Biodiversity Indicator Groups of Tropical Land‐use Systems: Comparing Plants, Birds, and Insects

Abstract

Tropical landscapes are dominated by land‐use systems, but their contribution to the conservation of biodiversity is largely unknown. Since changes in biodiversity in response to human impact are known to differ widely among taxonomic groups and guilds, there is a need for multidisciplinary collaboration of plant, vertebrate, and invertebrate experts. We used inventories of trees, understory plants, birds (subdivided into endemics, insectivores, frugivores/nectar feeders), butterflies (endemics, fruit feeders), and dung beetles in Sulawesi (Indonesia) to characterize a gradient from near‐primary to secondary forests, agroforestry systems, and annual crops. As expected, overall species richness tended to decrease within this gradient of increasing habitat modification, but, in contrast to previous studies, we found the species richness between most taxonomic groups to be significantly correlated (36 out of 38 pairwise comparisons). However, on average only 48% of the variance could be explained (within the five main groups), and only a few taxonomic groups/guilds turned out to be good predictors for others: for example, trees for fruit‐ and nectar‐feeding birds (88% explanation) and fruit‐feeding butterflies (83%), endemic birds for endemic butterflies (72%), and frugivorous/nectar‐feeding birds for fruit‐feeding butterflies (67%). Although biodiversity of land‐use systems showed taxonomic group‐ and guild‐specific differences, most groups were affected in a similar way by habitat modification. Near‐primary forest sites proved to be of principal importance for conservation; however, land‐use systems such as secondary forests (for understory plants, birds, and butterflies) and agroforestry systems (for butterflies) supported relatively high numbers of species and might play a significant role for biodiversity conservation in tropical landscapes.

Tradeoffs between income, biodiversity, and ecosystem functioning during tropical rainforest conversion and agroforestry intensification

“…Only forest-based trees, herbs, and canopy ants tended to decline with shade cover reduction, whereas species richness of other groups, both forestand non-forest-based species, remained constant. Other studies have reported a significant reduction in biodiversity along land-use intensification gradients in the tropics (5,6,19,20,25). This discrepancy is likely due to different extents in the analyzed land use gradients, with most studies also including agricultural systems completely devoid of trees.…”

“…The transition from forest to cacao agroforestry resulted in a loss of Ϸ60% of the forest-based species with plant species being more strongly affected than mobile insect taxa. It seems reasonable to assume that rare, specialized, and endangered species are represented disproportionately high in this fraction (6), underlining the limitations of agroforestry for conservation of forest species (16). Unfortunately, detailed distributional and ecological data are lacking on most species encountered.…”

“…Developing strategies to reconcile human needs with the integrity of our environment is a major task for ecologists and socio-economists alike (4), but multitaxa studies are rare (5)(6) and too little is known about the human dimension of land use changes (4,(7)(8)(9)(10)(11) and consequences for ecosystem functioning (1,2,(12)(13)(14). Furthermore, most ecological and economic studies on ecosystem services are carried out separately so that information cannot be brought together (15).…”

“…For comparison, open cacao plantations without shade trees were included in socioeconomic studies. As biological indicator taxa, we used plants and insects because they represent Ϸ80% of all described species and determine important ecosystem processes (6,(12)(13)(14). To relate ecological changes to socioeconomic parameters, we used percent canopy cover as an indicator of forest tree loss and agroforestry intensification (17,(19)(20).…”

Plant functional types and traits as biodiversity indicators for tropical forests: two biogeographically separated case studies including birds, mammals and termites

“…Candidate indicators such as landscape metrics, remotely-sensed variables, multi-species indices and formulated measures of ecosystem complexity or genetic diversity have found wide application but are of limited practicality in forests (UNEP-CBD 1996; Kapos et al 2001;Delbaere 2002; European Academies' Science Advisory Council (ESAC) 2004; Gregory et al 2005;Duraiappah and Naeem 2005). Thus forest biodiversity surveys still maintain a taxonomic focus even though the costs of obtaining sufficient sampling can be high and the utility of any one species, or another single taxon, as a predictor of others remains uncertain (Lawton et al 1998;Watt et al 1998;Dufrêne and Legendre 1997;UNEP/CBD 2003;Gregory et al 2005, but see also Schulze et al 2004). Further, at large spatial scales where within-region diversity is large, higher level taxa (up to family level) must often be used (Villaseñor et al 2005), but even this is only justifiable where extensive species data are already available (Sarkar et al 2005).…”