No description available.

abstract: Habitat fragmentation, the loss of habitat in the landscape and spatial isolation of remaining habitat patches, has long been considered a serious threat to biodiversity. However, the study of habitat fragmentation is fraught with definitional and conceptual challenges. Specifically, a multi-scale perspective is needed to address apparent disagreements between landscape- and patch-based studies that have caused significant uncertainty concerning fragmentation’s effects on biological communities. Here I tested the hypothesis that habitat fragmentation alters biological communities by creating hierarchically nested selective pressures across plot-, patch-, and landscape-scales using woody plant community datasets from Thousand Island Lake, China. In this archipelago edge-effects had little impact on species-diversity. However, the amount of habitat in the surrounding landscape had a positive effect on species richness at the patch-scale and sets of small islands accumulated species faster than sets of large islands of equal total size at the landscape-scale. In contrast, at the functional-level edge-effects decreased the proportion of shade-tolerant trees, island-effects increased the proportion of shade- intolerant trees, and these two processes interacted to alter the functional composition of the regional pool when the total amount of habitat in the landscape was low. By observing interdependent fragmentation-mediated effects at each scale, I found support for the hypothesis that habitat fragmentation’s effects are hierarchically structured. / Dissertation/Thesis / Doctoral Dissertation Biology 2018

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Habitat fragmentation through the loss and modification of natural ecosystems poses a serious threat to biodiversity globally. Mechanisms and ecological implications of fragmentation have been extensively studied, yet new and meaningful insights continue to be produced. The highly diverse and ecologically complex fynbos shrubland communities that occur in the Cape Floristic Region of South Africa are amongst the most threatened by habitat fragmentation by urban, agricultural and silvicultural land uses and to the spread of invasive alien plants. Fynbos vegetation communities are fire-adapted and exploit the post-fire regeneration niche. Natural stochasticity in the fire regime means that these communities are temporally unstable; a factor that allows for the coexistence of such extreme diversity. Few studies have attempted to assess the influence of habitat fragmentation on this stochasticity, or to investigate the response of biological communities to the conditions that result. It is unknown whether this temporal instability will lead to delayed extinctions in fragmented communities, thus generating extinction debt. South Outeniqua Sandstone Fynbos occurs as a unique landscape mosaic of both insular and extensive habitats, suited to study through an island biogeography framework. Vegetation community stability was assessed through the comparison of historic and recent data sets. The responses of local vegetation and avifaunal communities to habitat fragmentation were assessed and compared on the basis of their differing motility. The unique habitat configurations also allowed for the investigation of extinction debt in the local communities and provided an opportunity to assess the influence of the surrounding matrix on species persistence and on connectivity in the artificial fragments. Data were analysed through simple regression analyses, modified Chi-squared tests and through ordination analyses. Ultimately the value of the artificial habitat fragments for the conservation of biological communities was assessed. Stability was observed in the vegetation species-area relationship for the natural islands and the mainland sites over twenty-two years. Smaller islands were found to receive fewer fires than large islands and the mainland. This consistently over-extended fire-return interval reduces the stochasticity of the local fire regime causing stable yet depauperate vegetation communities to result. Vegetation communities in the artificial fragments were found to hold area-related extinction debt, possibly due to the relatively long-term demographic turnover that typically occurs in fynbos. Avifaunal communities varied in their response to fragmentation relative to the vegetation. Birds – being motile – were found to be unaffected by isolation distance or surrounding matrix type – their response due more to changes experienced in the vegetation community than to geographic constraints. Fynbos-typical birds responded to the post-fire age of vegetation. Frugivorous birds and the matrix-habitat edge were identified as sources of alien and non-fynbos plant species that colonise the artificial fragments, potentially reducing the quality of these habitats for avifauna. Fragmented communities of South Outeniqua Sandstone Fynbos have the potential to function as biological reserves. This potential can be realised through the implementation of a fire regime that acknowledges the stochasticity required by the vegetation, the frequency required by the vegetation and the avifauna, and the practicality required by surrounding anthropogenic land-uses. / AFRIKAANSE OPSOMMING: Habitat-fragmentering, deur die verlies en verandering van natuurlike ekosisteme, hou 'n ernstige bedreiging in vir biodiversiteit wêreldwyd. Meganismes en ekologiese implikasies van die fragmentering is al breedvoerig bestudeer, maar nuwe en betekenisvolle insigte word voortaan vervaardig. Die hoogs diverse en ekologies komplekse fynbos-struikveld gemeenskappe wat in die Kaapse Floristiese Streek van Suid-Afrika voorkom, word meeste bedreig deur habitat-fragmentering deur verstedeliking, landbou en houtteeltkundige grondgebruike en die verspreiding van indringerplante. Fynbos gemeenskappe is aangepas tot vuur en die uitbuiting van post- vuur herlewing nis. Natuurlike stogastisiteit in die vuur-bedeling beteken dat hierdie gemeenskappe tydelik onstabiel word, 'n faktor wat die mede-bestaan van uiterste diversiteit moontlik maak. Min studies het al die invloed van habitat-fragmentering op hierdie stogastisiteit ondersoek, of die reaksie van biologiese-gemeenskappe tot die voortspruitende omstandighede. Dit is onbekend of die tydelike onstabiliteit sal lei tot vertraagde uitsterwing in gefragmenteerde gemeenskappe, dus genereer uitsterwings-skuld. Suid Outeniqua Sandsteen Fynbos kom as 'n unieke landskap mosaïek van beide die eilande en uitgebreide habitatte voor, geskik om deur 'n eiland biogeografie raamwerk bestudeer te word. Plant-gemeenskappe se stabiliteit is bestudeer deur die vergelyking van historiese en onlangse data stelle. Die reaksies van die plaaslike plantegroei en voëllewe gemeenskappe tot hul habitat is bestudeer en vergelyk op grond van hul verskillende beweeglikheid. Die unieke habitat konfigurasies het ook toegelaat vir die ondersoek van uitsterwings-skuld in die plaaslike gemeenskappe en 'n geleentheid gebied om die invloed van die omliggende habitat-matriks op spesies volharding en op konneksie in die kunsmatige fragmente te bepaal. Die data is ontleed deur middel van eenvoudige regressie analises, aangepasde Chi -kwadraat toetse en deur koördinerings ontledings. Ten einde die waarde van die kunsmatige habitat fragmente vir die bewaring van biologiese gemeenskappe te bepaal. Stabiliteit in die plantspesies-area verhouding vir die natuurlike eilande en die vasteland van webwerwe oor twee en twintig jaar was waargeneem. Kleiner eilande het minder brande aangeneem as groot eilande en die vasteland. Hierdie herhaalde oor-uitbrei over-extended vuur-interval het die stogastisiteit verminder van die plaaslike vuur-bedeling wat stabiele tog spesie-arme plantegroei gemeenskappe veroorsaak het. Plantegroei gemeenskappe in die kunsmatige fragmente is bevind om spesie- area -verhouding uitsterwings-skuld te bevat, moontlik as gevolg van die relatiewe lang termyn demografiese omset wat tipies voorkom in fynbos. Voëllewe gemeenskappe het gewissel in hul reaksie tot die fragmentering relatief tot die plantegroei. Voëls – weens hul beweeglikheid – blyk om nie beinvloed te word deur isolasie afstand of omliggende habitat-matriks tipe nie - hul reaksie blyk meer asgevolg van veranderinge wat ervaar word in die plantegroei gemeenskap as geografiese beperkinge. Fynbos-tipiese voëls reageer op die post- vuur ouderdom van plantegroei. Vrugte-etende voëls en die habitat-matriks rand is geïdentifiseer as bronne van uitheemse en nie-fynbos plantspesies wat die kunsmatige fragmente koloniseer, wat potensieel die kwaliteit van hierdie habitatte vir voëls verminder. Gefragmenteerde gemeenskappe van Suid Outeniqua Sandsteen Fynbos het die potensiaal om as biologiese reserwes te funksioneer. Hierdie potensiaal kan verwesenlik word deur die implementering van 'n vuur-bedeling wat erkenning verleen aan die stogastiesiteit vereis deur die plantegroei, die frekwensie wat deur die plantegroei en die voëllewe vereis word , en die praktiese vereistes van die omliggende menslike grondgebruike.

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Habitat fragmentation is often regarded as a biodiversity threat associated with habitat degradation; however, research has also revealed beneficial effects on biodiversity as well, depending on the ecosystem and species community. This study examined the biodiversity of small nekton residing in seagrass meadows characterized by three levels of habitat fragmentation, and as a habitat gradient comprised of measures such as habitat amount, connectivity, patch shape, and proximity. Landscapes were mapped using recent advances in GPS and GIS technology, and analyzed using established methods from research in terrestrial ecosystems. Species richness was not significantly different as a function of fragmentation regardless of season, suggesting that the amount of habitat and configuration of several patches in fragmented habitats is sufficient to support comparable numbers of species in several patches compared to communities in large, continuous seagrass meadows. Species evenness declined significantly in fragmented habitats versus continuous ones in both seasons. Within fragmented landscapes, evenness progressively declined as habitat amount and connectivity decreased and patch isolation and density increased, suggesting that changes in landscape qualities can differentially impact processes supporting metapopulations such as dispersal and reproduction in certain species, thereby influencing community structure. Analyses that included measures of habitat connectivity, proximity, and patch density in addition to habitat amount accounted for more variability in species evenness than those just containing percent cover, and showed that fragmentation’s impacts can differ geographically. These data suggest that community resilience to fragmentation can differ between similar animal communities residing in separate locations, and that landscape configuration plays an important role in determining how communities respond to fragmentation after a threshold of change in habitat amount has been exceeded. / text

Northern bobwhite (Colinus virginianus) and swamp rabbits (Sylvilagus aquaticus) are species both strongly influenced by habitat loss and fragmentation in agricultural landscapes. Population declines for the bobwhite and the paucity of information regarding swamp rabbit prevalence add uncertainty to their potential for persistence in Illinois. Research has indicated that these 2 species rarely disperse long distances. In a metapopulation context, such limitations ultimately dictate species' ability to colonize habitat, thereby affecting their persistence. Since gene flow is one of the consequences of dispersal, I employed genetic investigations of the landscape features that affect gene flow, called landscape genetics, to aid the understanding of factors influencing the persistence of the northern bobwhite and swamp rabbit in an agricultural landscape. Tissue samples were collected from hunter harvested bobwhite in central and southern Illinois during 2007-2008. Tissue from trapped swamp rabbits and fecal pellets from swamp rabbit habitat were collected during 2004-2011 in the southernmost counties of Illinois. Microsatellite genetic markers were analyzed for each species. Bayesian clustering methods were used to find interbreeding groups. Levels of gene flow were assessed with F statistics. Correlations between individual genetic distances and landscape features provided an assessment of geographical attributes affecting gene flow. Northern bobwhite expressed less genetic structure among the southern and central counties of Illinois than expected from their sedentary reputation. Genetic differentiation among pre-defined subpopulations was low (FST <0.05) but significant. Genetic clusters were not tightly linked to geography. Individual-based analysis indicated that distance impacted gene flow more than the distribution of suitable habitat or highway barriers. Additionally, the distribution of suitable habitat on the landscape had a negative affect on gene flow indicating bobwhite may disperse through unsuitable habitat more readily than through suitable habitat. These results suggest that greater area of suitable habitat and improvement of existing habitat may be more beneficial to bobwhite than its arrangement or position on the landscape. Significant genetic structure was observed in swamp rabbits in the Cache River watershed of southernmost Illinois. Bayesian clustering indicated 4 distinct genetic groups inhabited the study area. Such structuring suggests swamp rabbits in the northernmost part of their range experience low connectivity among habitat patches and are consequently at risk for extinction in Illinois. Gene flow of swamp rabbits was tied to watercourses indicating their affinity for a water source impacts their dispersal tendencies. Gene flow was negatively impacted by highway barriers, which may interrupt swamp rabbit dispersal due to their avoidance of roads or land cover associated with roads. Alterations to swamp rabbit habitat that leads to loss, increased fragmentation, or increased road density may have severe negative impacts and should be avoided. Habitat improvement focused closer to watercourses may provide a greater benefit for swamp rabbits.

No description available.

An investigation into the effects of deforestation and habitat fragmentation on a central Amazonian frog community was carried out on the Biological Dynamics of Forest Fragments Project, (BDFFP) based in Manaus, Amazonas, Brazil. Three aspects of deforestation were investigated: the effects of fragmentation and reserve size, the influence of matrix habitat and the effects offorest edge on frogs in 10- hectare isolates. Very few frogs species were lost from fragments (regardless of size) following fragmentation and isolation for 7-10 years. Instead, frog species richness increased, with an average increase in 10 species per fragment. The increase in species was brought about by an increase in matrix associated species, some of which were present in the absence of their preferred breeding habitat. Different frog species had varied responses to fragmentation. The abundance of Eleutherodactylus fenestratus, a terrestrial breeder, increased significantly as fragment size decreased, and its abundance was significantly higher in both large and small fragments than in continuous forest. Colostethus stepheni, a semi-terrestrial breeder, was less abundant in fragments than continuous forest. Finally, Eleutherodactylus zimmermanae and Osteocephalus sp.A did not differ significantly in abundance among fragments, or between fragments and continuous forest. Multiple regression analysis indicated that variation in litter depth and canopy cover may explain the observed increase in E. fenestratus abundance in small fragments. Breeding success of pool breeders attracted to artificial pools was variable, but there was no evidence of reduced breeding success in fragments relative to primary forest. Overall, fragmentation appeared to affect the frog community less severely than other taxonomic groups. Species richness in tropical forest remnants showed a tendency to increase as a result of fragmentation, and only one of four species exhibited lowered abundance in fragments. The effects of fragmentation and subsequent small isolated populations of frog species in fragments was alleviated somewhat by the ability of central Amazonian frogs to utilise matrix habitat. Litter frogs, wallow breeders and upland forest pool breeders all displayed an ability to permeate, and in most cases become residents of matrix habitat. Both matrix with a history of cut and burn and matrix which was only cut supported a similar frog community. Thus, for central Amazonian frogs isolates were not truly isolated due to the ability of frogs to utilise matrix habitat. Litter frogs in 10- hectare isolates displayed an independence from edge related abiotic and biotic gradients. This independence was true for frog species richness, abundance and composition. Consequently, forest fragments are in effect larger for frogs than for other taxa who are constrained by edge effects to exist only within the core of large fragments. Colostethus stepheni was one species found to be negatively affected by habitat fragmentation. Abundance of Colostethus stepheni was significantly lower in fragments and matrix habitat compared to primary continuous forest. This species was also found to be sensitive to edge, with higher abundances recorded as distance from the edge increased. The community level approach adopted in this study, as opposed to intensive investigation of single species, may well have overlooked other' sensitive' species which show more subtle responses to habitat fragmentation than that of Colostethus stepheni. The ability to use matrix and the relative independence from edge related phenomena accounts for the resilience of central Amazonian frogs in a disturbed and fragmented landscape. However, with respect to matrix habitat, forest surveyed in this study has not been repeatedly cut or cut and burnt (with the exception of pasture-land where the frog community is depauperate). In other areas of the Amazon, away from the experimental plots of the BDFFP, matrix habitat is destroyed more frequently. More work is needed to determine the ability of central Amazonian frogs to utilise matrix habitat which is disturbed more frequently.

Fatores biogeográficos, em particular a posição da população em relação à sua área de distribuição geográfica, podem mediar variações interpopulacionais da resposta das espécies à fragmentação do habitat. O presente estudo teve como objetivo verificar se a posição biogeográfica das populações pode predizer a sensibilidade das espécies de aves à distribuição espacial do seu habitat, medida pela cobertura e configuração dos remanescentes florestais em paisagens fragmentadas. Considerando 21 espécies presentes em pelo menos 30 fragmentos, estabelecemos modelos de regressão relacionando a abundância destas espécies com a cobertura e configuração dos remanescentes, e ainda com a posição biogeográfica das populações. A variável de posição biogeográfica foi obtida através de modelos de distribuição das espécies, utilizando o algoritmo de máxima entropia (Maxent). Utilizamos o Critério de Informação de Akaike (AIC) para comparar os modelos e verificar a importância relativa de cada variável. Grande parte das espécies (n = 10) apresentou um padrão de resposta semelhante, que é o de serem influenciadas tanto por variáveis de configuração da paisagem, quanto pela posição biogeográfica em que se encontram as populações. Outras seis espécies foram influenciadas somente por características da paisagem, enquanto duas foram influenciadas somente pela posição biogeográfica das populações. Houve ainda três espécies que não mostraram sofrer influência de nenhuma das variáveis utilizadas. Não foram verificadas características biológicas das espécies que estivessem relacionadas com esses grupos de respostas das espécies. De maneira geral, o presente estudo mostrou que a posição biogeográfica das populações, assim como os parâmetros de estrutura da paisagem, são fatores importantes na determinação da abundância das populações da maioria das espécies de aves em paisagens fragmentadas. Tais resultados têm implicações para o próprio entendimento da persistência de populações de aves em paisagens fragmentadas, assim como para o direcionamento de esforços voltados para planos de conservação em escalas regionais. / Species distribution models (SDM) is a quite new technique that has been used in many fields of natural sciences. Nevertheless, as problem inherent of a new technique, there is still a lot of questions about the most appropriated manner of its use and application. As the SDM consists a powerful tool with high potential to be used use in many fields of research, it is extremely useful that tests are carried out, to improve and refine this technique. To help in the development of the SDM, this study consist a methodological test that aims to compare the performance of different algorithms used in SDM. We used points of occurrence of 21 bird species along an area of nearly 1,200,000 km2 in southeastern Brazil. The data were obtained through a rough bibliographic revision. Environmental layers used in the modeling procedure consisted of 19 bioclimatic variables, besides altitude and slope of the terrain. The algorithms used were Maxent, GARP and SVM. As a performance parameter of the algorithms we used the area under de ROC curve (AUC), generated with points of occurrence independent of the ones used for the modeling procedure. Based on the AUC values, we observed a higher prevision capacity of the models generated with Maxent, followed by the ones generated with SVM, and at least, the ones generated with GARP. The pattern of the probability distributions of the models generated with Maxent and SVM had a higher biological meaning, besides agreeing more with the species real area of occurrence. As conclusion of this study we consider that Maxent is the most appropriate algorithm to be used in species distribution models, that are made under the same conditions of the ones used in the present study. Biogeographical factors, specially the location of populations in relation to the occurrence area of the species, could mediate interpopulational variations in species response to habitat fragmentation. The present study aimed to verify if the biogeographical position of populations can predict bird species sensitivity to habitat spatial distribution, measured as the forest cover and configuration in fragmented landscapes. Considering 21 species present in at least 30 fragments, we established regression models relating the abundance of the species with patch cover and configuration of the patches, and with the population biogeographical position. This position was obtained through species distribution models, with the maximum entropy algorithm (Maxent). We used the Akaike Information Criteria (AIC) to compare the models and verify the relative importance of each variable. Most of the species (n= 10) presented a similar response pattern, being influenced by landscape configuration and also by biogeographical position parameter. Six other species were influenced only by landscape structure, while two species were influenced only by biogeographical position. There were also three other species that were not influenced by any of the used variables. The response pattern to the independent variables seems to be independent of the biological characteristic of the species. The present study showed that the biogeographical position of the populations could be, with the landscape structure, an important factor to determine the abundance of major part of bird species in a fragmented landscape. Such results have implications on the comprehension of bird species persistence in fragmented landscapes, as well to driven effort for conservation plans in regional scales.

<i>Festuca hallii</i> [(Vasey) Piper] (plains rough fescue) is a dominant native grass species in the Fescue Prairie region of North America that has undergone dramatic range reduction in the past century. This research is undertaken to address the related issues associated with the effectiveness of sampling in capturing genetic diversity, the influence of habitat fragmentation on genetic variation, the geographic variation of seed germination characteristics, and the comparative genetic variation of differential germination. It was found that the tiller samples revealed slightly larger among-population variation than the seed samples. The fescue plant was genetically diverse, as revealed by the proportion of polymorphic bands, the mean band frequency, and the within-population variation. The genetic variation was not highly differentiated with only 6.5% of the total AFLP variation residing among populations. Mantel test revealed a significant correlation between genetic and geographic distances and a spatial autocorrelation up to 60 km among populations was detected. Base temperatures (<i>T_b</i>, minimal or base temperature permitting germination) of the 15 populations fell into a narrow range within 2.2°C with an average of 1.1°C. High final germination percentage was reached at a wide temperature range from 5 to 20°C with the highest germination percentage at 10°C. Germination rate index increased with increasing temperature from 5 to 20°C. <i>T_b</i> was positively correlated with latitude and negatively with longitude and the thermal time requirement for 50% germination was negatively correlated with latitude. The AFLP variation and germination responses were significantly associated with environmental attributes related to moisture, indicating local adaptation. However, the AFLP variation and germination was not significantly associated with the estimated population size and geographic distance to the nearest neighbor, suggesting that fragmentation has not generated considerable genetic and germination impact on the fescue populations. Marked differences in estimates of mean band frequency were observed for various groups of germinating seeds under different test temperatures. Comparisons of AFLP variation among 27 groups of seeds representing population, germination timing and test temperature indicates seed genotypes respond slightly differently to environmental variation, resulting in significant but small impact of germination timing and temperature on the genetic diversity of populations. These findings are significant not only for understanding and predicting the ecological adaptation of the species, but also for formulating effective restoration strategies for remnant populations.