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Rich Habitats (rich + habitat)
Selected AbstractsThe distribution and diversity of amphibian fauna of Lake Nabugabo and surrounding areasAFRICAN JOURNAL OF ECOLOGY, Issue 2004M. Behangana Abstract Six major vegetation types surrounding Lake Nabugabo were sampled for amphibians. These types were: shoreline zone (habitat type code A) representing vegetation on the shoreline about 2 m from the shoreline; Miscanthidium violaceum (B); Eragrostis-Loudetia (C); swamp forest (D); Cyperus papyrus (E); and medium altitude evergreen forest (F). A total of 168 days were spent in the field with a total of 288 1 h counts. Forty-eight counts were carried out in each vegetation type. Sampling was carried out between 17.00 and 24.00 h to coincide with the time amphibians are very active. Twenty-four species were recorded during the study period. These account for about 27.9% of total number of amphibian species recorded in Uganda. Four families were identified, which included: Ranidae (12 spp.), Hyperolidae (8 spp.), Bufonidae (3 spp.) and Pipidae (1 sp.). There was substantial variation in observed species composition among vegetation types. The most species rich habitat was the Eragrostis-Loudetia vegetation zone (17 spp.), followed by the swamp forest zone (14 spp.), then the M. violeceum swamp (11 spp.) and the shoreline (10 spp.). The most species poor sites were C. papyrus swamp (6 spp.) followed by the medium altitude forest (7 spp.). In terms of species abundance, the swamp forest and the M. violecium zones were the most important amphibian habitats for the common species while the Eragrostis-Laudetia zone stood out as the most important for the rare species. From the data collected, it can be deduced that the three most important habitats for the conservation of amphibian fauna in the study area are the Eragrostis-Laudetia, M. violeceum and the swamp forest zones. [source] Widespread resistance of Mediterranean island ecosystems to the establishment of three alien speciesDIVERSITY AND DISTRIBUTIONS, Issue 5 2008Montserrat Vilà ABSTRACT Although some invasive plants are cosmopolitan, not all ecosystems are invaded to the same degree. Yet there is little experimental work on how ecosystem resistance to invasion at the establishment phase differs among ecosystems. We conducted two field sowing experiments in two consecutive years to examine establishment of the deciduous tree Ailanthus altissima, the succulent subshrub Carpobrotus spp. and the annual geophyte Oxalis pes-caprae in coastal dunes, shrublands and oldfields in more than 200 sites across six Mediterranean Basin islands differing in climatic conditions and local species richness. Establishment success (i.e. percentage of plots with at least one seedling) and rates (i.e. seedling to sown seed ratio) were low, especially for Ailanthus even when accounting for differences in seed viability. Oxalis was capable of producing a new cohort of seedlings the year following planting. By contrast, all Ailanthus seedlings and half the Carpobrotus seedlings died following the first summer. Differences in establishment success and rates among ecosystems were species-, island- and year-dependent. Differences in precipitation and mean temperature were associated with differences in establishment rates across sites. Establishment rates tended to be positively correlated with cumulative precipitation and negatively with mean Ta. Unexpectedly, native species richness was not a good predictor of seedling establishment, except for higher Oxalis establishment success in species rich habitats. By conducting field sowing tests at multiple sites across a region we found that except for Oxalis, Mediterranean island ecosystems are quite resistant to invader establishment. These results suggest that differences in the degree of invasion between ecosystems and islands might be more dependent upon the influence of invasion event factors (e.g. propagule pressure) or factors acting at a later life-history stages rather than differences in the resistance imposed by ecosystems to invader recruitment. Moreover, our results support the notion that in Mediterranean ecosystems invasions are highly idiosyncratic events and strongly dependent on water availability conditions. [source] Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South AfricaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2002S. Tooth Abstract Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ,1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel-bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ,1·10,1·34), and floodplains are restricted in width. Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd. [source] Habitat size and number in multi-habitat landscapes: a model approach based on species-area curvesECOGRAPHY, Issue 1 2002Even Tjørve This paper discusses species diversity in simple multi-habitat environments. Its main purpose is to present simple mathematical and graphical models on how landscape patterns affect species numbers. The idea is to build models of species diversity in multi-habitat landscapes by combining species-area curves for different habitats. Predictions are made about how variables such as species richness and species overlap between habitats influence the proportion of the total landscape each habitat should constitute, and how many habitats it should be divided into in order to be able to sustain the maximal number of species. Habitat size and numbers are the only factors discussed here, not habitat spatial patterns. Among the predictions are: 1) where there are differences in species diversity between habitats, optimal landscape patterns contain larger proportions of species rich habitats. 2) Species overlap between habitats shifts the optimum further towards larger proportions of species rich habitat types. 3) Species overlap also shifts the optimum towards fewer habitat types. 4) Species diversity in landscapes with large species overlap is more resistant to changes in landscape (or reserve) size. This type of model approach can produce theories useful to nature and landscape management in general, and the design of nature reserves and national parks in particular. [source] | ||||||||||