Elevational changes in vascular plants richness,diversity, and distribution pattern in Abune Yosef mountain range,Northern Ethiopia

The aim of this research is to investigate the patterns of vascular plant species richness,diversity,and distribution along an elevation gradient in the Abune Yosef mountain range,Ethiopia.Preferential systematic sampling was employed to collect vegetation and environmental data along the elevation gradient.We found that plant species richness declines monotonically from low to high elevations.Specifically,vascular plant species richness and diversity were lower in the Afroalpine grassland(high elevation)than in the Dry evergreen Afromontane forest and Ericaceous forest(low elevations).In contrast,endemic vascular plant richness was significantly higher in the Afroalpine grassland than in the Dry evergreen Afromontane forest and Ericaceous forest.Elevation showed a significant impact on the richness,diversity,and endemism of vascular plants.According to Sorensen's coefficient,the similarity between Dry evergreen Afromontane forest and Ericaceous forest vegetation types is higher(32%)than the similarity between Ericaceous forest and Afroalpine grassland(18%).Only 5%similarity was recorded between the Dry evergreen Afromontane forest and Afroalpine grassland.Growth forms showed different elevationai richness patterns.Trees and liana increased monotonically up to 3300 m.Shrub and herb richness patterns followed a hump-shaped and inverted hump-shaped pattern along the elevation gradient.The elevation patterns of vascular plant species richness,diversity,and growth form in the present study may be attributed to differences in management intensity,spatial heterogeneity,microclimatic variations,and anthropogenic disturbances.     

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The variance test, originally proposed for testing species associations, is used to test whether species richness is more or less variable than expected under the null model of no species interactions. Species richness is more variable than expected in some fields, and less variable than expected in other fields at the Cedar Creek Natural History Area in Minnesota. High variance in species richness may be caused by variability in competitive exclusion rates or small-scale environmental heterogeneity. Low variance in species richess may occur if the community is saturated with species, or if species-rich areas have high local competitive exclusion rates. Results of the variance test depend somewhat on quadrat size, and can be used to select study sites and quadrat sizes for further research on the nature of variation in species richness.     

Drought and biodiversity in Grasslands

Summary The local species richness of four different grassland fields fell an average of 37% during a 1988 drought that decreased above-ground living plant mass by an average of 47%. Despite the return to more normal plant mass and precipitation during the next two years, there was no significant recovery in species richness in the 46 permanent plots, suggesting that local species richness became recruitment limited. The drought led to the loss of annual species independent of their abundance. For perennial grasses, perennial forbs, legumes and woody species, the probability of a species being lost from a plot was significantly negatively correlated with its predrought abundance. These results demonstrate that environmentally extreme conditions can limit species richness by causing the local extinction of rare species. Because droughts of this intensity occur about every 50 years in the prairie, periodic drought may have limited prairie diversity. Moreover, if the accumulation of greenhouse gases leads to a more variable or extreme climate, it could cause increased rates of species extinctions.     

The relationship between productivity and multiple aspects of biodiversity in six grassland communities

Biodiversity is a multifaceted concept but most studies examining the association between the biodiversity of a community and its productivity focus only on species richness. Consequently, studies are needed to examine how other facets of biodiversity vary with productivity if we want to have a better understanding of the distribution of biodiversity across our planet. We evaluated how a number of biodiversity measures (species richness, evenness, dominance, rarity, Simpson’s diversity, and Shannon–Weiner diversity) varied across natural productivity gradients at 6 grassland sites in the continental US. Variation in productivity did not account for a substantial amount of variation in any measure of biodiversity at small spatial scales (≈1 m²) at most sites. When productivity accounted for substantial variation in biodiversity, different measures of biodiversity responded to productivity in different ways. For example, dominance changed in a U-shaped fashion along a productivity gradient whereas richness increased in an asymptotic fashion. Consequently, diversity indices, which account for both species richness and evenness, varied in a hump-shaped fashion along the productivity gradient. Our results highlight that an exclusive focus on the association between species richness and productivity provides an incomplete picture of how a community’s biodiversity is related to its functioning.     

The ground beetle fauna (Coleoptera:Carabidae) of abandoned fields, as related to plant cover, previous management and succession stage

This study describes differences in species richness, diversity and composition of Carabidae in gradients from recently abandoned, non-grazed fields over stages of overgrowth into forest on formerly agricultural land in a large, sandy outwash plain, south Sweden. Totally 80 pitfall traps, (4 succession stages, each represented by 4 sites; 5 traps per site) installed on 29 March 2006 were emptied continuously until 1 November. Succession stages were: 7–10 y old fallows after cereals with thin and low vegetation of small perennial and annual herbs (Ia), 7–10 y old fallows abandoned as lay with a rich plant cover of broad-leaved grasses and herbs (Ib), 20–25 y old fallows with a shrub layer of colonising pine and narrow-leaved grasses (II), and ca 80 y old pine stands planted on originally cultivated ground with a rich shrub layer but lacking herbaceous plants (III). A total of 14,068 individuals of 71 carabid species were captured. Species richness was highest in stage Ib, whereas Shannon species diversity was highest in Ia. Both species richness and diversity were lowest in III, sites II being intermediate. Total number of individuals captured site⁻¹ was low in III, being highest in Ib. Mean body weight and total dry mass of species, however, increased with succession stage. Amara and Harpalus species were most common in Ia but important also in Ib, with large differences in species composition between the two stages. These genera were almost lacking in III, where Carabus spp. and Pterostichus niger dominated. The share of Calathus was highest in II, where C. fuscipes played a dominating role. P. versicolor dominated in Ib, whereas P. lepidus was quite common in all non-forest stages. Duration and intensity of capturing activity necessary to find most species of the sites are discussed. Many scarce or rare species in south Scandinavia were captured, mainly in Ib. Abandoned non-grazed fields are important hibernating and breeding refuges for many carabids. Using extensive and non-expensive management this ought to be considered as an additional alternative in environment conservation policy, which now usually recommends economically subsidised grazing on set-aside land.     

The impact of water-level regulation on littoral macroinvertebrate assemblages in boreal lakes

Regulation of lake water level for power production and flood control is among the major anthropogenic disturbances in boreal aquatic ecosystems. In Finland, over 300 lakes, representing one third of the total inland water area of the country, are artificially regulated. To study the effects of regulation on lake littoral macroinvertebrate communities, samples were taken from upper stony littoral and from lower soft bottom littoral habitats of 11 lakes with different regulation amplitudes (wintertime fall in water level 1.19–6.75 m). Twelve unregulated (wintertime fall in water level 0.11–0.55 m) lakes with otherwise similar characteristics were used as a reference. Non-metric Multidimensional Scaling ordinations showed that the composition of macroinvertebrate assemblages was strongly associated with the amplitude of water level regulation. Taxon richness also decreased with increasing intensity of regulation. Freezing and flushing of sediments in late winter are probably the most important factors leading to the impoverished littoral macroinvertebrate fauna. Invertebrates with long life cycle seem to be particularly vulnerable to unnatural water level fluctuation. Our results show that regulation of water level has a major impact on functionally significant lake littoral macroinvertebrates.     

Strong influence of long-distance edge effect on herb-layer vegetation in forest fragments in an agricultural landscape

In agricultural landscapes in central Europe, species richness of the herbaceous plant community may be compromised by processes associated with forest fragmentation, habitat loss, and management practices. We examined variability in species richness and composition of the herbaceous layer in 229 plots located in 23 forest fragments (0.1 to 255 ha), in a representative upland agricultural landscape in central Bohemia, in relation to the most important site environmental factors, edge effects, and site history. The influence of environmental factors on the composition of vegetation in the herb layer was evaluated using generalized additive models, which enabled us to analyze highly non-linear and non-monotonic relationships. Total species richness and number of red-listed and ancient forest species were significantly influenced by type of forest vegetation, light quality, soil pH, slope aspect, and distance from the forest edge. Implications of the significant explanatory variables corresponded well to previous findings, with the exception of distance from the forest edge, for which we found a positive relationship with species richness for distances up to 200 m toward the forest interior. Plant species with low colonization ability occupied plots with increasing frequency from edge to forest interior, while fast-colonizing species showed the opposite trend. Apart from the edge effect, forest continuity should be considered for its important contribution to the richness of ancient forest and red-listed species, whereas the effect of forest fragment size appeared to be generally weak. These results do not negate the importance of large forest fragments for the maintenance of herb layer species richness, but specifically emphasize the essential contribution of the core habitats of these forests. In summary, we showed that the negative effects of habitat fragmentation on the richness of ancient forest and red-listed species and on herb layer species in total can be largely attributed to either the edge effect itself or to aggregate effects of forest edge and forest continuity.     

Experimental effects of habitat fragmentation on old-field canopy insects: community, guild and species responses

We examined the effects of habitat fragmentation on the species distributions, guild membership, and community structure of old-field insects using a fine-scale experimental approach. A continuous 1-ha goldenrod field was fragmented into four treatments that varied in both patch size and degree of isolation. Each treatment was replicated four times and arranged in a Latin square design. Canopy insects in fragmented patches were sampled with sweep nets during early and late summer 1995. The species richness of insects was significantly lower in fragmented than in unfragmented treatments during July, but was similar among treatments in September. Overall community abundance showed no treatment effect during either month. We also found significant row and column effects, suggesting there was spatial heterogeneity in species richness and abundance apart from treatment effects. Differences in species richness during July were primarily due to the loss of rare species in highly fragmented plots. Overall abundance was less responsive to community change because deletions of rare species in fragmented areas were not detected in abundance analyses. Four feeding guilds showed different responses to fragmentation: the species richness of sucking herbivores and the abundance of parasitoids were significantly reduced by fragmentation but predators and chewing herbivores were largely unaffected. Analyses of a subset of individual species within guilds suggest that the greater effects of fragmentation on sucking herbivores and parasitoids may be due to the degree of habitat specificity of guild members. The effects of small-scale habitat fragmentation were therefore detectable at the level of community, guild, and individual species. Changes in species richness, guild structure and species distributions were likely due to differential effects of habitat alteration on individual movements and patch selection rather than dispersal or demographic change. Nonetheless, the selective loss of rare species, differential guild effects and changes in species occupancy that we found in this small-scale experiment are also factors that are likely to operate in fragmented habitats over broader spatial scales. Received: 11 May 1998 / Accepted: 27 September 1998     

Shoot biomass and species richness in relation to some environmental factors in a coastal dune area in The Netherlands

Shoot biomass, species richness and selected environmental factors were studied at Meijendel, a coastal dune area in The Netherlands. The relationship between species richness and shoot biomass of the stand could be best described by a unimodal curve, with the peak at 300 g m^–2. Measures of species richness were positively correlated with soil water, nitrogen and phosphorus.Shoot biomass showed a positive correlation with soil water, nitrogen and humus at low levels of shoot biomass.Nomenclature of phanerogams and plant community types follows Heukels & van Ooststroom (1973), and Westhoff & den Held (1969) respectively.Publication of the Meijendel comité new series: 76.     

Effects of river level fluctuation on plant species richness, diversity, and distribution in a floodplain forest in Central Amazonia

River levels in Central Amazonia fluctuate up to 14 m annually, with the flooding period ranging from 50 to 270 days between the rising and falling phases. Vast areas of forest along the rivers contain plant species that are well adapted to annual flooding. We studied the effect of flooding level on tree species richness, diversity, density, and composition in lake, river, and stream habitats in Jaú National Park, Brazil. 3051 trees >10 cm diameter (at 1.3 m diameter at breast height, dbh) were measured and identified in 25 10 m × 40 m randomly selected plots in each habitat. Ordination methods and analysis of variance results showed that forested areas near lakes had significantly lower species richness of trees than riverine and streamside habitats. Plot species richness and diversity were strongly negatively correlated with the water level and duration of flooding. The drier (stream) habitat had more total species (54 species of trees) and more unique species of trees (6 tree species) than the riverine (52 tree species; 3 unique species) and lake (33 tree species; 3 unique species) habitats. Species composition overlap among habitats was surprisingly high (42.6–60.6% overlap), almost one-third of the species were found in all three habitat types, and few species were unique to each habitat. We conclude that: (1) duration of flooding has a strong impact on species richness, diversity and plant distribution patterns; (2) most species are adapted to a wide range of habitats and flood durations; and (3) while flood duration may decrease local diversity, it also creates and maintains high landscape-scale diversity by increasing landscape heterogeneity. Received: 20 April 1997 / Accepted: 14 January 1999