Browsing by Autor "Erik Matthysen"

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Bird species richness in High-Andean forest fragments: habitat quality and topography matter
(2020) Constance Fastré; Diederik Strubbe; José Antonio Balderrama; Jennifer R. A. Cahill; Hannes Ledegen; Mauricio Torrico Orellana; Erik Matthysen
Montane forests worldwide are known centers of endemism and biodiversity but are highly threatened by fragmentation processes. Using data collected in 15 Polylepis forest remnants covering 2000 hectares, we investigated how bird species richness and bird community composition, particularly for species of conservation concern, are influenced by habitat quality and topography in the Tunari National Park in the High Andes of Bolivia. Bird species richness was highest in topographically complex, low-elevation Polylepis patches located in areas with a high potential to retain rainwater. Bird communities differed strongly between Polylepis lanata and P. subtusalbida remnants, each supporting different threatened and endemic species. Within the P. subtusalbida forest, high-elevation fragments characterized by high amounts of sunlight and low anthropogenic disturbance were more likely to contain threatened species. Surprisingly, we found no effect of fragment size on the diversity or composition of bird communities or the presence of bird species of conservation concern. The presence of exotic plantations (Pinus and/or Eucalyptus spp.) in or outside forest remnants was negatively associated with the number of bird species as well as with occurrence of the endangered Cochabamba-mountain finch (Compsospiza garleppi). To support the different communities found in Polylepis forests, these results suggest that conservation efforts should be directed towards both forest types (P. subtusalbida and P. lanata) present in the area. For an efficient management of avian diversity, exotic plantations should be established away from native remnants while existing patches should be managed to maintain or increase habitat quality. Finally, the importance of local topography in determining avian species richness and community composition in forest fragments, mainly through topographic controls on moisture distribution and the amount of sunlight received by the fragments, should be considered when planning conservation and reforestation schemes.
Consistency and variation in the bat assemblages inhabiting two forest islands within a neotropical savanna in Bolivia
(Cambridge University Press, 2003) Luís F. Aguirre; Luc Lens; Raoul Van Damme; Erik Matthysen
Neotropical bats occupy a large variety of trophic niches, and represent locally abundant, species-rich communities. As such, they are highly suited as a model group for the study of temporal and spatial dynamics of animal communities. However, despite this important research potential, data on the dynamics and turnover rates of Neotropical bat communities are lacking. We here study both aspects for bats inhabiting two natural forests surrounded by savanna in Bolivia. Over a period of 8 y, both bat communities showed high rates of species turnover. As predicted, species relying on fluctuating food resources were more likely to be absent in particular years, whereas species relying on more predictable food supplies were present in all years.
Ecomorphological analysis of trophic niche partitioning in a tropical savannah bat community
(Royal Society, 2002) Luís F. Aguirre; Anthony Herrel; Raoul Van Damme; Erik Matthysen
The exceptional diversity of neotropical bat communities is sustained by an intricate partitioning of available resources among the member species. Trophical specialization is considered an important evolutionary avenue towards niche partitioning in neotropical phyllostomid bats. From an ancestral insectivorous condition, phyllostomids evolved into highly specialized frugivorous, carnivorous, nectarivorous, piscivorous and even sanguivorous species. Previously, correlations between cranial morphology and trophic ecology within this group have been documented. Here, we examine the evolutionary relationships between bite force and head shape in over 20 species of bats from a single tropical savannah bat community. The results show that bite force increases exponentially with body size across all species examined. Despite the significant differences between large dietary groups using traditional analysis (i.e. non-phylogenetic) and the strong evolutionary correlations between body mass and bite force, phylogenetic analyses indicated no differences in bite performance between insectivorous, omnivorous and frugivorous bats. Comparisons of three species with highly specialized feeding habits (nectarivory, piscivory and sanguivory) with the rest of the species in the community indicate that specialization into these niches comes at the expense of bite performance and, hence, may result in a reduction of the trophic niche breadth.
Effects of variable selection on modelling habitat and potential distribution of the Andean bear in Bolivia
(2013) Ximena Velez–Liendo; Diederik Strubbe; Erik Matthysen
Species distribution models are used in ecology and conservation biology to draw inferences about the drivers of species' ranges. However, poor conceptual background, environmental variable selection, and algorithm selection can contribute to misleading model predictions. We assessed the effects of environment variable selection and compared statistical performance and output maps of correlative resource- and biotope-based models for estimating the habitat and potential distribution of the Andean bear (Tremarctos ornatus) in Bolivia's Tropical Andes. The resource-based approach estimated bear habitat using 7 resources associated with 3 ecological functions: feeding, shelter, and access to water. In contrast, the biotope model described the habitat by applying 11 environmental predictors related to topography, vegetation, and human activities. Both models performed equally well overall and better than random, with shelter as the most influential variable for the resource model and Yunga forest for the biotope model. However, discrepancies in the extent and arrangement of predicted bear distribution between models differed and emphasized the effect of variable selection, which could influence the delineation of conservation areas for this species. We suggest using a resource-based approach when modelling species distribution because of the more direct relationship to the species investigated and greater ease of interpreting results.
Habitat use by two specialist birds in high-Andean Polylepis forests
(Elsevier BV, 2007) Jennifer R. A. Cahill; Erik Matthysen
Home range characteristics of the Near Threatened Giant Conebill Oreomanes fraseri in fragmented Polylepis forest
(Cambridge University Press, 2009) Greet De Coster; Erik Matthysen; Jennifer R. A. Cahill; Luc Lens
Summary The Giant Conebill Oreomanes fraseri is a specialist of high Andean Polylepis forest remnants. With the aid of radio-tracking and visual observations, the average 100% minimum convex polygon home range size of seven adult individuals was 7.15 ha. Range size decreased with increasing tree density, and for equal tree densities, it was larger in the study site with larger Polylepis fragments. Home ranges often comprised areas that were largely or entirely devoid of trees. Within home ranges, space use significantly varied with time of day, and this pattern tended to be largely consistent among days. Given the large extent of variation in size and structure already observed in this small sample of home ranges, we suggest that apart from the size, shape, structure and degree of isolation of the remaining forest patches, also their topographic location, and hence sun exposure, may be an important consideration when designing conservation strategies for Giant Conebill.
Landscape assessment of habitat suitability and connectivity for Andean bears in the Bolivian Tropical Andes
(2014) Ximena Velez–Liendo; Frank Adriaensen; Erik Matthysen
The survival of large and mobile species in the face of habitat loss and fragmentation depends on several factors, including the landscape configuration of subpopulations and the dispersal capabilities of the species. We performed a landscape analysis of the Bolivian Tropical Andes to determine whether remaining habitat patches were suitable in terms of ecological characteristics and potential connectivity for the long-term survival of the Andean bear (Tremarctos ornatus). First we built a ruled-based model to identify key patches or areas large enough to sustain a viable population by using knowledge of Andean bear habitat requirements and movement patterns. Second, we estimated potential functional connectivity among these areas applying a cost-distance analysis based on estimates of the resistance to movement through the landscape. Finally, we quantified the proportion of these key patches and corridor habitats within the Bolivian protected area system. The rule-based model identified 13 key patches covering 21,113 km2 corresponding to a maximum estimated population of 3,165 adult bears. Using cost-distance analysis, all 13 key patches were potentially connected to ≥1 other key patch. Twelve of the patches were at least partially protected by national parks, and 40% of areas considered suitable as corridors were included within a protected area. Although the current protected area system includes suitable bear habitat, large portions of key patches and corridors are unprotected, which could eventually lead to fragmentation and habitat loss if these areas are not protected.
Lower density of arthropod biomass in small high‐Andes Polylepis fragments affects habitat use in insectivorous birds
(Wiley, 2021) Jennifer R. A. Cahill; Thomas Merckx; Hans Van Dyck; Milton Fernández; Erik Matthysen
Abstract Polylepis forests are endemic to the high‐Andes, with trees characterized by multi‐layered, exfoliating bark‐providing protection against harsh, high‐elevation conditions, both for individual trees and the wide array of organisms dependent on them. However, Polylepis habitat has suffered severe human‐induced land conversion and currently mainly occurs as fragmented remnants only. Here, we studied the effects of fragment size on local ambient temperature and on biomass of bark and its bark‐dwelling arthropods. We did so by comparing multiple samples at the edge and interior of both large and small fragments, while also accounting for branch size, tree width, and tree structure. Because arthropod biomass is likely to impact higher trophic levels, we also studied abundance and foraging behavior of two bird species specialized on Polylepis forest. We show that arthropod biomass was relatively higher in wider, larger trees, which were preferred for foraging by both bird species. Moreover, we show that small forest fragments are not only environmentally less buffered but are also characterized by lower amounts of bark and lower densities of bark‐dwelling arthropods than larger fragments. Our study highlights the conservation value of large trees. Also, we advise it is now timely to test to what degree restoration efforts to increase fragment size could mitigate the negative effects of reduced arthropod biomass for higher trophic levels of endemic specialist insectivores.
Nesting biology of the Giant Conebill (Oreomanes fraseri) in the High Andes of Bolivia
(Wilson Ornithological Society, 2008) Jennifer R. A. Cahill; Erik Matthysen; Noemí Huanca
Eight nests of the Giant Conebill (Oreomanes fraseri, Family Thraupidae) were found in Polylepis forest fragments in Cochabamba Department (Sacha Loma and Cuturi) of Bolivia during 2002–2004. The breeding period of the Giant Conebill extended from September to December at the beginning of the rainy season. The nests were open cups with an average outside width of 20 cm and a thick rim of 5.5 cm; the average clutch size was 1.86. Nests were constructed mostly with parts of Polylepis trees and a variety of mosses. All nests located were in the interior of forests, well camouflaged, and in trees with an average height of 3.16 m. Control of human disturbance, especially burning, is needed for protection of the habitat of the Giant Conebill.
Patterns of roost use by bats in a neotropical savanna: implications for conservation
(Elsevier BV, 2003) Luís F. Aguirre; Luc Lens; Erik Matthysen
SEASONAL VARIATION IN AVIAN COMMUNITY COMPOSITION IN A HIGH-ANDEAN POLYLEPIS (ROSACEAE)FOREST FRAGMENT
(2003) Sebastián K. Herzog; RODRIGO SORIA A.; Erik Matthysen
We analyzed seasonal variation in avian species richness and relative abundance at the community and guild level during a 13-month period in central Bolivia in an 11-ha patch of Polylepis (Rosaceae) forest, a high-Andean ecosystem that has suffered from extreme anthropogenic fragmentation. Birds were surveyed audio-visually (supplemented with mist net data) and assigned to five relative abundance categories for 2-month survey periods. We recorded 35 core species, including 16 insectivores (46%), 11 frugi-granivores (31%), seven nectarivores (20%), and one carnivore (3%). Core species richness varied from 25 (June–July) to 33 (October–November). Insectivores had a significantly higher proportion of year-round residents (81%) than frugi-granivores (45%) or nectarivores (14%); the same trend was evident with respect to seasonal variation in species richness of each guild. Although most species varied considerably in their relative abundance, no guild showed significant variation in relative abundance scores among survey periods. However, frugi-granivores and nectarivores combined, both of which depend upon plants as food resources, reached a significant minimum in mid-winter (June–July), and the same result was found at the community level. The insectivore guild thus was the most temporally stable both in terms of species richness and abundance. Qualitative observations indicated that the fluctuations in frugi-granivores and nectarivores were related to the availability of food resources.
The implications of food hardness for diet in bats
(Wiley, 2003) Luís F. Aguirre; Anthony Herrel; Raoul Van Damme; Erik Matthysen
Summary Neotropical bat communities are characterized by a broad species diversity, which can be achieved and maintained only through partitioning of the available resources. Here patterns of trophic resource utilization within a single neotropical savanna bat community are investigated. Moreover, the physical properties of food items (i.e. hardness), its variation with food size, and whether food hardness differs between items consumed by the bats in this community are investigated experimentally. The results show that food hardness increases with the size of the food item, and that distinct differences exist in the amount of force needed to crush different food items (beetles vs other insects vs fruits). Using previously published data on bite forces from species in the same community it is explored whether food hardness may play a role in shaping the diets of the bats in the community. The combined data on bite forces and food hardness indicate that food hardness can both directly and indirectly limit dietary diversity in bats. The results also indicate that dietary specialization may potentially result in a decrease in trophic breadth for some species through its effect on bite performance.