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Abstract In their natural West African rainforest habitat, Diana monkeys continuously produce high rates of a close-range clear-sounding call, but the function of this behaviour is unknown. In other primate species, close-range calls are typically given in socially relevant situations, for example, to gain access to grooming partners or food. Quite contrarily, we tested a number of hypotheses and found that Diana monkey 'clear' calls primarily function to avoid predation. Call rates were significantly elevated when predation threat was high, for instance when the visibility was poor, when the group spread was large, when the group was not associated with other monkey species, or after alarm calls. Call rates were not significantly elevated, however, in circumstances of high social competition, for instance when the group spread was small, during resting phases, while feeding on clumped food sources, or when foraging in the periphery where inter-group encounters were more likely to occur. Calling was contagious in that calls typically elicited vocal responses from out-of-sight group members within a few seconds. Because of this, callers can effectively monitor a much larger area than is visually accessible to single individuals, suggesting that Diana monkey clear calls act as an essential element in a mutualistic system of co-ordinated vigilance.

Interactions of biotic and abiotic factors are critical in determining population dynamics and maintenance of high diversity in tropical rainforests. An investigation was conducted to test the hypothesis that tree species composition and dispersion influence spatial pattern of soil properties on a small scale of meters. Soil variables (pH, EC and total and water extractable (available) K, Ca, Mg and Mn) were highly heterogeneous in both vertical and horizontal dimensions. Available Mn was the most variable (coefficient of variation CV = 76%) parameter and pH the least (CV = 4%). There was an inverse relationship between abundant levels of available cations and heterogeneity. Plots with high heterogeneity in available cations had low tree diversity but there was no evident pattern between total concentration of cations and tree diversity. Tree diversity was negatively correlated to variability of available Mn (r = −0.7). These findings indicate that tree diversity influences soil heterogeneity hence contributing to maintenance of high diversity in tropical rainforests. The results show that the observed soil patterns are caused by geogenic processes as well as processes influenced by vegetation. The raising effect of the vegetation on the elements is expected in the order from Mn, Ca, Mg to K. This vegetation effect indicates the significance of maintaining a closed canopy in tropical rain forests. Geodiversity is thus correlated to biodiversity and needs to be more recognized in ecological research.

To counteract an increasing biodiversity decline, parks and protected areas have been established worldwide. However, many parks lack adequate management to address environmental degradation. To improve management strategies simple tools are needed for an assessment of human impact and management effectiveness of protected areas. This study quantifies the current threats in the heavily fragmented and degraded tropical rainforest of Kakamega, western Kenya. We recorded seven disturbance parameters at 22 sites in differently managed and protected areas of Kakamega Forest. Our data indicate a high level of human impact throughout the forest with illegal logging being most widespread. Furthermore, logging levels appear to reflect management history and effectiveness. From 1933 to 1986, Kakamega Forest was under management by the Forest Department and the number of trees logged more than 20 years ago was equally high at all sites. Since 1986, management of Kakamega Forest has been under two different organizations, i.e. Forest Department and Kenya Wildlife Service. The number of trees logged illegally in the last 20 years was significantly lower at sites managed by the Kenya Wildlife Service. Finally, logging was lower within highly protected National and Nature Reserves as compared to high logging within the less protected Forest Reserves. Reflecting management effectiveness as well as protection status in Kakamega Forest, logging might therefore provide a valuable quantitative indicator for human disturbance and thus an important tool for conservation managers. Logging might be a valuable indicator for other protected areas, too, however, other human impact such as e.g. hunting might also prove to be a potential indicator.