Ecology of Foliicolous Lichens at the “Botarrama” Trail (Costa Rica), a Neotropical Rain Forest. I. Species Composition and its Ecogeographical Implications1

A total of 217 species of typically foliicolous lichens were found at the “Botarrama” trail, a premontane rain forest in the Braulio Carrillo National Park, Costa Rica. The species composition confirmed the classification of this study sice as transitional between lowland wet and montane rain forest. In terms of species tichness, the foliicolous lichen flora was dominated by the families Gomphillaceae (Calenia, Echinoplaca, Gyalideopsis, and Tricharia), Trichotheliaceae (Porina and Tricbothelium), and Pilocarpaceae (Byssoloma and Fellhanera). The most frequent species were Porina mirabilis (including its supposed anamorph Phyllophiale alba), Gyalectidium filicinum, Porina rufula, and Strigula platypoda. A large proportion of the species was rare. Frequency distributions based on area cover corresponded well to general community models by closely fitting a log-normal approximation. Half of the species had narrow ecological amplitudes while more than 70 percent exhibited a wide geographical distribution, thus making che study site representative of a Neotropical rain forest. The use of foliicolous lichens as indicators of altitudinal zonation is discussed.     

Fragmented living: Behavioural ecology of primates in a forest fragment in the Lopé Reserve, Gabon

A 17-month study was made of the primates using a 9-ha “island” of forest, surrounded by savanna, in the northern part of the Lopé Reserve, Gabon. One group ofCercopithecus cephus (plus a young maleCercopithecus nictitans who was in permanent association with them) were resident in the fragment and groups of five other species of primates made visits during 127 days of observation:Pan troglodytes, 15 visits;Cercocebus albigena, 10;Colobus satanas, 3;Cercopithecus nictitans, 2;C. pogonias, 1. Visits were also made by lone males of three species,C. nictitans, Cercocebus albigena, andMandrillus sphinx. The eighth species of diurnal primate present at Lopé,Gorilla g. gorilla, did not visit the fragment during the study. Compared to conspecific groups in neighbouring continuous forest, primates in the fragment ate less fruit, seeds and flowers and more insects and leaves. The local population density of primates resident in the fragment was equivalent to that of the neighbouring continuous forest where all eight species occur, despite the diversity and abundance of fruit being less in the fragment. The costs imposed on the resident group by the reduced diversity and availability of preferred fruit foods appeared to be offset by a number of benefits that increased individual feeding efficiency for monkeys residing within a single fragment. These included lower travel costs, reduced feeding competition between individuals through group fission, and excellent knowledge of the location and quality of food resources in the small home range. It is also possible that the overall negative impact of inter-specific feeding competition was lower in fragments than in continuous forest and that micro-habitat differences resulted in an increased availability of palatable insect and leaf fallback foods in the fragment.     

Predicting community characteristics from habitat conditions: fluvial fish and hydraulics

1. One current approach to the prediction of community characteristics is to use models of key local-scale processes (e.g. niche dimensions) affecting individuals and to estimate the effects of these attributes over larger scales. We tested this approach, focusing on how the hydraulic habitat structures fluvial fish communities. 2. We used a recent statistical habitat model to predict fish community characteristics in eleven reaches in the Rhône river basin in France. Predictions were made ‘blindly’ since most reaches were not used to calibrate the model. The model reflects species preferences for local hydraulics. We made predictions of the fish community from the local hydraulic conditions found in the reaches under low flow conditions. The overall abundance and the relative abundance (both as indices) of fish species, specific size classes and species traits (i.e. reproductive, trophic, morphological and others) were predicted. We summarized our predictions of the relative abundance of species as two ‘community structure indices’ using Principal Component Analysis. 3. Our predictions from low-flow hydraulics were compared with long-term observations of fish communities. The relative abundance of species actually observed depended largely on zoogeographic factors within the Rhône basin which could not be predicted by the model. The model predicted 13% of the variance in the indices of relative abundance at the species level and 23% of this variance at the trait level for all zoogeographic regions combined. However, when focused on reaches within a geographic region, the model explained up to 47% of the same variance. Therefore, geographic regions act as ‘filters’ on the relative abundance of species, but hydraulics do affect fish communities within a given geographical context. 4. For the synthetic ‘community structure indices’, we obtained good predictions from hydraulics independently of the geographical context (variance explained up to 95%). These indices were linked to simple key hydraulic characteristics of river reaches (Froude and/or Reynolds number). The indices enabled interpretations of the links between hydraulics, geomorphology, discharge and community patterns. These links were consistent with existing knowledge of species and their traits. 5. In addition to the above validations, the habitat model partly explained the observed effects of impoundment on fish communities. 6. The present results show that stream hydraulics strongly impact fish community structure. Consequently, our findings confirm that community characteristics can be predicted using models of the local-scale habitat requirements of the species forming the community.