Forest Fragmentation and Selective Logging Have Inconsistent Effects on Multiple Animal-Mediated Ecosystem Processes in a Tropical Forest

Abstract

Forest fragmentation and selective logging are two main drivers of global environmental change and modify biodiversity and environmental conditions in many tropical forests. The consequences of these changes for the functioning of tropical forest ecosystems have rarely been explored in a comprehensive approach. In a Kenyan rainforest, we studied six animal-mediated ecosystem processes and recorded species richness and community composition of all animal taxa involved in these processes. We used linear models and a formal meta-analysis to test whether forest fragmentation and selective logging affected ecosystem processes and biodiversity and used structural equation models to disentangle direct from biodiversity-related indirect effects of human disturbance on multiple ecosystem processes. Fragmentation increased decomposition and reduced antbird predation, while selective logging consistently increased pollination, seed dispersal and army-ant raiding. Fragmentation modified species richness or community composition of five taxa, whereas selective logging did not affect any component of biodiversity. Changes in the abundance of functionally important species were related to lower predation by antbirds and higher decomposition rates in small forest fragments. The positive effects of selective logging on bee pollination, bird seed dispersal and army-ant raiding were direct, i.e. not related to changes in biodiversity, and were probably due to behavioural changes of these highly mobile animal taxa. We conclude that animal-mediated ecosystem processes respond in distinct ways to different types of human disturbance in Kakamega Forest. Our findings suggest that forest fragmentation affects ecosystem processes indirectly by changes in biodiversity, whereas selective logging influences processes directly by modifying local environmental conditions and resource distributions. The positive to neutral effects of selective logging on ecosystem processes show that the functionality of tropical forests can be maintained in moderately disturbed forest fragments. Conservation concepts for tropical forests should thus include not only remaining pristine forests but also functionally viable forest remnants.

Species richness matters for the quality of ecosystem services: a test using seed dispersal by frugivorous birds

“…These results are similar to those found in other animal-derived services across disturbed landscapes (e.g. pollination; [14]), but contrast with previous research which has failed to detect frugivore richness effects on frugivory or seed dispersal magnitude [37,39,40]. Moreover, as far as we know, our study is the first to suggest a positive effect of frugivore diversity in the probability of tree colonization outside forest boundaries, as the degree of seed deposition in open microsites, although less predictable than the other dispersal components, was exclusively driven by frugivore richness.…”

“…We surmise these findings to be generalized to many trophicderived services whose quality is expected to be driven by the degree of functional heterogeneity among animal species (e.g. pollination, biological control and detritivory [40,44]). …”

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…In general, studies that account for fragmentation on different spatial scales are rare (but see Garcia and Chacoff, 2007;Schleuning et al, 2011b;Stephens et al, 2003). Forest fragmentation (large-scale reduction of fragment size) can affect ecosystem processes indirectly by changes in biodiversity, whereas selective logging (local scale) influenced ecosystem processes (e.g.…”

Mating patterns and pollinator mobility are critical traits in forest fragmentation genetics

“…Fragmentation causes the spatial arrangement of plants to change (Young et al, 1996;Aguilar et al, 2008) and may change the abundance and foraging behaviour of pollinators (Schleuning et al, 2011;Hadley and Betts, 2012). However, populations of animalpollinated woody plants do not appear to be as susceptible as many other taxa to the small population paradigm effects resulting from habitat fragmentation (for example, genetic drift), which dominate conservation genetics-the 'paradox of forest fragmentation genetics' (Kramer et al, 2008;Vranckx et al, 2011).…”