Vertebrates are poor umbrellas for invertebrates: cross-taxon congruence in an Australian tropical savanna

Abstract

Invertebrates are commonly ignored in conservation planning due to their vast diversity, difficulties with species identification, a poor understanding of their spatial patterns, and the impracticability of carrying out comprehensive sampling. Conservation planning for fauna is therefore often based on patterns of diversity and distribution of vertebrates, under the assumption that these are representative of animal diversity more generally. Here, we evaluate how well vertebrates act as umbrellas for invertebrate diversity and distribution in a highly diverse tropical savanna landscape, and we investigate the effect of vertebrate sampling intensity (i.e., number of surveys) on congruence results. We assessed congruence between each of the four classes of terrestrial vertebrates (amphibians, reptiles, birds, and mammals) and twelve invertebrate families (representing four dominant invertebrate taxa: ants, beetles, flies, and spiders) by applying a range of modeling approaches to analyze patterns of cross‐taxon congruence in species richness and composition across sampling sites. To investigate drivers of congruence, we applied generalized and distance‐based linear models to identify environmental associations of richness and composition for each taxon, then examined variation in environmental associations across taxa. Vertebrate and invertebrate richness was weakly (<30%) associated, and ~60% of the significant associations were negative. Correlations in species composition between vertebrate and invertebrate taxa were also weak, with a maximum of 13% congruence. In most cases, pairwise correlation scores using data from single surveys of vertebrates were only marginally lower than those from multiple surveys. Poor among‐site congruence between vertebrates and invertebrates was reflected by marked variation among taxa in their environmental associations. Our findings show that vertebrates are poor umbrellas for invertebrates in the tropical savannas of northern Australia in terms of geographic patterns of diversity and distribution and that this is not just an artifact of low vertebrate sampling intensity. Our study is one of the most comprehensive regional analyses of the congruence of vertebrate and invertebrate diversity, and it significantly adds to the growing evidence that empirical data on invertebrate diversity and distribution are required for conservation planning that effectively protects all faunal diversity.