Landscape modification and habitat fragmentation are key drivers of global species loss. Their effects may be understood by focusing on: (1) individual species and the processes threatening them, and (2) human-perceived landscape patterns and their correlation with species and assemblages. Individual species may decline as a result of interacting exogenous and endogenous threats, including habitat loss, habitat degradation, habitat isolation, changes in the biology, behaviour, and interactions of species, as well as additional, stochastic threats. Human-perceived landscape patterns that are frequently correlated with species assemblages include the amount and structure of native vegetation, the prevalence of anthropogenic edges, the degree of landscape connectivity, and the structure and heterogeneity of modified areas. Extinction cascades are particularly likely to occur in landscapes with low native vegetation cover, low landscape connectivity, degraded native vegetation and intensive land use in modified areas, especially if keystone species or entire functional groups of species are lost. This review (1) demonstrates that species-oriented and pattern-oriented approaches to understanding the ecology of modified landscapes are highly complementary, (2) clarifies the links between a wide range of interconnected themes, and (3) provides clear and consistent terminology. Tangible research and management priorities are outlined that are likely to benefit the conservation of native species in modified landscapes around the world.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1466-8238.2007.00287.x

Landscape modification and habitat fragmentation: a synthesis

A review of the literature shows that in nearly all cases tropical rain forest fragmentation has led to a local loss of species. Isolated fragments suffer reductions in species richness with time after excision from continuous forest, and small fragments often have fewer species recorded for the same effort of observation than large fragments or areas of continuous forest. Birds have been the most frequently studied taxonomic group with respect to the effects of tropical forest fragmentation. The mechanisms of fragmentation-related extinction include the deleterious effects of human disturbance during and after deforestation, the reduction of population sizes, the reduction of immigration rates, forest edge effects, changes in community structure (second- and higher-order effects) and the immigration of exotic species. The relative importance of these mechanisms remains obscure. Animals that are large, sparsely or patchily distributed, or very specialized and intolerant of the vegetation surrounding fragments, are particularly prone to local extinction. The large number of indigenous species that are very sparsely distributed and intolerant of conditions outside the forest make evergreen tropical rain forest particularly susceptible to species loss through fragmentation. Much more research is needed to study what is probably the major threat to global biodiversity.

Species loss in fragments of tropical rain forest: a review of the evidence.

The survival of primates in moderately disturbed forests is determined by a complex of variables. Correlation analyses suggest that ecological features of a species may confer a basal survival ability but that details of the form of disturbance may be crucially important. Correlation analyses reveal that body size alone is a poor predictor of primate response to moderate forest disturbance. However, when the effects of diet variables are held constant, body size more strongly correlates with survival ability (smaller species surviving better). Degree of frugivory shows a significant negative correlation with survival ability at both univariate and multivariate levels of analysis. In contrast, dietetic diversity is not correlated with survival ability at either level of analysis. Together, body size and percentage frugivory explain 44% of the variation in species’ responses to moderate habitat disturbance. Idiosyncratic responses of species can usually be traced to specific features of the changing environment, such as selective elimination of important food sources and, conversely, the presence of increased densities of particular food sources arising from the disturbance.

Responses of rain-forest primates to habitat disturbance: A review

It has long been thought that predation has had important ecological and evolutionary effects on primates as prey. Predation has been theorized to have been a major selective force in the evolution of hominids.1 In modern primates, behaviors such as active defense, concealment, vigilance, flight, and alarm calls have been attributed to the selective pressures of predation, as has group living itself. It is clear that primates, like other animals, have evolved ways to minimize their risk of predation. However, the extent to which they have been able to do so, given other constraints of living such as their own need to acquire food, has not yet been resolved. Perhaps most hotly debated is whether predation has been the primary selective force favoring the evolution of group living in primates. Part of the difficulty in resolving the debate lies in a paucity of direct evidence of predation. This is regrettable yet understandable since primatologists, by definition, focus on the study of primates, not predators of primates (unless these are also primates). Systematic direct evidence of the effects of predation can best be obtained by studying predators that are as habituated to observers as are their primate prey. Until this is done, we must continue to rely on opportunistic accounts of predation and predation attempts, and on systematically obtained indirect evidence. Such data reveal several interesting patterns: (1) although smaller primates may have greater predation rates than larger primates, even the largest primates are not invulnerable to predation; (2) the use by primates of unfamiliar areas can result in higher predation rates, which might be one pressure favoring philopatry, or site fidelity; (3) arboreal primates are at greater risk of predation when they are more exposed (at forest edges and tops of canopies) than in more concealed locations; (4) predation by mammalian carnivores may often be episodic; and (5) terrestrial primates may not experience greater predation than arboreal primates.

Predation on primates: Ecological patterns and evolutionary consequences

Tropical forests and the animals they support are being threatened byaccelerating rates of forest conversion and degradation In a continuallyfluctuating sociopolitical world, it is often impossible to protect areasfrom such conversion until the political environment is suitable to pur-sue conservation goals, by which time, the forests have often been con-verted to other uses This reality suggests a need for inquiry into whichprimate species can persist after different types of disturbances and howquickly primate communities can recover from disturbance Here we ex-amine the persistence of primate populations in disturbed habitats byproviding a case study of patterns of primate abundance in areas of KibaleNational Park (766 km

Habitat alteration and the conservation of African primates: case study of Kibale National Park, Uganda.

Only a small percentage of tropical forests are legally protected and so, if we are to conserve tropical forest species we must encourage sustainable exploitation of unprotected forest areas. Selective timber harvesting is frequently cited as a sustainable use of tropical forests and the authors studied the effects of this kind of exploitation on natural treefall rates, an important regulative process, in the Kibale Forest, Uganda. Their results indicate that levels of destruction typical of capital intensive mechanised timber harvesting seriously disrupt the dynamic balance of the forest. They discuss alternative methods for selective timber harvesting that would be less disruptive and present an objective method which may help rain forest managers determine which multiple-use options are compatible with rain forest conservation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0030605300018779

Tropical forest management: can rates of natural treefalls help guide us?

Crowned Eagles Strephanoaetus coronatus in rainforest: observations on breeding chronology and diet at a nest in Uganda

The rate at which social groups of primates are encountered in disturbed rain forest may be biased relative to undisturbed rain forest. A recently reported case study revealed a 25% reduction in postlogging raw encounter rates even though the true density of primates remained at the prelogging level. If biased raw encounter rates are typical of disturbed forests, and if they translate into equally biased line-transect density estimates, results of many comparative surveys might prove misleading (ie, apparent declines of primates in disturbed forest may not be real). Here a set of line-transect density estimates from logged forest are tested for systematic bias by comparing them to range-mapping density estimates, and the response of a Fourier series detectability function to several hypothetical patterns of bias in raw encounter rates is illustrated. Tests of line-transect density estimates from logged forest provide no evidence of systematic bias. The Fourier series results suggest that biased raw encounter rates may often be ameliorated by line-transect density estimators. Available evidence suggests that line-transect density estimates or similarly transformed encounter rates usually provide reliable comparative results within the limits of a particular study's resolution. In contrast, conclusions drawn directly from comparative raw encounter rates (without transforming them into density estimates) are more prone to error.

Do line-transect surveys systematically underestimate primate densities in logged forests?

A recently proposed model of competition was claimed to have predicted accurately the independently estimated densities of four sympatric primates in Kibale Forest, Uganda. The validity of one of the key assumptions of the model, the assumption of comparable land tenure systems, is examined here. Results show that when deviation from the assumption of comparable land tenure systems is accounted for, the model fails to predict Kibale primate densities. Possible reasons for model failure are discussed, and it is concluded that despite model failure when applied to the specific case of Kibale primates, the model remains a valuable heuristic tool.

Joseph P. Skorupa

Papers

Responses of rain-forest primates to habitat disturbance: A review

Tropical forest management: can rates of natural treefalls help guide us?

Crowned Eagles Strephanoaetus coronatus in rainforest: observations on breeding chronology and diet at a nest in Uganda

Do line-transect surveys systematically underestimate primate densities in logged forests?

Monkeys and matrices: a second look.