Search Results

You are looking at 41 - 50 of 143 items for :

  • Biology and Life Sciences x
  • Refine by Access: All Content x
Clear All

Alpine grasslands harbour species-rich communities of plants and invertebrates. We examined how environmental variables and anthropogenic impact shape species richness and community structure of terrestrial gastropods in alpine grasslands in the Val Müstair (Eastern Alps, Switzerland). Gastropods were sampled using a standardised method at 76 sites spanning an elevation range from 1430 m to 2770 m. A total of 4763 specimens representing 52 species were recorded. Correspondence analysis based on presence/absence data revealed that the grassland gastropod community was structured in a complex way with elevation, wetness, grazing intensity and inclination of the sites as key factors, while abundance-based analysis identified the importance of the elevation and wetness of sites. Generalized linear model showed that species richness decreased with increasing elevation and increased with increasing soil pH. The grassland gastropod communities were characterized by a high beta diversity, as indicated by the SDR-simplex analysis. Species-specific traits of gastropods showed sensitivity to the environmental characters of the sites, as shown by a fourth-corner analysis.

Restricted access

We studied the vegetation of 54 sandy old-fields abandoned at different times. We first surveyed the vegetation in 1998 and developed predictions about the spontaneous succession using the chronosequence approach. Afterwards, we repeated the survey in 2000, 2001, 2002 and 2003, and based on this monitoring we tested the predictions of the chronosequence study. For both approaches, we analysed the changes in functional group composition during succession. According to the chronosequence study, the most important changes occurred in the youngest old-fields, abandoned 1–4 years ago: the species number and abundance of annuals, disturbance-requiring and anthropogenic species decreased, and those of perennials, grassland generalists, and species with low disturbance-tolerance increased. No changes were predicted for the older fields. The monitoring confirmed the predictions for the youngest old-fields. However, during the 5 years of monitoring several functional groups changed in their species number or abundance even on the older abandoned fields. Both of the methods showed that secondary succession on sandy old-fields is relatively fast. The chronosequence study provided a more static view of the processes, while the multi-year monitoring revealed that there were considerable inter-annual changes as well. With the yearly monitoring we can detect the effect of additional factors, such as land use changes (e.g., changes in grazing intensity) and yearly climate fluctuations on the direction and rate of secondary succession.

Restricted access

Bos primigenius , the wild aurochs is believed to be the ancestor of European domestic cattle, Bos taurus . The geography and climate of the Great Hungarian Plain were well suited for these large grazing animals in the Late Neolithic. Till now, there are just a few aurochs mtDNA fragments available from two geographically restricted area, the British Isles and Italy. To increase our knowledge about the genetics of the European aurochsen livestock, and to investigate the phylogenetic position of a late Neolithic aurochs, excavated from the Carpathian Basin, mitochondrial DNA was extracted from a fragment of corpus mandibulae using ancient-DNA techniques and a portion of mitochondrial hypervariable region was amplified by PCR. The resulting sequence was aligned with GenBank sequences of 11 aurochsen. Our new sequence is identical with the sequence of two British aurochs. The 6000-year-old Hungarian aurochs shows a mtDNA sequence pattern, that occurs only among 6–12,000-year-old North European aurochsen, and it does not occur among modern, domesticated cattle.

Restricted access

Hendricksen, R. E., Miller, C. P., Punter, L. D. (1999): Diet selection by cattle grazing tropical tallgrass pasture. Proceedings of the VI International Rangeland Congress. Townsville, Australia. pp. 222-223. Diet selection by cattle

Restricted access

Over millions of years there is a long-term increase in species richness, accompanied by substantial turnover in species composition. However, little is known about species temporal turnover over shorter, ecologically relevant time periods, such as years. In the present study, we examine the inter-annual temporal turnover in species composition in 100 m2 plots of the herbaceous layer in a submediterranean oak woodland over six years. We found that approximately half of the accumulated number of species over the six years is accommodated as temporal turnover. We also found that species temporal turnover in undisturbed control plots was not significantly different from that in plots where vegetation was recovering naturally without assistance, i.e., plots undergoing ecological succession. Only in the most disturbed (continuously overgrazed) plots temporal turnover was low to non-existent. We therefore suggest that diversity estimates based on a single year of observations may seriously underestimate species richness or the detrimental effects of disturbance, at least at the 100 m2 scale. Furthermore, we found that, with the exception of the heavily grazed plots, short-lived species (annuals and biennials) did not display significantly greater temporal turnover than long-lived (perennial) species. Our analysis also supports that the space for time substitution applies in the patterns of species turnover. Spatial species turnover was comparable to temporal turnover. Species that are observed in many plots are also present in many years, and vice versa. Also, the similarity in species composition decreased as the time period between observations increased, as is the case with distance decay. Overall we conclude that the patterns of species turnover in time resemble those in space, and thus temporal turnover makes an important contribution to total biodiversity that should not be ignored.

Restricted access

We study the structure of two contrasting alpine forest.pasture ecotones located in the Central Pyrenees (sites Ordesa and Tessó). We define ecotone structure as the spatial distribution of trees of different size classes and growth-forms, and the relationship between these aspects and the spatial distribution of understory vegetation and substrate. The studied ecotones are dominated by Pinus uncinata and have been little affected by recent anthropogenic disturbances (logging, grazing). One rectangular plot (30 x 140 m2) was located within each site encompassing treeline and timberline with its longest side parallel to the slope. The distribution of size and growth-form classes at Ordesa followed a clear sequence of increasing size downslope, from shrubby krummholz individuals to bigger arborescent trees. At Ordesa, regeneration was concentrated near the krummholz area and over rocky substrates. At Tessó, regeneration was abundant above the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. Detrended canonical correspondence analysis of tree and plant cover data, with respect to spatial location in the ecotone and substrate cover, demonstrated that elevation was an important factor controlling the distribution of trees and understory plants in both ecotones. Finally, k-means clustering with spatial constraint revealed abrupt spatial clusters along the slope at Ordesa. However, the ecotone at site Tessó was composed of elongated downslope spatial clusters suggesting greater spatial heterogeneity and subtle gradual changes due to other factors in addition to the altitudinal gradient (snow avalanches). These contrasting structures correspond well with the ecotone (sharp boundary, Ordesa) and ecocline (gradual transition, Tessó) concepts. This suggests the dominant role of different local environmental factors: wind at site Ordesa and avalanches at Tessó. Positive feedbacks, like facilitation among P. uncinata individuals (nurse effect), may maintain and intensify the sharpness of the ecotone at Ordesa.

Restricted access

Competing species often coexist, but the mechanisms allowing long-term coexistence are rarely tested via direct experimental manipulation. We experimentally tested the mechanisms of coexistence in a classic model system, laboratory microcosms in which two species of ciliate protists competed for bacteria. Previous work shows that the species used here compete for bacteria, but can coexist despite large differences in grazing ability. We tested three hypotheses that might explain this surprising coexistence: resource partitioning, chemically-mediated interference competition, and differential use of space. To test for resource partitioning, we conducted an experiment testing the effects of bacterial species richness and composition on the long-term outcome of competition. Manipulating bacterial diversity and composition alters the scope for resource partitioning. Despite strong evidence for differential resource use (e.g., the two ciliates shifted bacterial species composition in different ways), initial bacterial richness and composition did not affect the long-term outcome of competition. Remarkably, the competitive outcome was unchanged even when ciliates competed for a single bacterial species, indicating that the observed resource partitioning is irrelevant to the competitive outcome. In further experiments, we ruled out differential space use and chemically-mediated interference competition as explanations for this surprising coexistence. Coexistence of ciliates on a single bacterial species might reflect partitioning of intraspecific bacterial diversity, and/or osmotrophy or consumption of particulate detritus by the weaker competitor. The results show that this classic model system is not as well-understood as had been previously thought. More broadly, the results dramatically illustrate that merely observing “niche differences” between coexisting species is no evidence that those differences are either necessary or sufficient for long-term coexistence.

Restricted access

grasslands under grazed and non-grazed conditions in Tierra del Fuego. J. Veg. Sci. 12: 385-390. Vertical structure of wet grasslands under grazed and non-grazed conditions in Tierra del Fuego J. Veg

Restricted access

This study was carried out to compare composition, density and diversity of species between dryland and irrigated agroecosystems and between agroecosystems and the marginal grassland ecosystem in dry tropics. Main management characteristics of these ecosystems are: (1) Dryland cropping, low fertilizer input, rainfed (no irrigation) and seed sown rice; (2) Irrigated cropping, high fertilizer, water (irrigation) inputs, flooded rice by transplanting; (3) Grassland, post-rainy season herbage removal and light grazing. All ecosystems showed comparable number (12-14) of species in winter, but in the rainy season higher number of species (21) were recorded in the grassland ecosystem. The species composition of the grassland was entirely different from both agroecosystems (similarity <1%). Dryland and irrigated agroecosystems showed only 25% and 38% similarity with each other during winter and rainy cropping seasons, respectively. Occurrence of few grasses (e.g., Cynodon dactylon, Dichanthium annulatum and Sporobolus diander) in the agroecosystems depends on the propagules dispersed from the marginal grassland. The change from dryland to irrigated agroecosystem involved elimination of 4-5 species during both cropping seasons and simultaneous recruitment of 2 new species in winter and 6 species in rainy season. In both agroecosystems, forbs (C_ type) dominated over graminoids (C_ type) during winter season but the dominance was reversed during the warm, rainy season. During winter some forbs were abundant in both agroecosystems due to their tolerance to widely varying moisture conditions (e.g.,Chenopodium album), others were dominant in either drier soil conditions (e.g., Anagallis arvensis in dryland) or wet conditions (e.g., Melilotus indica and Phalaris minor in irrigated). Higher species diversity occurred in the grassland relative to both agroecosystems. The seasonal trends of species diversity and species evenness were broadly similar in both agroecosystems but irrigated agroecosystem exhibited relatively higher species diversity. The changes in species composition and species diversity in agroecosystems are mainly attributed to differences in water management. The water management in irrigated agroecosystem tends to reduce weed diversity but leads to the dominance of some potentially noxious weeds (e.g., Phalaris minor).

Restricted access
Community Ecology
Authors: F. Samu, F. Kádár, G. Ónodi, M. Kertész, A. Szirányi, É. Szita, K. Fetykó, D. Neidert, E. Botos, and V. Altbäcker

Recent environmental and land use changes have made wildfires more frequent in natural habitats of the Kiskunság Sand Ridge on the Hungarian Plain. In a study initiated 2.5 years after an extensive fire that destroyed half of the area of a sand grassland — juniper, poplar forest steppe habitat, we assessed the effects of fire on two generalist arthropod groups: spiders and carabid beetles, as well as on the vegetation. Utilizing the natural experiment situation, samples were taken by pitfalls and suction sampling during a 1.5 years period in four 1 ha blocks, two of which were on the burnt part of the habitat, and two in the unburnt control. At the time of the investigation, in the burnt area the vegetation in the grass layer showed a quick but not complete recovery, while the canopy layer of the juniper bushes burnt down with no sign of regeneration. Carabid beetles and spiders showed differences in recovery after fire. In the carabid assemblages of the burnt parts — compared to the unburnt control — there were over three times more beetles, out of which significantly more represented the macropterous life form and granivorous feeding strategy. There was a higher ratio of pioneer species and a simplified assemblage structure in the burnt area, which meant that the conservation value of the carabid assemblage became lower there. In contrast, for the spider assemblage quantitative changes in abundance and species numbers were not significant, and the differences in species composition did not lead to a decrease in conservation value. Spider species in the burnt plots could not be described as pioneer species, rather they had ecological characteristics that suited the changed vegetation structure. Comparing the two groups, to repopulate the burnt areas, dispersal abilities proved to be more limiting for carabids. However, in both groups a strong assemblage level adaptation could be observed to the postfire conditions. In spiders, species with a stratum preference for the grass layer prevailed, while in carabids individuals with granivore strategy gained dominance. Thus, despite the differences in their speed, basically both assemblages tracked vegetation changes. The effect of future fires will depend on their scale, as well as land-use practices, such as grazing, that interact with fire frequency and recovery. If extensive fires in the future permanently change the vegetation, then it would also lead to a fundamental change in the arthropod fauna.

Restricted access