Cross-taxon surrogacy of biodiversity in the Indian Garhwal Himalaya

Abstract

Biodiversity surveys were conducted in 13, 10×50 m² plots located between 1400 to 3700 m above mean sea level in a range of habitats in temperate mixed Oak and Coniferous forests through sub-alpine to the alpine grasslands in Chamoli district of Uttaranchal state in the Indian Garhwal Himalaya. Cross-taxon congruence in biodiversity (α-diversity and β-diversity) across macrolichens, mosses, liverworts, woody plants (shrubs and trees) and ants was investigated, so as to examine the extent to which these groups of organisms can function as surrogates for each other. Although woody plants provided a major substrate for macrolichens and mosses, there was no species-specific association between them. Woody plant species richness was highly positively correlated with mosses (r²=0.63, P<0.001), but the relationship was not particularly very strong with lichens and liverworts. While there was a significant correlation in the species turnover (β-diversity) of macrolichens with mosses (r²=0.21, P<0.005), the relationship was relatively poor with the woody plants. On the other hand, negative correlations emerged in the species richness of ants with those of macrolichens, mosses and woody plants (r²=−0.44, P<0.05), but most of the complementarity (turnover) relationships among them were positive. Since diversity between taxonomic hierarchies within the group was consistently significantly positively correlated in all these taxa, the higher taxonomic categories such as genus and family may be employed as surrogates for rapid assessment and monitoring of species diversity. Although no single group other than macrolichens has emerged as a good indicator of changes in species richness in all other groups, some concordant relationships between them conform to the hypothesis that species assemblages of certain taxonomic groups could still be used as surrogates for efficient monitoring of species diversity in other groups whose distribution may further predict the importance of conserving overall biodiversity in landscapes such as the Garhwal Himalaya.

Introduction

Exploring distribution of biological diversity and the extent of surrogacy among different sets of organisms are importantly challenging scientific problems in conservation biology (UNEP, 1992, Heywood, 1995, Faith & Walker, 1996, Gaston, 1996, Gaston, 2000, Negi, 1999). The problem has been particularly investigated in the context of designing efficient programs of monitoring biodiversity and setting out conservation priorities (Pollard & Yates, 1993, Oliver & Beattie, 1993, Balmford & Long, 1995, Gadgil, 1996, Howard et al., 1998, Swengel & Swengel, 1999, Myers et al., 2000). In these contexts, there is a need to assess the extent to which high levels of diversity are correlated among different taxonomic groups in different bio-geographical regions. The organismic groups may be distinctive taxa such as ants and flowering plants, or nested taxonomic groups such as liverworts, mosses and bryophytes. By and large, no consistent levels of positive correlations have been found among distinct taxa, at levels of different types of habitats, such as forests with different levels of human disturbance, or large geographical regions, such as different grids into which the British Isles are divided (Prendergast et al., 1993, Lawton et al., 1998, Kunte et al., 1999, Pharo et al., 1999). As may be expected, higher, though variable, levels of correlations have been recorded among groups within a nested taxonomic hierarchy at different spatial scales (Noss, 1990, Williams & Gaston, 1994, Andersen, 1995). This is because organisms within such a hierarchy have similar responses to a variety of environmental parameters. In fact, one may postulate that the extent of correlation in levels of diversity in different habitats or geographical locales among different taxa would depend upon similarities or differences in their responses to biotic as well as abiotic parameters and mutualistic, competitive, or antagonistic (prey–predator, host–parasite) relationships amongst the different taxa. In the present study, an attempt is made to explore the possible influence of such factors by looking at five distinctive groups of organisms with variable levels of differences in their responses to environmental parameters and types of biotic interactions. The groups under investigation include macrolichens, mosses, liverworts, woody plants and ants. The lichens and bryophytes accounting for the first three groups occur on soil, rock and wood substrates. Shrubs and trees primarily growing on soil serve as wood substrate for macrolichens and mosses. The ants prefer drier soils underneath rocks, logs and thick moss beds for nesting whereas terricolous liverworts exclusively prefer wet soil. Owing to these habitat preferences, patterns of diversity of macrolichens, mosses and woody plants may be expected to be positively correlated, but be uncorrelated, or perhaps even be negatively correlated with those of liverworts and ants. Another hypothesis of interest may be postulated as while macrolichens and mosses extensively use live woody substrates, they may not be species specific. So while the species richness (α-diversity) of macrolichens and mosses may be positively correlated with that of woody plants, their levels of species turnover (β-diversity) may show little correlation. This investigation further addresses the environmental variables including the local land use factors that may explain significant variation in species richness and turnover in one group of organisms also explaining the variations in other surrogate groups. For example, livestock grazing, excessive lopping and fuel wood collection, especially for sustaining growing tourism in the area urgently needs to be regulated with high priority. If we do not control and monitor such land use patterns and their biodiversity implications, future generation will have to face with local extinction of many species, including wood loving macrolichens and mosses, some of which are medicinal and critical for the survival of the highly endangered Musk deer in the higher Himalaya (Negi, 1996, Negi, 1999, Negi, 2000a, Negi & Gadgil, 1996).