Aim In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support.

Location  World-wide.

Methods  We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study.

Main conclusions  The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.0305-0270.2003.00994.x

Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures

Species abundance distributions (SADs) follow one of ecologys oldest and most universal laws – every community shows a hollow curve or hyperbolic shape on a histogram with many rare species and just a few common species. Here, we review theoretical, empirical and statistical developments in the study of SADs. Several key points emerge. (i) Literally dozens of models have been proposed to explain the hollow curve. Unfortunately, very few models are ever rejected, primarily because few theories make any predictions beyond the hollow-curve SAD itself. (ii) Interesting work has been performed both empirically and theoretically, which goes beyond the hollow-curve prediction to provide a rich variety of information about how SADs behave. These include the study of SADs along environmental gradients and theories that integrate SADs with other biodiversity patterns. Central to this body of work is an effort to move beyond treating the SAD in isolation and to integrate the SAD into its ecological context to enable making many predictions. (iii) Moving forward will entail understanding how sampling and scale affect SADs and developing statistical tools for describing and comparing SADs. We are optimistic that SADs can provide significant insights into basic and applied ecological science.

/pdf/species-abundance-distributions-moving-beyond-single-4kjxq2isjo.pdf

Species abundance distributions: moving beyond single prediction theories to integration within an ecological framework

Despite concern about the effects of tropical forest disturbance and clearance on biodiversity1,2, data on impacts, particularly on invertebrates, remain scarce3,4,5,6,7,8. Here we report a taxonomically diverse inventory on the impacts of tropical forest modification at one locality. We examined a gradient from near-primary, through old-growth secondary and plantation forests to complete clearance, for eight animal groups (birds, butterflies, flying beetles, canopy beetles, canopy ants, leaf-litter ants, termites and soil nematodes) in the Mbalmayo Forest Reserve, south-central Cameroon. Although species richness generally declined with increasing disturbance, no one group serves as a good indicator taxon9,10,11,12 for changes in the species richness of other groups. Species replacement from site to site (turnover) along the gradient also differs between taxonomic groups. The proportion of ‘morphospecies’ that cannot be assigned to named species and the number of ‘scientist-hours’ required to process samples both increase dramatically for smaller-bodied taxa. Data from these eight groups indicate the huge scale of the biological effort required to provide inventories of tropical diversity, and to measure the impacts of tropical forest modification and clearance.

Biodiversity inventories, indicator taxa and effects of habitat modification in tropical forest

Most tropical forests outside protected areas have been or will be selectively logged so it is essential to maximize the conservation values of partially harvested areas. Here we examine the extent to which these forests sustain timber production, retain species, and conserve carbon stocks. We then describe some improvements in tropical forestry and how their implementation can be promoted. A simple meta-analysis based on >100 publications revealed substantial variability but that: timber yields decline by about 46% after the first harvest but are subsequently sustained at that level; 76% of carbon is retained in once-logged forests; and, 85‐100% of species of mammals, birds, invertebrates, and plants remain after logging. Timber stocks will not regain primary-forest levels within current harvest cycles, but yields increase if collateral damage is reduced and silvicultural treatments are applied. Given that selectively logged forests retain substantial biodiversity, carbon, and timber stocks, this “middle way” between deforestation and total protection deserves more attention from researchers, conservation organizations, and policy-makers. Improvements in forest management are now likely if synergies are enhanced among initiatives to retain forest carbon stocks (REDD+), assure the legality of forest products, certify responsible management, and devolve control over forests to empowered local communities.

/pdf/sustaining-conservation-values-in-selectively-logged-1olkbzv6lh.pdf

Sustaining conservation values in selectively logged tropical forests: the attained and the attainable

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 bee- tles 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 pre- vious studies, we found the species richness between most taxonomic groups to be signif- icantly 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 but- terflies (67%). Although biodiversity of land-use systems showed taxonomic group- and guild-specific differences, most groups were affected in a similar way by habitat modifi- cation. 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.

/pdf/biodiversity-indicator-groups-of-tropical-land-use-systems-3wrszcoa8k.pdf

Biodiversity indicator groups of tropical land‐use systems: comparing plants, birds, and insects

1. The butterfly fauna of lowland monsoon forest on Buru, Indonesia was compared in unlogged forest and forest that had been selectively logged 5 years previously. 2. Seven variables relating to vegetation structure were measured in each habitat. Tree density and percentage cover of vegetation in the canopy and understorey were significantly higher, and vegetation cover 2 m above the ground was significantly lower, in unlogged forest. There were no differences between sites in the mean heights or girths of trees, but the ranges of both heights and girths were lower in logged forest. Percentage cover of vegetation at ground level was similar at the two sites. 3. Species richness, abundance and evenness of butterflies and an index of taxonomic distinctiveness were all significantly higher in unlogged forest. Two endemic species and a further four species with distributions restricted to Maluku Province were recorded only in unlogged forest. 4. Species abundance data for butterflies at both sites fitted a log-series distribution. Data for unlogged forest also fitted a log-normal distribution, whereas those for logged forest did not. This indicated the presence of a more complex butterfly community in unlogged forest. 5. These results indicate that the distributional pattern of species abundance of tropical butterflies may be used as an indicator of forest disturbance, and that selective logging of tropical forests in SE Asia may be associated with a significant decrease in biodiversity of butterflies, at least during the first 5 years of forest regeneration.

Effects of selective logging on tropical forest butterflies on Buru, Indonesia

Butterfly assemblages within lowland monsoon forest were compared at four sites on Sumba, Indonesia that differed in terms of protection and exhibited associated differences in levels of human disturbance. A numerical method employing principal components analysis was devised for describing forest structure at each site. The first principal component (PRINI) grouped attributes tending towards dense forest with closely-spaced trees, a closed canopy and a poorly developed field layer, with trees that tended to be large with the point of inversion in the upper half of the trunk. The highest values for PRINI were recorded within protected forest, and PRINI values were considered to be a useful index of forest disturbance at each site. Species diversity of butterflies was highest in unprotected secondary forest, but was not affected by lower levels of disturbance. Those species occurring at highest density in secondary forest generally had wide geographical distributions, whereas those species occurring at highest density in undisturbed primary forest had restricted ranges of distribution, in most cases with a separate subspecies on Sumba. Overall, an index of biogeographical distinctiveness decreased with increasing disturbance, and this supports the hypothesis that the most characteristic species of undisturbed climax forest have the smallest geographical ranges of distribution. Species abundance data for butterflies fitted a log-normal distribution at all but the most disturbed site. These results indicate that the pattern of proportional abundance of tropical butterfly species may be used as an 'instantaneous' indicator of forest disturbance, and that changes in the structure of tropical forests in S.E. Asia resulting from human disturbance, even within partially-protected forest, may result in the presence of butterfly assemblages of higher species diversity but of lower biogeographical distinctiveness, and therefore of lower value in terms of the conservation of global biodiversity.

L. A. Lace

Papers

Effects of selective logging on tropical forest butterflies on Buru, Indonesia

Ecological and biogeographical effects of forest disturbance on tropical butterflies of Sumba, Indonesia