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6 results on '"species assemblages"'

1. Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia

Author

Hans Malicky, Alemayehu Wubie, Gernot K. Englmaier, Yonas Terefe, Wolfram Graf, Daniel S. Hayes, Patrick Leitner, Genanaw Tesfaye, Herwig Waidbacher, Paul Meulenbroek, and Aschalew Lakew

Subjects
geography, geography.geographical_feature_category, biology, Ecology, Biodiversity, Fluvial, Tropics, Ecotone, Aquatic Science, biology.organism_classification, freshwater ecoregions, species assemblages, indicator species, Caddisfly, Indicator species, Tributary, Africa, Ecosystem, biogeography, biodiversity
Abstract

Primary Research Paper Specific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropics info:eu-repo/semantics/publishedVersion

Published
2020

2. Landscape Ecology / Diversity of bumblebees, heteropteran bugs and grasshoppers maintained by both: abandonment and extensive management of mountain meadows in three regions across the Austrian and Swiss Alps

Author

Thomas Frank, Bärbel Pachinger, David Brandl, Arne Arnberger, Andreas Bohner, Leopold Sachslehner, Johann G. Zaller, Ronnie Walcher, and Johannes Karrer

Subjects
0106 biological sciences, Herbivore, Ecology, biology, Geography, Planning and Development, biology.organism_classification, 010603 evolutionary biology, 01 natural sciences, Mountain grassland, Heteroptera, 010602 entomology, Habitat, Species assemblages, Pollinator, Abundance (ecology), Orthoptera, Species richness, Landscape ecology, Grasshopper, Bumblebee, Nature and Landscape Conservation, Bombus sp
Abstract

Context Abandonment of extensively managed meadows is an ongoing global challenge in recent decades, particularly in mountain regions, and directly affects plant diversity. However, the extent to which plant diversity further affects associated insect pollinators or herbivores is little investigated. Objectives We focused on the effects of abandonment of mountain meadows on species richness and assemblages of bumblebees, bugs and grasshoppers. Specifically, we investigated the influence of vegetation cover, flower cover, plant richness and surrounding landscape on the three insect groups. Methods Species richness, abundance and species assemblages of bumblebees, bugs and grasshoppers were surveyed in one Swiss and two Austrian regions: three meadows which had been abandoned for 1560 years, and three extensively managed meadows (mown once a year, no use of fertilizers). We surveyed bumblebees and bugs by sweep net, and grasshoppers using the time-effective soundscape approach. Results Bumblebee species richness and abundance were significantly higher in managed meadows, whereas bug and grasshopper richness and abundance showed no differences between both management types. Managed and abandoned meadows harboured significantly different species assemblages of bugs and grasshoppers, but not of bumblebees. Increasing flower cover and plant richness increased bumblebee richness, but correlated negatively with richness of bugs. Surrounding open landscape positively affected bugs. Caelifera positively correlated with surrounding forest cover and negatively with vegetation cover. Vegetation cover positively affected Ensifera. Conclusions Abandoned and extensively managed meadows are important habitat types for the conservation of the three insect groups, thus suggesting the maintenance of both habitat types within mountain landscapes. (VLID)2786607

Published
2017

3. Dyke-slotting initiated rapid recovery of habitat specialists in floodplain mollusc assemblages of the Elbe River, Germany

Author

Rumm, A., Foeckler, F., Deichner, O., Scholz, Mathias, Gerisch, M., Rumm, A., Foeckler, F., Deichner, O., Scholz, Mathias, and Gerisch, M.

Abstract

Dyke openings are regarded as suitable measures for restoring biodiversity and ecosystem functioning in degraded floodplains. Nevertheless, only few studies evaluate the effects and success of such measures on biodiversity. The present work analyses the influence of one of the first dyke-slotting projects carried out along the Middle Elbe River (Germany) on floodplain mollusc assemblages. By applying a before-after-reference-control-impact-monitoring design, we specifically tested how species diversity and composition responded to the restoration measure. Floodplain reconnection led to a considerable increase in mollusc diversity. However, the overall community turnover was rather small only present among species with high soil humidity preferences. They mainly profited from the frequent floodings shifting species composition to be more hygrophilous and floodplain characteristic. Moderately hygrophilous and desiccation tolerant species were almost not affected by the dyke-slotting. Presumably, this can be explained by the already similar species composition of the active reference and the reactivated floodplain due to a high seepage water influence. So far, this indicates a successfully initiated recovery process. All in all, our results emphasize the crucial need of long-term monitoring to reveal the full ecological effects of restoration measures and the consideration of diversity-, community-, and species-level responses to evaluate restoration success

Published
2016

4. Species richness and distribution of copepods and cladocerans and their relation to hydroperiod and other environmental variables in Donana, south-west Spain

Author

Dagmar Frisch, Enrique Moreno-Ostos, and Andy J. Green

Subjects
geography, geography.geographical_feature_category, Marsh, biology, Ecology, temporary waterbodies, hydroperiod, Wetland, Vegetation, Aquatic Science, Guadalquivir marshes, biology.organism_classification, Zooplankton, species assemblages, Crustaceans, Habitat, Abundance (ecology), Species richness, Copepod
Abstract

Twenty-five sites located in five wetland zones within Donana, south-west Spain were studied for copepod and cladoceran species richness and composition in relation to habitat characteristics from January to March 2004. The c-diversity of copepods and cladocerans combined varied between wetland zones, which differed significantly in conductivity, surface area and abundance of vegetation. However, there were no significant differences between zones in local species richness of either copepods or cladocerans or the two combined. Species richness was significantly higher in sites with intermediate hydroperiods (duration between 3 and 5 months) than in sites with shorter or longer hydroperiods. CCA analyses performed separately for copepods and cladocerans extracted conductivity, surface area, and vegetation cover as the main factors structuring species composition of both groups. Ours is one of the first studies of zooplankton in the natural marshes of the Donana World Heritage Site, and we recorded five species new to the Donana area

Published
2006

5. An evaluation of randomization models for nested species subsets analysis.

Author

Cook RR and Quinn JF

Abstract

Randomization models, often termed "null" models, have been widely used since the 1970s in studies of species community and biogeographic patterns. More recently they have been used to test for nested species subset patterns (or nestedness) among assemblages of species occupying spatially subdivided habitats, such as island archipelagoes and terrestrial habitat patches. Nestedness occurs when the species occupying small or species-poor sites have a strong tendency to form proper subsets of richer species assemblages. In this paper, we examine the ability of several published simulation models to detect, in an unbiased way, nested subset patterns from a simple matrix of site-by-species presence-absence data. Each approach attempts to build in biological realism by following the assumption that the ecological processes that generated the patterns observed in nature would, if they could be repeated many times over using the same species and landscape configuration, produce islands with the same number of species and species present on the same number of islands as observed. In mathematical terms, the mean marginal totals (column and row sums) of many simulated matrices would match those of the observed matrix. Results of model simulations suggest that the true probability of a species occupying any given site cannot be estimated unambiguously. Nearly all of the models tested were shown to bias simulation matrices toward low levels of nestedness, increasing the probability of a Type I statistical error. Further, desired marginal totals could be obtained only through ad-hoc manipulation of the calculated probabilities. Paradoxically, when such results are achieved, the model is shown to have little statistical power to detect nestedness. This is because nestedness is determined largely by the marginal totals of the matrix themselves, as suggested earlier by Wright and Reeves. We conclude that at the present time, the best null model for nested subset patterns may be one based on equal probabilities of occurrence for all species. Examples of such models are readily available in the literature.

Published
1998
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6. The relationship between nested subsets, habitat subdivision, and species diversity.

Author

Cook RR

Abstract

Biotic assemblages are said to be nested when the species making up relatively species-poor biotas comprise subsets of the species present at richer sites. Because species number and site area are often correlated, previous studies have suggested that nestedness may be relevant to questions of how habitat subdivision affects species diversity, particularly with respect to the question of whether a single large, contiguous patch of habitat will generally contain more species than collections of smaller patches having the same total combined area. However, inferences from analyses of nestedness are complicated by (1) variability in degrees of nestedness measured in natural communities, (2) variability in species-area relationships, and (3) the fact that nestedness statistics do not account for the size of habitat patches, only in the degree of overlap among sites with different numbers of species. By comparing various indices of nestedness with a "saturation index" that more directly measures the effect of habitat subdivision, it is shown that the first two of these factors are not as important as the third. Whether a single large site or several smaller ones having the same total combined area maximizes species diversity is dependent on (1) overlap in species composition among sites and (2) the number of species per unit area in the different sites. Because nestedness indices do not account for species number at a site, they cannot accurately predict how habitat subdivision affects species diversity patterns. Still, nestedness analyses are important in that they indicate the degree to which rare species tend to be found in the largest, or the most species-rich, sites, patterns not revealed by the saturation index. Both types of analysis are important in order to obtain a more complete picture of how species richness and compositional patterns are influenced by habitat subdivision.

Published
1995
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