoria, but showed few differences in composition. The levels of difference in assemblage composition between the 25 catchments within Victoria or between the 11 site groups derived from cluster analysis were clearly greater than that for the IBRA zones. Thus IBRA does not provide a reliable classification of macroinvertebrate assemblages in Victoria.

Invertebrate conservation at the interface between the grassland matrix and natural Afromontane forest fragments

Diversity patterns of amphipods, carabid beetles and ants were investigated in five naturally-fragmented Afromontane forest remnants, and in the surrounding grassland matrix. Forests were architecturally similar. In contrast, grasslands surrounding these forests are subject to great differences in anthropogenic impacts. Consequently, transition from forest to grassland ranged from being abrupt (heavy disturbance) to gradual (little disturbance). Significantly different mean numbers of carabid individuals and species were captured between sites and multivariate analyses showed clear separation in carabid assemblage-structure with level of disturbance. Carabids were, furthermore, significantly more diverse in forests, compared to grasslands. Ants, however, were equally species rich between sites but were significantly more abundant and species rich in grasslands than forests. Amphipods, represented here by a single species, Talistroides africana, was significantly less abundant at highly disturbed sites and significantly more abundant in forests than grasslands. Results support the hypothesis that the dynamics of remnants are influenced by their surrounding landscape. Here, the dynamics of amphipods and carabids (predominantly forest taxa) were influenced by different disturbance regimes in grasslands surrounding these forests. Epigaeic ants, a predominantly grassland taxon here, also showed significant differences in assemblage-composition between sites with varying disturbance. Conserving Afromontane grasslands should be of prime concern because this will include the protection of forest/grassland ecotones and forest remnants.