Persistence of Forest Birds in the Costa Rican Agricultural Countryside

Abstract:  Understanding the persistence mechanisms of tropical forest species in human-dominated landscapes is a fundamental challenge of tropical ecology and conservation. Many species, including more than half of Costa Rica's native land birds, use mostly deforested agricultural countryside, but how they do so is poorly known. Do they commute regularly to forest or can some species survive in this human-dominated landscape year-round? Using radiotelemetry, we detailed the habitat use, movement, foraging, and nesting patterns of three bird species, Catharus aurantiirostris , Tangara icterocephala , and Turdus assimilis , by obtaining 8101 locations from 156 individuals. We chose forest birds that varied in their vulnerability to deforestation and were representative of the species found both in forest and human-dominated landscapes. Our study species did not commute from extensive forest; rather, they fed and bred in the agricultural countryside. Nevertheless, T. icterocephala and T. assimilis , which are more habitat sensitive, were highly dependent on the remaining trees. Although trees constituted only 11% of land cover, these birds spent 69% to 85% of their time in them. Breeding success of C. aurantiirostris and T. icterocephala in deforested habitats was not different than in forest remnants, where T. assimilis experienced reduced breeding success. Although this suggests an ecological trap for T. assimilis , higher fledgling survival in forest remnants may make up for lower productivity. Tropical countryside has high potential conservation value, which can be enhanced with even modest increases in tree cover. Our findings have applicability to many human-dominated tropical areas that have the potential to conserve substantial biodiversity if appropriate restoration measures are taken.     

Habitat-tree protection concepts over 200 years

The protection and sustainable management of habitat trees is an integral part of modern forest nature conservation concepts such as retention forestry. Bats, cavity-nesting birds, arboreal marsupials, and many different saproxylic species depend on habitat trees and their great variety of microhabitats and old-growth characteristics. With a focus on insights from temperate forests, we traced the development of habitat-tree protection over 200 years. The idea was first conceptualized by foresters and natural scientists in the early 19th century. At that time, utilitarian conservation aimed to protect cavity trees that provided roosts and nesting holes for insectivorous bats and birds. By the second half of the 19th century, habitat-tree protection was well known to foresters and was occasionally implemented. Knowledge of the protection of large old trees, a special kind of habitat tree, for sociocultural and aesthetic reasons developed similarly. But, many foresters of that time and in the following decades fundamentally rejected protection of habitat trees for economic reasons. Beginning in the 1970s, forest conservation and integrative forest management became increasingly important issues worldwide. Since then, the protection of habitat trees has been implemented on a large scale. Long-term views on the development of conservation concepts are important to inform the implementation of conservation today. In particular, historical analyses of conservation concepts allow the testing of long-term conservation outcomes and make it possible to study the resilience of conservation approaches to changing social or ecological conditions. We encourage all conservation ecologists to assess the practical and conceptual impact of the initial ideas that led to modern conservation concepts in terms of long-term biodiversity conservation.     

Long-Term Avifaunal Impoverishment in an Isolated Tropical Woodlot

Abstract:  Long-term (>50 years) extinction patterns and processes in isolated tropical forest patches are poorly understood. Considering that forest fragments are rapidly becoming the common feature of most tropical landscapes, data on the long-term conservation value of such fragments are urgently needed. We report on avifaunal turnover in a tropical woodlot (Bogor Botanical Gardens; 86 ha; 54% native and 46% introduced plants; mean 83,649 visitors/month) that has been surveyed several times before and after its isolation in 1936. By 2004 the original avifaunal richness of this woodlot declined by 59% (97 to 40 species) and its forest-dependent avifauna declined by 60% (30 to 12 species). Large-bodied birds were particularly prone to extinction before 1987, but following this time none of the species traits we studied could be considered predictive of extinction proneness. All seven forest-dependent bird species that attempted to colonize this woodlot by 1987 perished thereafter. Our results show that area reduction, isolation, intense human use, and perverse management (e.g., understory removal) of this patch have probably negatively affected the long-term sustainability of its forest avifauna.     

Songbird Use of Gallery Woodlands in Recently Cleared and Older Settled Landscapes of the Selva Lacandona, Chiapas, Mexico

Many regions of Central America have undergone wide-scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern México. Two study areas were established on lands that had been cleared and settled 20–35 and 10 years previously. Our objectives were to assess the value of arroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance of songbirds in cleared areas settled at different times over a 35-year period. Arroyo vegetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest-dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation are protected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land-use practices currently in use.     

Evaluating the Success of Conservation Actions in Safeguarding Tropical Forest Biodiversity

Abstract: We reviewed the evidence on the extent and efficacy of conservation of tropical forest biodiversity for each of the classes of conservation action defined by the new International Union for Conservation of Nature (IUCN) classification. Protected areas are the most tested conservation approach, and a number of studies show they are generally effective in slowing deforestation. There is some documentation of the extent of sustainable timber management in tropical forest, but little information on other landscape‐conservation tactics. The extent and effectiveness of ex situ species conservation is quite well known. Forty‐one tropical‐forest species now survive only in captivity. Other single‐species conservation actions are not as well documented. The potential of policy mechanisms, such as international conventions and provision of funds, to slow extinctions in tropical forests is considerable, but the effects of policy are difficult to measure. Finally, interventions to promote tropical conservation by supporting education and livelihoods, providing incentives, and furthering capacity building are all thought to be important, but their extent and effectiveness remain poorly known. For birds, the best studied taxon, the sum of such conservation actions has averted one‐fifth of the extinctions that would otherwise have occurred over the last century. Clearly, tropical forest conservation works, but more is needed, as is critical assessment of what works in what circumstances, if mass extinction is to be averted.     

Application of Extinction and Conservation Theories for Forest Birds in Nicaragua

Abstract: An increasing number of empirical studies have been done on the effects of tropical forest fragmentation on avian communities, but few researchers have applied these theories to assess the vulnerability of birds in poorly researched countries such as Nicaragua. I used a logistic regression to determine which natural-history characteristics were most important in predicting a list of threatened birds known to occur in Nicaragua. The best model included five macroecological variables ( body weight, habitat specificity, trophic group, forest preference, and biogeography within Nicaragua). I used this model to generate predicted probabilities of extinction for all forest birds in Nicaragua. The predicted probability of extinction from the best model ranked 63% of the extinction-prone birds from La Selva, Costa Rica, and 59% of the extinction-prone birds from Barro Colorado, Panama, in the first quartile of all forest birds recorded in Nicaragua. This method provides a first-order approximation of which species deserve global and national priorities for conservation. The central and Atlantic regions of Nicaragua deserve high priority for conservation at a global scale, whereas the Atlantic region deserves the highest priority for conservation at a national scale. The Nicaraguan Ministry of Natural Resources and the Environment has done an adequate job of identifying areas for conservation based on the proportion of decreed nature reserves in each biogeographic region and the distribution of forest birds with a high predicted probability of extinction. Forest birds in central Nicaragua, however, may currently be the most vulnerable to local extinction because of low forest cover within decreed reserves.     

Cost‐Effectiveness of Using Small Vertebrates as Indicators of Disturbance

In species‐rich tropical forests, effective biodiversity management demands measures of progress, yet budgetary limitations typically constrain capacity of decision makers to assess response of biological communities to habitat change. One approach is to identify ecological‐disturbance indicator species (EDIS) whose monitoring is also monetarily cost‐effective. These species can be identified by determining individual species’ responses to disturbance across a gradient; however, such responses may be confounded by factors other than disturbance. For example, in mountain environments the effects of anthropogenic habitat alteration are commonly confounded by elevation. EDIS have been identified with the indicator value (IndVal) metric, but there are weaknesses in the application of this approach in complex montane systems. We surveyed birds, small mammals, bats, and leaf‐litter lizards in differentially disturbed cloud forest of the Ecuadorian Andes. We then incorporated elevation in generalized linear (mixed) models (GL(M)M) to screen for EDIS in the data set. Finally, we used rarefaction of species accumulation data to compare relative monetary costs of identifying and monitoring EDIS at equal sampling effort, based on species richness. Our GL(M)M generated greater numbers of EDIS but fewer characteristic species relative to IndVal. In absolute terms birds were the most cost‐effective of the 4 taxa surveyed. We found one low‐cost bird EDIS. In terms of the number of indicators generated as a proportion of species richness, EDIS of small mammals were the most cost‐effective. Our approach has the potential to be a useful tool for facilitating more sustainable management of Andean forest systems. Rentabilidad del Uso de Pequeños Vertebrados como Indicadores de Perturbaciones     

Assessing Habitat Quality for a Migratory Songbird Wintering in Natural and Agricultural Habitats

Abstract:  As tropical forests are cleared, a greater proportion of migratory songbirds are forced to winter in agricultural and disturbed habitats, which, if poorer in quality than natural forests, could contribute to population declines. We compared demographic indicators of habitat quality for a focal species, the American Redstart ( Setophaga ruticilla ), wintering in Jamaican citrus orchards and shade coffee plantations with those in four natural habitats: mangrove, coastal scrub, coastal palm, and dry limestone forests. Demographic measures of habitat quality included density, age and sex ratio, apparent survival, and changes in body mass. Measures of habitat quality for redstarts in citrus and coffee habitats were generally intermediate between the highest (mangrove) and lowest (dry limestone) measurements from natural habitats. The decline in mean body mass over the winter period was a strong predictor of annual survival rate among habitats, and we suggest that measures of body condition coupled with survival data provide the best measures of habitat quality for nonbreeding songbirds. Density, which is far easier to estimate, was correlated with these more labor-intensive measures, particularly in the late winter when food is likely most limiting. Thus, local density may be useful as an approximation of habitat quality for wintering migrant warblers. Our findings bolster those of previous studies based on bird abundance that suggest arboreal agricultural habitats in the tropics can be useful for the conservation of generalist, insectivorous birds, including many migratory passerines such as redstarts.     

Birds as predators in tropical agroforestry systems

Insectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, studies where predation by birds has been assessed. The variation in bird effects may be due to characteristics such as plant productivity or quality, habitat complexity, and/or species diversity of predator and prey assemblages. Since agroforestry systems vary in such characteristics, these systems provide a good starting point for understanding when and where we can expect predation by birds to be important. We analyze data from bird exclosure studies in forests and agroforestry systems to ask whether birds consistently reduce their arthropod prey base and whether bird predation differs between forests and agroforestry systems. Further, we focus on agroforestry systems to ask whether the magnitude of bird predation (1) differs between canopy trees and understory plants, (2) differs when migratory birds are present or absent, and (3) correlates with bird abundance and diversity. We found that, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage. We observed no difference in the magnitude of bird effects between agroforestry systems and forests despite simplified habitat structure and plant diversity in agroforests. Within agroforestry systems, bird reduction of arthropods was greater in the canopy than the crop layer. Top-down effects of bird predation were especially strong during censuses when migratory birds were present in agroforestry systems. Importantly, the diversity of the predator assemblage correlated with the magnitude of predator effects; where the diversity of birds, especially migratory birds, was greater, birds reduced arthropod densities to a greater extent. We outline potential mechanisms for relationships between bird predator, insect prey, and habitat characteristics, and we suggest future studies using tropical agroforests as a model system to further test these areas of ecological theory.     

Conserving international coastal habitat networks on migratory waterfowl flyways

Migratory waterfowl depend on habitat networks at local, national and international scales for their survival. Coastal habitats are key areas for many waterfowl. Different species use different biotopes and in different places, so overall many parts of the coastal resource are important. As well as national conservation efforts, waterfowl conservation is increasingly focussed worldwide on collaborative international conservation, catalysed by several measures e.g. the Ramsar Convention, the EC Conservation of Wild Birds Directive, and the Bonn Convention Agreement on the Conservation of African/Eurasian Migratory Waterbirds. Several international conservation plans are under development for single species, but a more effective approach may be to develop plans, for assemblages of migratory birds with similar habitat requirements. All such plans must incorporate future sustainable use of the habitats on which the birds depend. Yet migratory bird and coastal habitat conservation is still often approached separately, despite the two being now closely linked to the development of the Natura 2000 site network in the European Community. Implementing the 1992 EC Habitats Directive requires the selection of coastal habitat sites for designation, set in national and international contexts of resource distribution. International coastal habitat inventories are needed to underpin this process. Combining such inventories with assessment of the flyway habitat requirements of waterfowl species and assemblages offers great potential for identifying international coastal habitat networks that meet the objectives of both habitat and migratory waterfowl conservation.     

Refining Biodiversity Conservation Priorities

Abstract:  Although there is widespread agreement about conservation priorities at large scales (i.e., biodiversity hotspots), their boundaries remain too coarse for setting practical conservation goals. Refining hotspot conservation means identifying specific locations (individual habitat patches) of realistic size and scale for managers to protect and politicians to support. Because hotspots have lost most of their original habitat, species endemic to them rely on what remains. The issue now becomes identifying where this habitat is and these species are. We accomplished this by using straightforward remote sensing and GIS techniques, identifying specific locations in Brazil's Atlantic Forest hotspot important for bird conservation. Our method requires a regional map of current forest cover, so we explored six popular products for mapping and quantifying forest: MODIS continuous fields and a MODIS land cover (preclassified products), AVHRR, SPOT VGT, MODIS (satellite images), and a GeoCover Landsat thematic mapper mosaic (jpg). We compared subsets of these forest covers against a forest map based on a Landsat enhanced thematic mapper. The SPOT VGT forest cover predicted forest area and location well, so we combined it with elevation data to refine coarse distribution maps for forest endemic birds. Stacking these species distribution maps enabled identification of the subregion richest in threatened birds—the lowland forests of Rio de Janeiro State. We highlighted eight priority fragments, focusing on one with finer resolved imagery for detailed study. This method allows prioritization of areas for conservation from a region >1 million km² to forest fragments of tens of square kilometers. To set priorities for biodiversity conservation, coarse biological information is sufficient. Hence, our method is attractive for tropical and biologically rich locations, where species location information is sparse.     

Environmental Synergisms and Extinctions of Tropical Species

Abstract: Environmental synergisms may pose the greatest threat to tropical biodiversity. Using recently updated data sets from the International Union for Conservation of Nature (IUCN) Red List, we evaluated the incidence of perceived threats to all known mammal, bird, and amphibian species in tropical forests. Vulnerable, endangered, and extinct species were collectively far more likely to be imperiled by combinations of threats than expected by chance. Among 45 possible pairwise combinations of 10 different threats, 69%, 93%, and 71% were significantly more frequent than expected for threatened mammals, birds, and amphibians, respectively, even with a stringent Bonferroni‐corrected probability value (p= 0.003). Based on this analysis, we identified five key environmental synergisms in the tropics and speculate on the existence of others. The most important involve interactions between habitat loss or alteration (from agriculture, urban sprawl, infrastructure, or logging) and other anthropogenic disturbances such as hunting, fire, exotic‐species invasions, or pollution. Climatic change and emerging pathogens also can interact with other threats. We assert that environmental synergisms are more likely the norm than the exception for threatened species and ecosystems, can vary markedly in nature among geographic regions and taxa, and may be exceedingly difficult to predict in terms of their ultimate impacts. The perils posed by environmental synergisms highlight the need for a precautionary approach to tropical biodiversity conservation.     

Use of opportunistic sightings and expert knowledge to predict and compare Whooping Crane stopover habitat

Predicting a species’ distribution can be helpful for evaluating management actions such as critical habitat designations under the U.S. Endangered Species Act or habitat acquisition and rehabilitation. Whooping Cranes (Grus americana) are one of the rarest birds in the world, and conservation and management of habitat is required to ensure their survival. We developed a species distribution model (SDM) that could be used to inform habitat management actions for Whooping Cranes within the state of Nebraska (U.S.A.). We collated 407 opportunistic Whooping Crane group records reported from 1988 to 2012. Most records of Whooping Cranes were contributed by the public; therefore, developing an SDM that accounted for sampling bias was essential because observations at some migration stopover locations may be under represented. An auxiliary data set, required to explore the influence of sampling bias, was derived with expert elicitation. Using our SDM, we compared an intensively managed area in the Central Platte River Valley with the Niobrara National Scenic River in northern Nebraska. Our results suggest, during the peak of migration, Whooping Crane abundance was 262.2 (90% CI 40.2?3144.2) times higher per unit area in the Central Platte River Valley relative to the Niobrara National Scenic River. Although we compared only 2 areas, our model could be used to evaluate any region within the state of Nebraska. Furthermore, our expert‐informed modeling approach could be applied to opportunistic presence‐only data when sampling bias is a concern and expert knowledge is available.     

Conservation of Species in Dynamic Landscapes: Divergent Fates of Silene tatarica Populations in Riparian Habitats

Abstract:  In transient environments, where local extinctions occur as a result of destruction or deterioration of the local habitat, the long-term persistence of a species requires successful colonizations at new, suitable sites. This kind of habitat tracking should be associated with the asynchronous dynamics of local populations, and it can be especially important for the conservation of rare plant species in riparian habitats. We determined spatiotemporal variation in the demography of the perennial Silene tatarica (L.) Pers. in 15 populations (1998–2003) located in periodically disturbed riparian habitats. The habitats differed according to their morphology (flat shores, slopes) and the amount of bare ground (open, intermediate, closed) along a successional gradient. We used elasticity and life-table response analyses and stochastic simulations to study the variation in population demography. Finite population growth rate was higher in intermediate habitats than in open and closed habitats. In stochastic simulations population size increased in most cases, but four populations were projected to become extinct within 12–70 years. The viability of local populations depended most on the survival and growth of juvenile individuals and on the fecundity of large fertile individuals. On a regional scale, the persistence of this species will require a viable network of local populations as protection against local extinctions caused by natural disturbances and succession. Accordingly, the long-term persistence of riparian species may depend on habitat changes; thus, their conservation requires maintenance of natural disturbance dynamics. Along regulated rivers, management activities such as the creation of open habitats for new colonization should be implemented. Similarly, these activities can be rather general requirements for the conservation of endangered species dependent on transient habitats along successional gradients.     

Landscape-level impact of tropical forest loss and fragmentation on bird occurrence in eastern Guatemala

Tropical forest destruction and fragmentation of habitat patches may reduce population persistence at the landscape level. Given the complex nature of simultaneously evaluating the effects of these factors on biotic populations, statistical presence/absence modelling has become an important tool in conservation biology. This study uses logistic regression to evaluate the independent effects of tropical forest cover and fragmentation on bird occurrence in eastern Guatemala. Logistic regression models were constructed for 10 species with varying response to habitat alteration. Predictive variables quantified forest cover, fragmentation and their interaction at three different radii (200, 500 and 1000 m scales) of 112 points where presence of target species was determined. Most species elicited a response to the 1000 m scale, which was greater than most species’ reported territory size. Thus, their presence at the landscape scale is probably regulated by extra-territorial phenomena, such as dispersal. Although proportion of forest cover was the most important predictor of species’ presence, there was strong evidence of area-independent and -dependent fragmentation effects on species presence, results that contrast with other studies from northernmost latitudes. Species’ habitat breadth was positively correlated with AIC model values, indicating a better fit for species more restricted to tropical forest. Species with a narrower habitat breadth also elicited stronger negative responses to forest loss. Habitat breadth is thus a simple measure that can be directly related to species’ vulnerability to landscape modification. Model predictive accuracy was acceptable for 4 of 10 species, which were in turn those with narrower habitat breadths.     

Impacts of tropical forest disturbance on species vital rates

Tropical forests are experiencing enormous threats from deforestation and habitat degradation. Much knowledge of the impacts of these land-use changes on tropical species comes from studies examining patterns of richness and abundance. Demographic vital rates (survival, reproduction, and movement) can also be affected by land-use change in a way that increases species vulnerability to extirpation, but in many cases these impacts may not be manifested in short-term changes in abundance or species richness. We conducted a literature review to assess current knowledge and research effort concerning how land-use change affects species vital rates in tropical forest vertebrates. We found a general paucity of empirical research on demography across taxa and regions, with some biases toward mammals and birds and land-use transitions, including fragmentation and agriculture. There is also considerable between-species variation in demographic responses to land-use change, which could reflect trait-based differences in species sensitivity, complex context dependencies (e.g., between-region variation), or inconsistency in methods used in studies. Efforts to improve understanding of anthropogenic impacts on species demography are underway, but there is a need for increased research effort to fill knowledge gaps in understudied tropical regions and taxa. The lack of information on demographic impacts of anthropogenic disturbance makes it difficult to draw definite conclusions about the magnitude of threats to tropical ecosystems under anthropogenic pressures. Thus, determining conservation priorities and improving conservation effectiveness remains a challenge.     

Effects of anthropogenic disturbance on primate density at the landscape scale

Accurate estimations of the abundance of threatened animal populations are required for assessment of species’ status and vulnerability and conservation planning. However, density estimation is usually difficult and resource demanding, so researchers often collect data at local scales. However, anthropogenic pressures most often have landscape-level effects, for example, through habitat loss and fragmentation. We applied hierarchical distance sampling (HDS) to transect count data to determine the effect of habitat and anthropogenic factors on the density of 3 arboreal primate species inhabiting 5 distinct tropical forests across a landscape of 19,000 km² in the Udzungwa Mountains of Tanzania. We developed a novel, multiregion extension of HDS that allowed us to model density and detectability jointly across forests without losing site-specific information. For all species, the effect of anthropogenic disturbance on density was overwhelmingly negative among metapopulations: −0.63 Angolan colobus (Colobus angolensis palliatus) (95% Bayesian CI −1.03 to −0.27), −0.54 Udzungwa red colobus (Procolobus gordonorum) (−0.89 to −0.22), and −0.33 Sykes' monkey (Cercopithecus mitis monoides) (−0.63 to −0.07). Some responses to habitat factors were shared, notably the negative effect of elevation and the positive effect of climber coverage. These results are important for conservation science and practice because: the among-populations negative responses to anthropogenic disturbance provides a foundation for development of conservation plans that hold at the landscape scale, which is a comprehensive and cost-efficient approach; the among-species consistency in responses suggests conservation measures may be generalized at the guild level, which is especially relevant given the functional importance of primates in tropical rainforests; and the greater primate densities in areas at low elevation, which are closer to human settlements, point to specific management recommendations, such as the creation of buffer zones and prioritization of areas for protection.     

Lands for Long-Term Research in Conservation Biology

Abstract: Success in conservation biology depends upon a synergistic combination of short-term tactics and long-term strategies. Although the former are often necessary to forestall immediate habitat losses, the latter provide the critical framework of understanding needed to develop effective short-term priorities. Although many conservation biologists now emphasize short-term tactics, prudence dictates the concomitant establishment of long-term research projects aimed at answering fundamental ecological questions.
One deterrent to amassing such long-term data bases, aside from time and funding, is a lack of suitable sites where such studies can be conducted on a large scale. We describe two established major land-holding networks in the United States that could serve as appropriate places to develop long-term studies: the National Science Foundation's Long-Term Ecological Research (LTER) sites, and the US. Department of Energy's National Environmental Research Parks (NERPs). Because they consist of established research facilities, both networks can provide conservation biologists with "low-cost" baseline information on ecological processes, as well as access to a number of representative terrestrial and aquatic habitats under more or less "controlled" conditions suitable for long-term studies. We recommend that conservation biologists explore the possibility of using these or similarly available sites in their research programs.     

Conservation of Epiphyte Diversity in an Andean Landscape Transformed by Human Land Use

Abstract: Epiphytes are diverse and important elements of tropical forests, but as canopy‐dwelling organisms, they are highly vulnerable to deforestation. To assess the effect of deforestation on epiphyte diversity and the potential for epiphyte conservation in anthropogenically transformed habitats, we surveyed the epiphytic vegetation of an Ecuadorian cloud forest reserve and its surroundings. Our study was located on the western slopes of the Andes, a global center of biodiversity. We sampled vascular epiphytes of 110 study plots in a continuous primary forest; 14 primary forest fragments; isolated remnant trees in young, middle‐aged, and old pastures; and young and old secondary forests. It is the first study to include all relevant types of habitat transformation at a single study site and to compare epiphyte diversity at different temporal stages of fragmentation. Epiphyte diversity was highest in continuous primary forest, followed by forest fragments and isolated remnant trees, and lowest in young secondary forests. Spatial parameters of habitat transformation, such as fragment area, distance to the continuous primary forest, or distance to the forest edge from inside the forest, had no significant effect on epiphyte diversity. Hence, the influence of dispersal limitations appeared to be negligible or appeared to operate only over very short distances, whereas microclimatic edge effects acted only in the case of completely isolated trees, but not in larger forest fragments. Epiphyte diversity increased considerably with age of secondary forests, but species assemblages on isolated remnant trees were impoverished distinctly with time since isolation. Thus, isolated trees may serve for recolonization of secondary forests, but only for a relatively short time. We therefore suggest that the conservation of even small patches of primary forest within agricultural landscape matrices is essential for the long‐term maintenance of the high epiphyte diversity in tropical cloud forests.     

Effects of habitat fragmentation and degradation on flocks of African ant-following birds.

Tropical rain forests are rapidly cleared, fragmented, and degraded in sub-Saharan Africa; however, little is known about the response of species and even of key ecological groups to these processes. One of the most intriguing (but often neglected) ecological phenomena in African rain forests is the interaction between swarm-raiding army ants and ant-following birds. Similar to their well-known Neotropical representatives, ant-following birds in Africa track the massive swarm raids of army ants and feed on arthropods flushed by the ants. In this study we analyzed the effect of habitat fragmentation and degradation of a mid-altitude Congo-Guinean rain forest in western Kenya on the structure of ant-following bird flocks. Significant numbers of swarm raids were located in all forest fragments and in both undegraded and degraded forest. Fifty-six different species of birds followed army ant raids, forming bird flocks of one to 15 species. We quantitatively differentiated the bird community into five species of specialized ant-followers and 51 species of opportunistic ant-followers. Species richness and size of bird flocks decreased with decreasing size of forest fragments and was higher in undegraded than in degraded habitat. This was caused by the decrease of the species richness and number of specialized ant-followers at swarms, while the group of opportunistic ant-followers was affected little by habitat fragmentation and degradation. The composition of bird flocks was more variable in small fragments and degraded forest, compared to undegraded habitat in large fragments. The effect of habitat fragmentation on flock structure was best explained by the strong decline of the abundance of specialized ant-followers in small forest fragments. To conserve the association of army ants and ant-following birds in its natural state, vast areas of unfragmented and undegraded tropical rain forest are necessary.