1,721,006 research outputs found
Endemic forest birds of the Taita Hills: using a model species to understand the effects of forest fragmentation on small populations
Full text linkDespite intense publicity, habitat loss still remains a serious threat to biodiversity. Forest destruction is its frontrunner, both in terms of physical habitat under threat and potential for biodiversity loss. In the fragmented landscape of the Taita Hills, SE Kenya, several bird species are facing the threat of extinction from forest loss. They are absent from many of the remnant forest patches and/or are showing negative effects with increasing disturbance. Using a relatively common forest-dependent bird species - the whitestarred robin Pogonocichla stellata - as a model, the current status of this ecosystem was examined, and future patterns predicted in view of the unrelenting destruction. As expected, the robin population in the largest and most intact fragment (c35 ha) was the healthiest, suggesting that this was indeed the best quality habitat patch: it had the highest population density, highest productivity (low nest predation and high juvenile to adult ratio) and lowest turnover rates. Effects of forest deterioration were evident from the fact that the medium-sized patch (c95 ha), which is undergoing severe degradation, was a worse habitat for the robin than the tiny patches (c2-8 ha): it had the lowest population density, lowest productivity (highest nest predation rates and lowest juvenile to adult ratio), and highest turnover rates. The explanation for this is twofold. Besides the smallest patches facing lower levels of habitat loss recently, they also had high levels of dispersal between them. They occasionally operated as a finegrained system with individuals moving between them in the space of a few days. In general, the robin metapopulation is demographically (rate of change, λ = 0.996) and genetically (at migration- and mutation-drift equilibrium) stable at present. The populations in the largest and smallest patches were potential sources providing emigrants that were possibly crucial in sustaining the population in the medium-sized patch (given its low productivity and high turnover rates). Overall, these findings underscore the importance of within-patch processes, both for ensuring persistence of subpopulations and providing dispersers, as well as between-patch processes (chiefly dispersal) for ensuring metapopulation persistence. Thus, by furnishing ample sample sizes that enabled work to be carried out in all fragments throughout this landscape, the model species approach was useful for identifying the need for a two-pronged conservation strategy. First, a need to focus within fragments to reduce habitat loss and degradation, and second, to address among fragment issues relating to land-use and maintaining a forested landscape, in order to enhance connectivity between patches. Finally, based on the mechanisms by which disturbance and fragmentation are affecting bird populations e.g. predator influxes from the surrounding matrix, conservation recommendations for the Taita Hills are offered
Habitat degradation relates to reduced immune function in nestlings, but not adults, of a tropical forest bird
Full text linkAbstract Human-induced habitat loss, fragmentation and degradation are among the leading causes of species decline worldwide. This is particularly true in tropical forests, where unique, often highly specialized fauna is under threat. By altering resource availability, anthropogenic habitat change can impose resource constraints on animals and may influence their allocation of resources to competing life history traits. In this study, we investigated whether nestlings and adults differently invest in self-maintenance depending on habitat degradation in the placid greenbul ( Phyllastrephus cabanisi placidus ), a cooperative breeder native to the cloud forests of Eastern Africa. We quantified investment in self-maintenance by measuring innate immune function using bacteria killing assays (BKAs) in adult breeders and their nestlings along a gradient of fragmented and degraded forests of the Kenyan Taita Hills. While innate immune function is an important defence against pathogens, resources needed to maintain it may come at a cost to other processes such as nestling development. We show that while forest degradation did not affect adult innate immune function, nestlings bear the cost of growing up in degraded habitats, as their ability to clear bacteria from blood plasma was lower in areas with degraded vegetation. These findings highlight the importance of studying the effects of habitat fragmentation and degradation in the tropics, where most of the global biodiversity occurs, and where long-lived species may respond differently from short-lived temperate ones, for example by prioritising self-preservation over reproduction
Metapopulation or source-sink system: does it matter? A brief overview, and an example from a highly fragmented Afrotropical forest
No full textAvian Frugivory and Seed Dispersal in Some of the Taita Hills Forests Fragments
No full textThis work was chiefly carried out in seven forest fragments in the Dabida massif of the Taita Hills-Ngangao, Chawia, Fururu, Ndiwenyi, Macha, Mwachora and Yale, between September 1997 and June 1998. Kasigau was also included for some analyses.The principal aim was to examine various aspects of the fleshy fruit-avian frugivore interface Transects were laid in all fragments and used for bird and fruit censuses, and for assessment of regeneration. Timed watches were used to describe frugivore assemblages at selected trees.
Data on fleshy fruits and avian frugivores were collected from transects in Dabida and grouped into sections (each comprising of 2~5 transects) for the analyses. Three rounds of data were collected in two distinct time periods - wet season (September to November) and dry season (January to March) In total, I identified 110 plant species (trees, shrubs and climbers) of which about 76% were fleshy fruit-producers. Overall tree diversity was lower in the smaller fragments, which were also the most disturbed.
Fruit density varied spatially and temporally, peaking in January in Ngangao and in October-November in Chawia and the smaller fragments Sections with the highest fruit densities fluctuated most I recorded 14 avian frugivores, of which five (Cabanis's and Stripe-cheeked Greenbuls, Hartlaub's Turaco, Taita Thrush and Taita White-eye) were relatively important in terms of density, distribution and frugivory levels. In general, frugivore densities were not linked to total fruit densities. During the period of lowest fruit abundance, but not at other times, significant explanatory variables for frugivore densities in a General Linear Model (GLM) included fragment size and tree diversity
(corrected for fragment size): the relationship was positive in both cases. Frugivore numbers did not appear to track fruit supplies; density fluctuations were more likely connected with seasonal breeding ehaviour, as the recorded densities of both frugivores and non-frugivores changed in a similar way, and showed declines during peaks in breeding activity.
Using Mantel statistics I examiried the frugivore assemblages of 58 individual trees belonging to 11 species growing in seven forest fragments-six in Dabida plus Kasigau Overall, there was little evidence r of specialized frugivorous interactions. Site and fruit size significantly affected similarity of frugivore assemblages among conspecific and
heterospecific tree species, respectively. Effect of location of tree could be attributed to forest fragments of different sizes varying in densities and composition of focal fruiting trees, and in the fruiting phenologies of these trees.
Consequently, my findings indicate that at least one important processes of seed dispersal-fruit selection-may have been affected by habitat fragmentation. Lastly, I looked at the spatial patterns of young and adult individuals of mainly bird-dispersed plants (five tree and one climber species). Regenerating individuals (both of the trees and climber) occurred more on species which were also fleshy fruiting, than
expected from their relative densities in the habitat This could be attributed, at least partly, to the foraging patterns of the avian frugivores, which suggests some potential to 'shape' their habitats. Secondly, I found little congruence between the spatial patterns of young and regenerating individuals of the five tree species, which was consistent for all sections This could imply that the avian frugivores were unlikely to be highly efficient seed dispersers for these trees; and that they had fairly comparable dispersal efficiencies Lastly, pioneer species regenerated better in disturbed areas, whereas the non-pioneer
species, since they do not require large gaps for germination and establishment, were found to regenerate better in larger, less disturbed fragments
Using scientific evidence to guide the conservation of a highly fragmented and threatened Afrotropical forest
No full textFragmentation of forests adversely affects forest-dependent biota, and conservation biologists strive to develop a good understanding of how species respond to changes associated with habitat attrition in order to establish the best conservation strategies. The spatial structure of populations persisting in fragmented landscapes governs their response to habitat fragmentation, and hence dictates the remedial actions that will be most effective for species and habitat conservation. The Taita Hills forests of Kenya are an example of a highly fragmented Afrotropical forest ecosystem embedded in a human-dominated landscape. The spatial structure of the white-starred robin Pogonocichla stellata populations living in indigenous forests across this landscape was examined. Due to its forest dependence and widespread occurrence, the robin was used as a model species to help formulate general conservation guidelines for forest-dependent species and their habitats within this landscape. Results from demographic, genetic and behavioural work point to a mixed spatial structure with elements of patchy population dynamics on a fine scale, and a core-satellite or source-pseudo-sink system on a broader scale. In particular, the findings underscore (1) the importance of dispersal, (2) the importance of small patches, (3) the importance of the largest patch, and (4) the processes underlying problems associated with forest disturbance. We examine the conservation implications of this information, and report on activities already initiated or planned, in line with these findings, for the Taita Hills
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Avian diversity in forest gaps of Kibale Forest National Park, Uganda
No full textVolume: 28Start Page: 1End Page: 1
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Avifauna of the Brachylaena woodlands in the Usambara lowlands, Tanzania
No full textVolume: 5Start Page: 13End Page: 1
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