|
| ||
|
|
||
Cattle Pasture (cattle + pasture)
Selected AbstractsCalifornia annual grass invaders: the drivers or passengers of change?JOURNAL OF ECOLOGY, Issue 5 2010Janneke HilleRisLambers Summary 1.,The dominance of invasive species is often assumed to reflect their competitive superiority over displaced native species. However, invasive species may be abundant because of their greater tolerance to anthropogenic impacts accompanying their introduction. Thus, invasive species can either be the drivers or passengers of change. 2.,We distinguish between these two possibilities in California grasslands currently dominated by Mediterranean annuals (exotics) and subjected to livestock grazing since European settlement. We focused on native annual grasses and forbs, an understudied species-rich component of the California flora, and Mediterranean annual grasses, currently dominant and among the first non-native plants introduced to the area. 3.,We established a field experiment with fenced and unfenced blocks in a cattle pasture. We measured concentrations of limiting resources (nitrogen, phosphorus, light and soil moisture) in monoculture plots as an index of competitive ability (i.e. R*). We then quantified grazing impacts on biomass and seed production in grazed vs. ungrazed monoculture plots. Finally, we measured biomass and seed production of each species competing in mixture plots, in the presence and absence of grazers. 4.,We found that native and exotic species did not differ in R* indices of competitive ability, i.e. concentrations of limiting resources in ungrazed native monoculture plots did not differ from concentrations in ungrazed exotic monoculture plots. By contrast, exotic annuals suffered less from grazing than native annuals, perhaps reflecting their longer evolutionary history with cattle grazing. Consistent with these results, native and exotic annuals were equally abundant in ungrazed mixtures, but exotic species overwhelmingly dominated grazed mixtures. 5.,Species able to draw down nitrogen and light to lower levels in monocultures (i.e. those with lower R* values) dominated biomass and seeds in mixed plots without grazers. However, R* did not predict the relative abundance of species in grazed plots. Moreover, the relative abundance of species in mixtures did not correlate with grazing impacts on their monocultures, implying that grazing alters inter-specific competitive dynamics. 6.,Synthesis. We demonstrate that the displacement of native annuals by Mediterranean annual grasses in California may largely have been driven by cattle grazing. [source] Discovery of a large clonal patch of a social amoeba: implications for social evolutionMOLECULAR ECOLOGY, Issue 6 2009OWEN M GILBERT Abstract Studies of genetic population structures of clonally reproducing macro-organisms have revealed large areas where only one clone is found. These areas, referred to as clonal patches, have not been shown to occur in free-living microbes until now. In free-living microbes, high genetic diversity at local scales is usually maintained by high rates of dispersal. We report, however, a highly dense, 12-m clonal patch of the social amoeba Dictyostelium discoideum in a cattle pasture located in a Texas Gulf Coast prairie. We confirm the presence of only one clone by the analysis of 65 samples and amplification of 10 polymorphic microsatellite loci. Samplings of additional cattle pastures nearby showed higher clonal diversity, but with a density of D. discoideum isolates lower than in the clonal patch. These findings show that high rates of microbial dispersal do not always produce genetic diversity at local scales, contrary to the findings of previous studies. The existence of clonal patches may be particularly important for microbial social evolution. [source] Effects of different secondary vegetation types on bat community composition in Central Amazonia, BrazilANIMAL CONSERVATION, Issue 2 2010P. E. D. Bobrowiec Abstract The process of secondary succession on degraded lands in the Amazon depends on their land-use histories. In this scenario, little is known about how animal communities respond to different types of secondary vegetation in the region. We examined the effects of abandoned cattle pasture, Vismia - and Cecropia -dominated regrowth on the abundance of bat species and community composition in the Central Amazon, Brazil, based on 11 netting sites and on landscape characteristics. We captured 1444 bats, representing 26 species and two families (Phyllostomidae and Mormoopidae). Among the six most-captured Phyllostomidae bats, Sturnira lilium and Sturnira tildae had significantly higher capture rates in abandoned pasture, while Rhinophylla pumilio predominated in both Vismia - and Cecropia -dominated regrowth. An hybrid multidimensional scaling ordination revealed significant differences in the bat community among the three types of secondary vegetation. Phyllostominae bats were more common and richer in the less-disturbed areas of Cecropia -dominated regrowth, while Stenodermatinae species were more captured in abandoned pastures. Our results suggest that the type of secondary vegetation, together with its land-use history, affects bat community composition in the Central Amazon. The Phyllostominae subfamily (gleaning animalivores) was habitat selective and disappeared from areas experiencing constant disturbances. On the other hand, Stenodermatinae frugivorous bats often used and foraged in altered areas. We suggest that secondary vegetations in more-advanced successional stages can be used to augment the total area protected by forest conservation units. [source] Key tree species for the golden-headed lion tamarin and implications for shade-cocoa management in southern Bahia, BrazilANIMAL CONSERVATION, Issue 1 2010L. C. Oliveira Abstract The golden-headed lion tamarin Leontopithecus chrysomelas occurs in the Atlantic forest of southern Bahia, Brazil, where shade-cocoa agroforestry (known as cabruca) predominates. The economic decline of the cocoa industry has caused many landowners to convert cabruca into cattle pasture or diversify their plantations with other crops. These and prior anthropogenic disturbances such as habitat fragmentation are threatening lion tamarin persistence. For some lion tamarin groups, cabruca comprises a large part of their home range. Considering these factors, the maintenance of the biological diversity in cabruca favorable to golden-headed lion tamarins is of considerable interest to their long-term survival. Here we identify plant species that provide food and sleeping sites for the lion tamarins and examine their occurrence in cabruca plantations, in order to investigate alternatives for conservation management practices that benefit both lion tamarins and cabruca. We determined the total number of trees and the frequency of individuals and species used for food and sleeping sites by lion tamarins in Una Biological Reserve, Bahia, from 1998 to 2006. We used this information to compare the richness and frequency of use across habitats (cabruca, mature and secondary) and to create a ranking index considering various components of a tree species' utility to the lion tamarins. Lion tamarins used 155 tree species, 93 for food and 93 for sleeping sites. Fifty-five species were ranked as ,Extremely Valuable,' eight as ,Valuable' and 92 as ,Of Interest.' Of 48 families, Myrtaceae and Sapotaceae were used the most. Cabruca contained fewer individual trees used by lion tamarins, but the highest frequency of use per tree compared with other habitats, indicating the large influence of single trees in these plantations. Using the key tree species identified in our study in the management of cabruca would be of considerable benefit to the long-term survival of lion tamarins [source] Spatial population structure in a patchily distributed beetleMOLECULAR ECOLOGY, Issue 4 2001Tomas Roslin Abstract The dynamics and evolution of populations will critically depend on their spatial structure. Hence, a recent emphasis on one particular type of structure , the metapopulation concept of Levins , can only be justified by empirical assessment of spatial population structures in a wide range of organisms. This paper focuses on Aphodius fossor, a dung beetle specialized on cattle pastures. An agricultural database was used to locate nearly 50 000 local populations of A. fossor in Finland. Several independent methods were then used to quantify key processes in this vast population system. Allozyme markers and mitochondrial DNA (mtDNA) sequences were applied to examine genetic differentiation of local populations and to derive indirect estimates of gene flow. These estimates were compared to values expected on the basis of direct observations of dispersing individuals and assessments of local effective population size. Molecular markers revealed striking genetic homogeneity in A. fossor. Differentiation was only evident in mtDNA haplotype frequencies between the isolated Åland islands and the Finnish mainland. Thus, indirect estimates of gene flow agreed with direct observations that local effective population size in A. fossor is large (hundreds of individuals), and that in each generation, a substantial fraction (approximately one-fifth) of the individuals move between populations. Large local population size, extreme haplotype diversity and a high regional incidence of A. fossor all testify against recurrent population turnover. Taken together, these results provide strong evidence that the whole mainland population of A. fossor is better described as one large ,patchy population', with substantial movement between relatively persistent local populations, than as a classical metapopulation. [source] Hurricane Disturbance Alters Secondary Forest Recovery in Puerto RicoBIOTROPICA, Issue 2 2010Dan F.B. Flynn ABSTRACT Land-use history and large-scale disturbances interact to shape secondary forest structure and composition. How introduced species respond to disturbances such as hurricanes in post-agriculture forest recovery is of particular interest. To examine the effects of hurricane disturbance and previous land use on forest dynamics and composition, we revisited 37 secondary forest stands in former cattle pastures across Puerto Rico representing a range of exposure to the winds of Hurricane Georges in 1998. Stands ranged from 21 to>80 yr since agricultural abandonment and were measured 9 yr posthurricane. Stem density decreased as stands aged, while basal area and species richness tended to increase. Hurricane disturbance exerted contrasting effects on stand structure, contingent on stand age. In older stands, the basal area of large trees fell, shifting to a stand structure characteristic of younger stands, while the basal area of large trees tended to rise in younger stands with increasing hurricane disturbance. These results demonstrate that large-scale natural disturbances can alter the successional trajectory of secondary forest stands recovering from human land use, but stand age, precipitation and soil series were better predictors of changes in stand structure across all study sites. Species composition changed substantially between census intervals, but neither age nor hurricane disturbance consistently predicted species composition change. However, exposure to hurricane winds tended to decrease the abundance of the introduced tree Spathodea campanulata, particularly in smaller size classes. In all sites the abundance of the introduced tree Syzygium jambos showed a declining trend, again most strongly in smaller size classes, suggesting natural thinning through succession. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] | ||||||||||