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Luc Lens - One of the best experts on this subject based on the ideXlab platform.
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effects of matrix composition and configuration on Forest bird movements in a fragmented afromontane biodiversity hot spot
Animal Conservation, 2012Co-Authors: Job Aben, Luc Lens, Petri Pellikka, Mika Siljander, Frank Adriaensen, Koen W Thijs, Erik MatthysenAbstract:Persistence of Forest-dependent species in fragmented landscapes strongly relies on sufficient dispersal between patches, making it important to understand how animal movements are affected by the intervening matrix. Movements can be influenced through selection or avoidance of land cover based on their perceived suitability for foraging or providing cover. The composition and configuration of the matrix will, therefore, most likely be an important factor to consider when estimating connectivity between patches. To address this, we performed translocation experiments to understand how Forest birds used different land cover types in a fine-grained matrix of a fragmented Afromontane biodiversity hotspot (Taita Hills, Kenya). Our results revealed that use of land cover types for both the Forest specialist Cabanis’s greenbul Phyllastrephus cabanisi and for the Forest generalist white-starred robin Pogonocichla stellata was disproportional to their availability. However, this effect was influenced by matrix configuration; in patchy matrices, land cover selection was more pronounced compared with more uniform matrices, especially for the Forest specialist. At the scale of movement steps, risk avoidance seemed to be a strong factor in the route decisions for both species. Observed steps contained on average lower proportions of open land cover and did less frequently intersect built-up areas than expected. P. stellata did not differentiate between the alternative land cover types, whereas P. cabanisi preferred steps that contained more Indigenous Forest. The observed negative relationship between degree of Forest dependency and matrix permeability implies that for members of the Taita bird community, which are even more dependent on intact Forest habitat (i.e. the critically endangered Taita thrush Turdus helleri), current permeability of the matrix may be even lower. Matrix restoration to improve connectivity may, therefore, be a crucial instrument for the long-term survival of Forest-dependent species in these fragmented Afromontane landscapes.
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complementary seed dispersal by three avian frugivores in a fragmented afromontane Forest
Journal of Vegetation Science, 2009Co-Authors: Valerie Lehouck, Toon Spanhove, Sebastien Demeter, Nikee E Groot, Luc LensAbstract:Questions To what extent does species-specific variation in gut passage time (GPT), habitat use and mobility of three key avian frugivores synergistically affect the distribution of Xymalos monospora seeds within and among isolated Forest fragments? Location Three fragments of a severely fragmented cloud Forest, Taita Hills, southeast Kenya. Methods We experimentally determined GPTs of X. monospora seeds and recorded movements and habitat use by Turdus helleri, Andropadus milanjensis and Tauraco hartlaubi through radiotelemetry, and combined these data to generate species-specific seed dispersal patterns. Results Differences in mobility and habitat use among the three frugivores caused significant complementarity in seed dispersal, despite the fact that gut transit times were highly comparable. While the most sedentary and Forest-dependent species mainly led to short-distance dispersal away from parent trees, two more mobile species dispersed seeds further away from the source trees, both within Indigenous Forest patches and towards exotic plantations and isolated fruiting trees in the landscape matrix. A. milanjensis inhabiting a very small Forest fragment spent significantly more time in the landscape matrix than conspecifics residing in the two larger fragments. Conclusions By varying distances over which seeds are carried away from parent trees and the habitat types in which they are ultimately deposited, avian frugivores affect the spatial distribution of seeds and early plant recruits in a distinct and complementary manner. Because landscape properties are expected to lead to different constraints on avian mobility for habitat specialists and for generalists, ecosystem processes such as avian seed dispersal are shaped by complex interactions between disperser behaviour and the environment.
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does landscape structure affect resource tracking by avian frugivores in a fragmented afrotropical Forest
Ecography, 2009Co-Authors: Valerie Lehouck, Toon Spanhove, Carl Vangestel, Norbert J Cordeiro, Luc LensAbstract:Frugivorous species heavily depend on patchy food resources and are believed to track these in space and time, thereby providing an important seed dispersal function that might be critical toward the regeneration of fruiting plants. However, isolation of suitable food patches due to habitat fragmentation or changes in landscape connectivity may hamper food tracking behaviour and adversely affect populations of both frugivores (through starvation) and food plants (through interruption of seed dispersal). We here test whether density fluctuations in four frugivorous Afrotropical bird species were larger and/or matched fluctuations in ripe fruit densities better in study plots embedded in large tracts of Indigenous Forest than in equally-sized plots embedded in cultivated lands. We compared these results with those of four non-frugivorous species (out-group) which were not expected to track fruit resources. Whereas densities of both frugivores and fruit crops strongly fluctuated in space and time, these fluctuations were not synchronised, nor did the level of synchrony differ in relation to matrix type. For some but not all bird species, lower densities and smaller temporal fluctuations in Forest plots surrounded by cultivation may reflect decreased mobility. The observed fluctuations in bird densities most likely reflect exchange with the surrounding landscape matrix, suggesting that small pockets of fruiting trees in farmland may comprise critical food resources for frugivores inhabiting highly fragmented landscapes, apart from increasing connectivity for both bird and seed dispersal.
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airborne remote sensing of spatiotemporal change 1955 2004 in Indigenous and exotic Forest cover in the taita hills kenya
International Journal of Applied Earth Observation and Geoinformation, 2009Co-Authors: Petri Pellikka, Milla Lotjonen, Mika Siljander, Luc LensAbstract:We studied changes in area and species composition of six Indigenous Forest fragments in the Taita Hills, Kenya using 1955 and 1995 aerial photography with 2004 airborne digital camera mosaics. The study area is part of Eastern Arc Mountains, a global biodiversity hot spot that boasts an outstanding diversity of flora and fauna and a high level of endemism. While a total of 260 ha (50%) of Indigenous tropical cloud Forest was lost to agriculture and bushland between 1955 and 2004, large-scale planting of exotic pines, eucalyptus, grevillea, black wattle and cypress on barren land during the same period resulted in a balanced total Forest area. In the Taita Hills, like in other Afrotropical Forests, Indigenous Forest loss may adversely affect ecosystem services.
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fluctuating asymmetry increases with habitat disturbance in seven bird species of a fragmented afrotropical Forest
Proceedings of The Royal Society B: Biological Sciences, 1999Co-Authors: Luc Lens, S Van Dongen, Christine M Wilder, Thomas M Brooks, Erik MatthysenAbstract:We studied fluctuating asymmetry (FA) in the tarsus length of seven Forest-restricted bird species, two of which are globally critically endangered, in three Indigenous Forest remnants of a recently fragmented, afrotropical biodiversity hot spot. Based on mixed regression analysis and an extension of Levene's test, individuals from the most degraded fragment showed four- to sevenfold higher asymmetry levels compared to those from the least degraded one, with intermediate levels in the moderately disturbed fragment. When comparing contemporary FA levels with measurements of museum specimens collected 50 years ago, we found highly significant increases in asymmetry in the most degraded fragment but no differences in the least degraded one. These strikingly parallel spatial and temporal patterns across species confirm that repeated measurements of FA can provide a sensitive early warning system for monitoring stress effects in highly threatened ecosystems.
Harriet A C Eeley - One of the best experts on this subject based on the ideXlab platform.
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Priority areas for the conservation of subtropical Indigenous Forest in southern Africa: a case study from KwaZulu-Natal
Biodiversity & Conservation, 2001Co-Authors: Harriet A C Eeley, Michael J Lawes, Belinda ReyersAbstract:Southern Africa's subtropical Forest biome, though small and highly fragmented, supports much of the region's biodiversity. With limited resources available for conservation and the exploitative use of Forest escalating, identifying a network of priority Forest reserves is important. We examine the distribution of Forest birds, butterflies and mammals in KwaZulu-Natal, South Africa. Using an iterative algorithm we explore the efficiency of existing protected areas, species richness and rarity hotspots, prime Forest sites (selected by Forest area) and complementary networks as alternative approaches to priority reserve selection, as well as the potential use of ‘indicator’ taxa. Existing protected areas represent 98% of species but are relatively inefficient in terms of area. Alternative selection criteria represent a high proportion of species (86–92%) and provide efficient bases for developing fully representative reserve networks. All species are represented within a network of 22 complementary quarter degree cells. This network includes several larger Forests and existing protected areas and is recommended for priority conservation. Complementary networks identified separately for birds, butterflies and mammals overlap little, but each represents a high proportion of the remaining taxa, supporting their potential as representative 'indicator' taxa. The evolutionary history of the three main Forest types in KwaZulu-Natal explains observed spatial patterns of alternative reserve networks. Priority areas are concentrated in scarp and coastal Forest belts, regions of comparatively recent evolutionary activity with high species richness. Afromontane Forest is older and less diverse, but its inclusion in any reserve network is necessary for the full representation of Forest diversity.
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the influence of climate change on the distribution of Indigenous Forest in kwazulu natal south africa
Journal of Biogeography, 1999Co-Authors: Harriet A C Eeley, Michael J Lawes, S E PiperAbstract:Aims (1) To define the physical correlates of Indigenous Forest in KwaZulu-Natal province and develop a model, based on climatic parameters, to predict the potential distribution of Forest subtypes in the province. (2) To explore the impact of palaeoclimatic change on Forest distribution, providing an insight into the regional-scale/historical forces shaping the pattern and composition of present-day Forest communities. (3) To investigate potential future shifts in Forest distribution associated with projected climate change.
Erik Matthysen - One of the best experts on this subject based on the ideXlab platform.
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effects of matrix composition and configuration on Forest bird movements in a fragmented afromontane biodiversity hot spot
Animal Conservation, 2012Co-Authors: Job Aben, Luc Lens, Petri Pellikka, Mika Siljander, Frank Adriaensen, Koen W Thijs, Erik MatthysenAbstract:Persistence of Forest-dependent species in fragmented landscapes strongly relies on sufficient dispersal between patches, making it important to understand how animal movements are affected by the intervening matrix. Movements can be influenced through selection or avoidance of land cover based on their perceived suitability for foraging or providing cover. The composition and configuration of the matrix will, therefore, most likely be an important factor to consider when estimating connectivity between patches. To address this, we performed translocation experiments to understand how Forest birds used different land cover types in a fine-grained matrix of a fragmented Afromontane biodiversity hotspot (Taita Hills, Kenya). Our results revealed that use of land cover types for both the Forest specialist Cabanis’s greenbul Phyllastrephus cabanisi and for the Forest generalist white-starred robin Pogonocichla stellata was disproportional to their availability. However, this effect was influenced by matrix configuration; in patchy matrices, land cover selection was more pronounced compared with more uniform matrices, especially for the Forest specialist. At the scale of movement steps, risk avoidance seemed to be a strong factor in the route decisions for both species. Observed steps contained on average lower proportions of open land cover and did less frequently intersect built-up areas than expected. P. stellata did not differentiate between the alternative land cover types, whereas P. cabanisi preferred steps that contained more Indigenous Forest. The observed negative relationship between degree of Forest dependency and matrix permeability implies that for members of the Taita bird community, which are even more dependent on intact Forest habitat (i.e. the critically endangered Taita thrush Turdus helleri), current permeability of the matrix may be even lower. Matrix restoration to improve connectivity may, therefore, be a crucial instrument for the long-term survival of Forest-dependent species in these fragmented Afromontane landscapes.
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fluctuating asymmetry increases with habitat disturbance in seven bird species of a fragmented afrotropical Forest
Proceedings of The Royal Society B: Biological Sciences, 1999Co-Authors: Luc Lens, S Van Dongen, Christine M Wilder, Thomas M Brooks, Erik MatthysenAbstract:We studied fluctuating asymmetry (FA) in the tarsus length of seven Forest-restricted bird species, two of which are globally critically endangered, in three Indigenous Forest remnants of a recently fragmented, afrotropical biodiversity hot spot. Based on mixed regression analysis and an extension of Levene's test, individuals from the most degraded fragment showed four- to sevenfold higher asymmetry levels compared to those from the least degraded one, with intermediate levels in the moderately disturbed fragment. When comparing contemporary FA levels with measurements of museum specimens collected 50 years ago, we found highly significant increases in asymmetry in the most degraded fragment but no differences in the least degraded one. These strikingly parallel spatial and temporal patterns across species confirm that repeated measurements of FA can provide a sensitive early warning system for monitoring stress effects in highly threatened ecosystems.
Aliza Roux - One of the best experts on this subject based on the ideXlab platform.
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Samango Monkeys (Cercopithecus albogularis labiatus) Manage Risk in a Highly Seasonal, Human-Modified Landscape in Amathole Mountains, South Africa
International Journal of Primatology, 2017Co-Authors: Katarzyna Nowak, Kirsten Wimberger, Shane A. Richards, Russell A. Hill, Aliza RouxAbstract:Wild species use habitats that vary in risk across space and time. This risk can derive from natural predators and also from direct and indirect human pressures. A starving forager will often take risks that a less hungry forager would not. At a highly seasonal and human-modified site, we predicted that arboreal samango monkeys ( Cercopithecus albogularis labiatus ) would show highly flexible, responsive, risk-sensitive foraging. We first determined how monkeys use horizontal and vertical space across seasons to evaluate if high-risk decisions (use of gardens and ground) changed with season, a proxy for starvation risk. Then, during a subsequent winter, we offered equal feeding opportunities (in the form of high-value, raw peanuts) in both gardens and Forest to see if this short-term change in food availability and starvation risk affected monkeys’ foraging decisions. We found that during the food-scarce winter, monkeys foraged outside Indigenous Forest and in gardens, where they fed on exotic species, especially fallen acorns ( Quercus spp.), despite potential threats from humans. Nevertheless, and as predicted, when given the choice of foraging on high-value foods in gardens vs. Forest during our artificial foraging experiment, monkeys showed a preference for a safer Forest habitat. Our experiment also indicated monkeys’ sensitivity to risk in the lower vertical strata of both habitats, despite their previous extensive use of the ground. Our findings support one of the central tenets of optimal foraging theory: that risk of starvation and sensitivity to the variation in food availability can be as important drivers of behavior as risk of predation.
S E Piper - One of the best experts on this subject based on the ideXlab platform.
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the influence of climate change on the distribution of Indigenous Forest in kwazulu natal south africa
Journal of Biogeography, 1999Co-Authors: Harriet A C Eeley, Michael J Lawes, S E PiperAbstract:Aims (1) To define the physical correlates of Indigenous Forest in KwaZulu-Natal province and develop a model, based on climatic parameters, to predict the potential distribution of Forest subtypes in the province. (2) To explore the impact of palaeoclimatic change on Forest distribution, providing an insight into the regional-scale/historical forces shaping the pattern and composition of present-day Forest communities. (3) To investigate potential future shifts in Forest distribution associated with projected climate change.