Genetic Divergence During Long‐term Isolation in Highly Diverse Populations of Tropical Trees Across the Eastern Arc Mountains of Tanzania

The Eastern Arc Mountains are believed to support some of the oldest tropical forest in the world. The current distribution of this forest is highly fragmented due to a combination of long‐term effects of past changes in global climate and more recent deforestation. We sought to explore the hypothesized antiquity and long‐term isolation of the Eastern Arc montane forests based on an assessment of the geographical distribution and interspecies similarity of chloroplast DNA sequence variation in five forest trees. Data were used to investigate regional patterns of diversity and population structure based on intraspecific phylogenies, and results were interpreted against hypotheses on ecosystem age and connectivity. Regional diversity was high, with up to 22 chloroplast DNA haplotypes being recorded within a species across the sampled populations. Geographical concordance of genetic and geographic structure was weak to absent in all species and there was little similarity of genetic structure between species. Haplotype sharing between mountain blocks was extremely limited. The generally weak phylogeographical structure, in conjunction with high regional diversity and genetic uniqueness of individual mountain forests does not support the assumption of widespread genetic connectivity of the mountain forests, indicating instead a pattern of past isolation and ongoing diversification. Our findings substantially add to understanding patterns of diversity in this region and lend weight to calls to use more sophisticated biodiversity assessments when setting regional conservation and research funding priorities.     

Biogeography of the Shimba Hills ecosystem herpetofauna in Kenya

The Shimba Hills ecosystem along the south coast of Kenya is a key East African biodiversity hotspot.Historically, it is biogeographically assignable to the East African coastal biome. We examined the current Shimba Hills herpetofauna and their zoogeographical affinities to the coastal forests and nearby Eastern Arc Mountains biodiversity hotspots.The key studied sites included the Shimba Hills National Reserve, forest reserves, Kaya forests, and adjacent private land. Data on herpetofaunal richness were obtained from recent field surveys,literature, and specimens held at the National Museums of Kenya, Herpetology Section Collection,Nairobi. The Makadara, Mwele, and LongoMwagandi forests within the Shimba Hills National Reserve hosted the highest number of unique and rare species. Generally, the forest reserves and Kaya forests were important refuges for forestassociated species. On private land, Mukurumudzi Dam riparian areas were the best amphibian habitat and were host to three IUCN(Red List) EndangeredEN amphibian species, namely, Boulengerula changamwensis, Hyperolius rubrovermiculatus, and Afrixalus sylvaticus, as well as one snake species Elapsoidea nigra. Using herpetofauna as zoogeographic indicators, the Shimba Hills were determined to be at a crossroads between the coastal forests(13 endemic species) and the Eastern Arc Mountains(seven endemic species).Most of the Eastern Arc Mountains endemic species were from recent records, and thus more are likely to be found in the future. This 'hybrid' species richness pattern is attributable to the hilly topography of the Shimba Hills and their proximity to the Indian Ocean.This has contributed to the Shimba Hills being the richest herpetofauna area in Kenya, with a total of 89 and 38 reptile and amphibian species, respectively.Because of its unique zoogeography, the Shimba Hills ecosystem is undoubtedly a key biodiversity area for conservation investment.     

Camera trapping surveys of forest mammal communities in the Eastern Arc Mountains reveal generalized habitat and human disturbance responses

Large-bodied mammals are a rich and diversified faunal group in tropical rainforests. However, knowledge on community size and composition, and on species’ distribution and ecology remains often scant and inadequate against their chronic status of threats. We used camera trapping to detect mammals in the forests of the Eastern Arc Mountains (EAM) of Tanzania, a world renowned region for biodiversity comprised by a series of distinct and ancient mountain ranges partially covered in moist montane forest. We conducted surveys from 2003 to 2011 in eight of the 12 mountain blocks in Tanzania, and, through an overall sampling effort of 11,500 camera days, we detected 43 species. We normalized species richness and species’ detection events by effort, and used these metrics to assess the effect of habitat and human disturbance variables. We found that rarefied richness is positively affected by forest area at the block level, and that richness at forest patch level is also affected by forest area as well as surrounding human density (negative effect). For a subset of 17 species, we found consistent patterns of avoidance or tolerance of human disturbance and forest edges, and increased occurrence in areas at higher elevation, matching the historical forest loss that in most mountains occurred at lower elevation. Our study provides ecological insights that are novel for most species and sites, and reveals a general trend of negative impact of human disturbance on both community size and species’ relative abundance. Increased protection of the EAM forests in Tanzania is of urgent importance for the persistence of diversified mammal communities.     

Spatial variation and biogeography of sand forest avian assemblages in South Africa

Aim To examine biogeographical affiliations, habitat‐associated heterogeneity and endemism of avian assemblages in sand forest patches and the savanna‐like mixed woodland matrix. Location Two reserves in the Maputaland Centre of Endemism (MC) on the southern Mozambique Coastal Plain of northern KwaZulu‐Natal, South Africa. Methods Replicated surveys were undertaken in each of the two habitat types in each reserve, providing species abundance data over a full year. Vegetation structure at each of the survey sites was also quantified. Differences between the bird assemblages and the extent to which vegetation structure explained these differences were assessed using multi‐variate techniques. Biogeographical comparisons were based on species presence/absence data and clustering techniques. Results Bird assemblages differed significantly between habitats both within a given reserve and between reserves, and also between reserves for a given habitat. Differences in vegetation structure contributed substantially to differences between the avian assemblages. Of the four species endemic to the MC, three (Neergaard’s sunbird, Rudd’s apalis, and Woodward’s batis) were consistently present in sand forest. The fourth (pink‐throated twinspot) preferred mixed woodland. None of these endemic species was classed as rare. In the biogeographical analysis, both the sand forest and the mixed woodland bird assemblages were most similar to bird assemblages found in the forest biome or the Afromontane forest biome, depending on the biome classification used. Main conclusions The close affinities of sand forest and mixed woodland assemblages to those of the forest biome are most likely due to similarities in vegetation structure of these forests. Bird assemblages differ between the sand forest and mixed woodland habitats both within a given reserve and between reserves, and also between reserves for a given habitat. These differences extend to species endemic to the MC. Thus, conservation of sand forest habitat in a variety of areas is necessary to ensure the long‐term persistence of the biota.     

The role of local and regional processes in shaping dung beetle communities in tropical forest plantations in Borneo

We examine whether rain forest dung beetle species found in plantations in Sabah, northern Borneo, tend to be endemic or geographically widespread. In addition, linear regressions of abundance vs. distance from a major river in primary rain forest are calculated to see if species found in plantation forest show affinity to one specific biotope (riverine vs. interior forest) in their natural habitat. Results show that 14 of the 40 species recorded from plantations are endemic to Borneo. Only edge‐specialist endemic species are found in plantation forest, with no interior‐forest specialists recorded. Data suggest that endemic species that are adapted to more exposed conditions in primary rain forest, such as riverine species, can in some instances tolerate man‐made habitats. Twenty‐nine species (±SE 4.0) per transect are recorded from plantation transects, whereas 44.2 (±1.7 SE) are recorded in primary rain forest. As species richness is much lower in plantations than natural forest, implying loss of biodiversity, we conclude that measures of biogeographic distinctiveness, whereby endemic species confer higher values, may be misleading unless they take into account edge‐affinity. Local‐ as well as regional‐distributional data may therefore be needed to interpret correctly patterns of species assemblages in derived forest ecosystems.     

Three new species of Callulina (Amphibia: Anura: Brevicipitidae) highlight local endemism and conservation plight of Africa's Eastern Arc forests

Material ascribed to the genus Callulina from north‐east Tanzania and south‐east Kenya is assessed. Three new species of Callulina are described from the North ( Callulina laphami sp. nov. ) and South ( Callulina shengena sp. nov. and Callulina stanleyi sp. nov. ) Pare Mountains in Tanzania. The species are diagnosed based on morphological, acoustic, and molecular data. A new key to the species of Callulina is provided. Based on an interpretation of the International Union for Conservation of Nature (IUCN) red list, we suggest that the three species will qualify as critically endangered, because of their small distributions and the ongoing threat to their habitat. We reveal the high local endemism of Callulina in the northern part of the Eastern Arc Mountains, with each species restricted to no more than one mountain (fragment) block. This high local endemism in Callulina is probably widespread across the Eastern Arc, raising further conservation concern for this group of amphibians. Based on new molecular phylogenetic data for Callulina, we discuss biogeographical relationships among north‐east Tanzanian mountains, and evolutionary patterns in Eastern Arc breviciptids. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 496–514.     

Flightless insects: a test case for historical relationships of African mountains

Flightless insects give a clearer view of former distribution of montane habitat in Africa compared with highly mobile animals as birds and butterflies because passive long distance transport and long distance dispersal can be discounted. Only a few species in the twenty-one genera under study are shared between neighbouring mountains which can be explained in all cases by a Pleistocene lowering of the montane habitat by 850 m. Therefore a montane forest cover connecting the mountains at colder times as suggested by the pluvial theory can be refuted which is in correspondence with palynological findings suggesting a dry corridor between the mountains. No montane refuge for flightless insects can be identified, because the most species-rich mountain of a genus differs among the genera under study. Instead, each mountain served as a species refuge with a stable habitat. The requirement of a smaller habitat compared to vertebrates is indicated by endemic species on each single mountain suggesting pre-Pleistocene speciation which results even in endemic genera to one mountain. Different small patches of suitable habitat on one mountain could also explain the radiations found in some genera of flightless insects. In some genera species are lacking on Mt Kenya which indicates—with the findings of no endemic passerine bird on the mountain—a probably very dry condition during colder times. On Mt Cameroon no species of the flightless insect genera occurring on the Eastern mountains are found. This contrasts with the existing patterns of birds, grasses and butterflies.     

Establishing a baseline of plant diversity and endemism on a neotropical mountain summit for future comparative studies assessing upward migration: an approach from biogeography and nature conservation

Climate change is forcing many plant species to shift their range in search of adequate environmental conditions, being localized endemic species particularly at risk on mountain summits. The Pantepui biogeographic province, a set of flat-topped mountain summits (called tepuis) of northern South America, contains both high plant diversity and a high degree of endemism. Previous studies based on warming projections for the area suggested that half of the Pantepui endemic flora would disappear due to habitat loss by 2100. In this study, we selected one of the best-explored tepuis, Roraima-tepui, to establish the baseline of diversity and endemism for comparisons with historical data and future monitoring surveys, aimed at testing the hypothesis of upward migration of plants in response to global warming. We also analysed floristic and physiognomic features of the Eastern Tepui Chain (ETC, the mountain range where Roraima is located), and the phytogeographic patterns of both the ETC and Pantepui. The Roraima summit contains 227 species, including 44 new records, 13 exotic species (some of them with high invasive potential), and at least one species new to science. At the ETC level, Roraima is the tepui with highest species richness and degree of endemism, and shows a relatively high floristic similarity with Kukenán and Ilú. Herbaceous species dominate over shrubs on these tepuis, Tramen and Maringma, whereas on Yuruaní, Karaurín and Uei, they reach similar abundances. At the Pantepui level, endemic species have highly localized distribution patterns (17% local endemics). Conservation opportunities are evaluated in light of these results.     

Forest eternal? Endemic butterflies of the Bamenda highlands,Cameroon, avoid close‐canopy forest

The Gulf of Guinea Highlands, a centre of endemism and high conservation importance, represent the only large mountain system in West and Central Africa. We studied habitat use of three common endemic butterflies Colias electo manengoubensis, Bicyclus anisops and Mylothris jacksoni knutsoni, using time‐standardized surveys in four distinct habitats: close‐canopy forest, scrub and forest edges, bracken and grasslands. All three species avoided close‐canopy forests and bracken; the Colias preferring grassland, whereas Bicyclus and Mylothris scrub and forest edges. Ordination analyses of surrounding habitats indicated that all three taxa required heterogeneous landscape mosaics. We argue that the life history traits of taxa with limited geographic distribution may reflect past habitat conditions within their ranges, and that these habitat preferences can indicate the continuous existence of mosaic of forest and nonforest habitats in the West African mountains. Such a landscape was probably maintained by climatic fluctuation and large herbivores, further modified by human impact. This conclusion is consistent with the palaeoenvironmental record and with the requirements of Afromontane endemics from other groups. Recent conservation activities focus on patches of continuous forests, but the mosaic landscapes are no less threatened by intensive agriculture, and should be included to protected areas.     

Spatial heterogeneity of climate change in an Afromontane centre of endemism

Broad‐scale assessments of how climate change might impact mountain ecosystems, especially in areas of high biodiversity and endemism, are compromised by the lack of localised climate feedback in global circulation models. Here, we use regionally downscaled climate models to highlight how spatial variation in forecast change could impact rare plant distributions differentially across the Eastern Arc Mountains of Tanzania and Kenya, part of the Eastern Afromontane Biodiversity Hotspot. Concordant with the theory that climatic stability facilitates the accumulation of rare species, we find significant positive correlations between endemic plant richness and future climatic persistence within the dispersal‐limiting sky islands of this mountain archipelago. Further, we explore the hypothesis that mountain plants will move upslope in response to climate change and find that, conversely, some species are predicted to tend downslope, despite warmer annual conditions, driven by changes in seasonality and water availability. Importantly, two thirds of the modelled plant species are predicted to respond in different directions in different parts of their ranges, exemplifying the potential for individualistic responses of species and disjunct populations to environmental change, and the need for regional focus in climate change impact assessment. Conservation planners, and more broadly those charged with developing climate adaption policy, are advised to take caution in inferring local patterns of change from zoomed perspectives of broad‐scale models. Moreover, a preoccupation with mean annual temperature as the principal driver of ecosystem change is misguided and could compromise efforts to make conservation plans resilient to future climate change. Faced with spatially complex and inherently uncertain future conditions, sensible priorities are to restore forest connectivity and to underpin adaption strategies with knowledge of how ecosystems and people have adapted to previous episodes of rapid change.     

Seasonal elevational movements of Eastern Olive Sunbird Cyanomitra olivacea in the Uluguru Mountains,Tanzania

Little is known about the seasonal elevational movements for most tropical avifauna species. Seasonal elevational movements of the Eastern Olive Sunbird Cyanomitra olivacea were studied along an elevational gradient from 600 to 1 500?m above sea level in the Uluguru Mountains, Tanzania, between May 2005 and February 2006. The recapture of ringed individuals along an elevational gradient across seasons provided evidence for the seasonal elevational movement of the Eastern Olive Sunbird in the Uluguru Mountains and the first documented evidence for this species in the Eastern Arc Mountains as a whole. Due to forest fragmentation and lack of corridors connecting high- and low-altitude forests in the Uluguru Mountains, the results have implications for conservation of the forest along the entire elevational gradient as well as for other forest bird species that have been documented to make seasonal elevational movements in the Uluguru Mountains and the entire Eastern Arc Mountains.     

Speciation mirrors geomorphology and palaeoclimatic history in African laminate-toothed rats (Muridae: Otomyini) of the Otomys denti and Otomys lacustris species-complexes in the 'Montane Circle' of East Africa

We adopted an integrated systematic approach to delimit evolutionary species and describe phylogeographic, morphometric and ecological relationships in Otomys denti (from the Albertine Rift, Southern Rift in Malawi and the northern Eastern Arc Mountains) and Otomys lacustris (from the Southern Rift in Tanzania and Zambia, and the southern Eastern Arc Mountains). Molecular [cytochrome (cyt) b sequences, 1143 bp, N  = 18], craniometric (classical, N  = 100 and geometric, N  = 60) and ecological (Partial Least Squares regression of shape and ecogeographic variables) approaches show a profound, parallel disjunction between two groups: (1) Eastern Arc and Southern Rift (including the Malawi Rift) ( O. lacustris and Otomys denti sungae ) and (2) Albertine Rift ( Otomys denti denti and Otomys denti kempi ) taxa. Within both groups, cyt b sequences or craniometric analysis provided evidence for the differentiation of both southern and northern Eastern Arc from Southern Rift lineages (across the so-called Makambako Gap). Within the Albertine Rift ( denti – kempi ) lineage, populations from individual mountain ranges differed significantly in skull shape (but not size), but were similar genetically. Over-reliance in the past on very few morphological characters (e.g. number of molar laminae) and a polytypic species concept has obscured phylogenetic relationships and species discrimination in this group. We recognize at least three species in this group, and distinct lineages within two of these species. Each species or lineage was endemic to one of three regions: the Albertine Rift, the Malawi Rift or the Eastern Arc. Our result echo conclusions of recent studies of other mammalian and bird taxa and reflect the geomorphology and palaeoclimatic history of the region.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 913–941.     

Assessment of the impact of the Lower Kihansi Hydropower Project on the forests of Kihansi Gorge, Tanzania

Construction of a hydropower project on the Kihansi river in Southern Tanzania will substantially alter the river's flow. On the basis of both qualitative and quantitative botanical surveys, forest in the Kihansi gorge below the dam site was found to be mostly typical species and endemic-rich Eastern Arc forest. An unusual forest type, dominated almost entirely by Filicium decipiens was also present. Eastern Arc forests are of both global and national importance for biodiversity conservation, and measures to mitigate impact of the dam on the forest are suggested. Further environmental monitoring is recommended in order to evaluate the choice of mitigation measures.     

Herpetofaunal Richness and Community Structure of Offshore Islands of Sulawesi,Indonesia1

We examined the distribution and broad habitat associations of the herpetofauna on three offshore islands of southeast Sulawesi, Indonesia. A total of 74 amphibian and reptile taxa were recorded, comprising 13 frogs, 29 lizards, 29 snakes, 1 freshwater turtle, and 1 crocodile. Of the total taxa, 38 percent were endemic to Sulawesi, 13 were new undescribed taxa. Range extensions were also recorded for one taxon previously not known from Sulawesi. Herpetofauna of these islands is largely derived from that of mainland Sulawesi, and as for Sulawesi generally, is depauperate compared with herpetofaunal assemblages in Borneo, Java, and Thailand. Taxon richness was much higher in minimally disturbed forest and forest habitats with only moderate disturbance levels than in highly modified or disturbed habitats, such as secondary forests, plantations, and villages. Disturbed habitats were characterized by widespread, habitat generalists and human commensals. Forests were characterized by endemic and habitat‐specialist taxa. Little discrimination of taxon composition or endemism was found between minimally and moderately disturbed forest habitats. These results reaffirm the need for more general biological survey and research in this region. Taxa most likely to be displaced by human impacts tend to be endemic taxa, for which there exists little or no ecological information. The similarity in the herpetofaunal community structure between habitats with minimal and moderate disturbance levels has important implications for our understanding of ecological resilience in tropical herpetofaunal communities.     

Integrating the Rabinowitz rarity framework with a National Plant Inventory in South Korea

Increasingly large presence‐only survey datasets are becoming available for use in conservation assessments. Potentially, these records could be used to determine spatial patterns of plant species rarity and endemism. We test the integration of a large South Korean species record database with Rabinowitz rarity classes. Rabinowitz proposed seven classes of species rarity using three variables: geographic range, habitat specificity, and local population size. We estimated the range size and local abundance of 2,215 plant species from species occurrence records and habitat specificity as the number of landcover types each species’ records were found in. We classified each species into a rarity class or as common, compared species composition by class to national lists, and mapped the spatial pattern of species richness for each rarity class. Species were classed to narrow or wide geographic ranges using 315 km, the average from a range size index of all species (D_max), based on maximum distance between observations. There were four classes each within the narrow and wide range groups, sorted using cutoffs of local abundance and habitat specificity. Nationally listed endangered species only appeared in the narrow‐range classes, while nationally listed endemic species appeared in almost all classes. Species richness in most rarity classes was high in northeastern South Korea especially for species with narrow ranges. Policy implications. Large presence‐only surveys may be able to estimate some classes of rarity better than others, but modification to include estimates of local abundance and habitat types, could greatly increase their utility. Application of the Rabinowitz rarity framework to such surveys can extend their utility beyond species distribution models and can identify areas that need further surveys and for conservation priority. Future studies should be aware of the subjectivity of the rarity classification and that regional scale implementations of the framework may differ.     

Unusual abundance–range size relationship in an Afromontane bird community: the effect of geographical isolation?

Aim To show that the frequently reported positive trend in the abundance–range‐size relationship does not hold true within a montane bird community of Afrotropical highlands; to test possible explanations of the extraordinary shape of this relationship; and to discuss the influence of island effects on patterns of bird abundance in the Cameroon Mountains. Location Bamenda Highlands, Cameroon, Western Africa. Methods We censused birds during the breeding season in November and December 2003 using a point‐count method and mapped habitat structure at these census points. Local habitat requirements of each species detected by point counts were quantified using canonical correspondence analysis, and the size of geographical ranges of species was measured from their distribution maps for sub‐Saharan Africa. We tested differences in abundance, niche breadth and niche position between three species groups: endemic bird species of the Cameroon Mountains, non‐endemic Afromontane species, and widespread species. Results We detected neither a positive nor negative abundance–range‐size relationship in the bird community studied. This pattern was caused by the similar abundance of widespread, endemic and non‐endemic montane bird species. Moreover, endemic and non‐endemic montane species had broader local niches than widespread species. The widespread species also used more atypical habitats, as indicated by the slightly larger values of their niche positions. Main conclusions The relationship detected between abundance and range size does not correspond with that inferred from contemporary macroecological theory. We suggest that island effects are responsible for the observed pattern. Relatively high abundances of montane species are probably caused by their adaptation to local environmental conditions, which was enabled by climatic stability and the isolation of montane forest in the Cameroon Mountains. Such a unique environment provides a less suitable habitat for widespread species. Montane species, which are abundant at present, may also have had large ranges in glacial periods, but their post‐glacial distribution may have become restricted after the retreat of the montane forest. On the basis of comparison of our results with studies describing the abundance structure of bird communities in other montane areas in the Afrotropics, we suggest that the detected patterns may be universal throughout Afromontane forests.     

Distribution of endemic and threatened herpetofauna in Mt. Malindang,Mindanao, Philippines

Mt. Malindang is one of the upland ranges where biodiversity has been severely threatened due to forest loss. Fieldwork was conducted from October 2003 to December 2004 in 14 sampling sites from an elevation of 120 to over 1,700 m above sea level to assess the distribution of endemic and threatened herpetofaunal species. Twenty-six species of amphibians and 33 species of reptiles were observed for all sampling sites. The level of endemism for amphibians was 42% where 7 of the 11 recorded species are found only in Mindanao. Nine species were in the threatened category, 8 vulnerable and 1 endangered. For the reptiles, 48% endemicity was observed. No threatened species was found. Field observations show that the major threat to the herpetofauna is habitat destruction, particularly the conversion of the forest to agricultural farms by the local people. It was also observed that endemic and threatened species were distributed in high elevation sites (submontane, dipterocarp, almaciga, and montane forests). Despite habitat loss in Mt. Malindang, 18% of the recorded herpetofaunal species recorded in the Philippines were found in Mt. Malindang, indicating the conservation importance of this mountain range.     

Seasonal variation in diversity and abundance of understorey birds in Bunduki Forest Reserve,Tanzania: evaluating the conservation value of a plantation forest

Plantation forests generally support lower bird diversity than natural forests. However, in some instances the plantations have been found to provide suitable habitat for a number of bird species. In the Eastern Arc Mountains, there is limited knowledge how understorey birds, some of which make seasonal altitudinal movements, use plantations. Using mist netting we assessed seasonal use of the plantation forest by the understorey bird community in Bunduki Forest Reserve in the Uluguru Mountains. Species diversity and capture rates were significantly higher during the cold season than during the hot season possibly due to seasonal altitudinal migration by some species. The use of plantations by those species that make seasonal altitudinal movements shows that plantation forests can enhance indigenous biodiversity by enabling connectivity between two or more natural forest patches. Our findings suggest that in a situation where there is no natural forest, an exotic plantation with suitable indigenous understorey cover can help in protection of birds, including endemic and near-endemic species.     

Elevational zonation of afrotropical forest bird communities along a homogeneous forest gradient

Aim This study analyses the distribution and abundance of birds from a forested tropical gradient in order to determine whether elevationally distinct communities are detectable in this habitat. Location An avifaunal census was carried out on a single transect within the tropical forest of the Udzungwa Mountains in the Eastern Arc, Tanzania, covering a range in elevation from 300 to 1850 m. Methods Two complementary data sets on forest birds were analysed, encompassing (1) data derived from standardized 20‐ha spot‐mapping censuses performed at nine elevations over 175‐m intervals from 400 to 1800 m a.s.l., and (2) all observations of birds binned into 32 data points at 50‐m intervals, from 300 to 1850 m a.s.l. The degree of zonation in the avian community along the elevational gradient was examined using the chronological clustering method, an agglomerative hierarchical clustering method that can be carried out with a range of similarity indices. Results The chronological clustering analysis of the data set based on standardized spot‐mapping revealed a clearly defined boundary at c. 1200 m a.s.l., separating lowland from montane communities. Most bird species could be categorized as belonging to one of these two communities. The data set based on all observations revealed a number of potential secondary boundaries, although these boundaries delimited the entire elevational ranges of individual species in only relatively few cases. Main conclusions In contrast to previously published studies, we find evidence of an elevational zonation of distinct communities within a seemingly homogeneous habitat. Although similar boundaries have been assumed to arise as a result of vegetational ecotones, or because of interspecific competition, these mechanisms are poorly corroborated. We suggest that the causes of patterns of zonation are not well understood, and that the interplay among species distributions, species richness, and environmental factors needs more consideration. The chronological clustering method is proposed as an appropriate tool for studying these specific patterns.