Ann. Zool. Fennici 42: 463–475 ISSN 0003-455X Helsinki 29 August 2005 © Finnish Zoological and Botanical Publishing Board 2005 From communities to continents: beta diversity of herbivorous insects Vojtech Novotny1 & George D. Weiblen2 1) Institute of Entomology, Czech Academy of Sciences & Biological Faculty, University of South Bohemia, Branisovska 31, CZ-370 05 České Budějovice, Czech Republic (e-mail: novotny@entu. cas.cz) 2) Department of Plant Biology, University of Minnesota, 1445 Gortner Avenue, Saint Paul, Minnesota 55108, USA Received 22 Nov. 2004, revised version received 14 Mar. 2005, accepted 21 Mar. 2005 Novotny, V. & Weiblen, G. D. 2005: From communities to continents: beta diversity of herbivorous insects. — Ann. Zool. Fennici 42: 463–475. Recent progress in molecular systematics that assists species identifications, and in on-line databases of ecological and museum collections that enable the integration of insect distribution data represent important developments facilitating beta diversity studies. The increase in alpha and gamma diversities of insect herbivores from temper- ate to tropical communities is driven largely by a parallel increase in plant diversity while the diversity of insect herbivores per plant species remains constant. Likewise, the high beta diversity of insect herbivores along altitudinal gradients is only partially explained by changes in plant diversity, while abiotic factors and the abundance of natural enemies may also be important. The high alpha diversity of insect herbivores in lowland tropical forests is not matched by beta diversity as locally co-existing species represent a large proportion of regional species pools. The role of dispersal limitation in the distribution of herbivorous insects in tropical forests could be minor, as short- lived insects are efficient colonisers of their mostly long-lived woody hosts. Introduction city of beta-diversity studies. Ecologists have not consistently applied standardised survey proto- Beta diversity, or diversity among ecological cols to multiple sites and the study of changes in communities, is a Cinderella among biodiversity diversity among sites is impeded by incomplete parameters, overshadowed by her more popu- taxonomy for many insect groups. Despite these lar sisters, alpha and gamma diversities. While problems there are new data (Stork et al. 1997, alpha, the local diversity of a community, and Asher et al. 2001, Basset 2001, Benes et al. 2002, gamma, the regional diversity of species pools Basset et al. 2003) and theoretical developments from large geographic areas, are simply counts of (Hanski 1999, Hubbell 2001) that improve our species from a particular territory, beta diversity understanding of insect distribution. The present is a more abstruse concept measuring change in review uses this information to examine the species composition between communities. The factors that prevent species from being distrib- difficulty of surveying species from more than uted everywhere, and tries to identify promising one area is undoubtedly responsible for the scar- approaches to future beta diversity studies. 464 Novotny & Weiblen • ANN. ZOOL. FENNICI Vol. 42 Defining and measuring beta of species. As recently argued by Loreau (2000), diversity Gering and Crist (2002) and Veech et al. (2002), the additive partitioning of gamma diversity g = a b Alpha diversity characterises species richness avg + is more practical as all three parameters, in communities, assemblages of species poten- including beta diversity, can be measured in the tially involved in ecological interactions such as same unit, the number of species. competition or predation, while the term gamma The change in species composition from diversity is usually applied to species pools at community A to community B is fully described large spatial scales, formed primarily by specia- by three parameters: the number of species lost tion and dispersal (Ricklefs 1987). Spatial reso- (present in A but not B), species gained (present lution is necessarily defined rather vaguely and in B but not A), and species shared (present in may vary among species. Some authors use the A and B). Nested communities where A is a terms alpha and gamma diversities even more subset of B represent a special case with no spe- loosely to distinguish between point (alpha) cies loss. There are at least 24 measures of beta diversity and the gamma diversity of any larger diversity based on these parameters (Koleff et al. area, often obtained from a collection of mul- 2003a) including those sensitive only to compo- tiple point estimates. For instance, Gering and sitional differences between communities and Crist (2002) contrasted point and population those sensitive also to their differences in alpha samples of insects from a single tree, multiple diversity. trees at a single site, and multiple sites within a The differences in species composition larger area. Koleff and Gaston (2002) and Arita between two communities can also be quanti- and Rodriguez (2002) explored the effect of fied using similarity measures sensitive to spe- spatial resolution on beta-diversity estimates. cies abundance (Colwell & Coddington 1994). At low resolution, high beta diversity can reflect Condit et al. (2002) used the probability P(r) that local environmental heterogeneity. As sampling two randomly selected individuals separated by grain increases, biotic assemblages appear more distance r were conspecific. An important appli- homogeneous as each of the study areas encom- cation of this approach in beta diversity studies passes a wider range of the available environ- is to examine the decay of conspecific probabil- ments (Mac Nally et al. 2004). Alpha, beta and ity with increasing geographic distance between gamma terminologies and analytical approaches communities (Condit et al. 2002, Ricklefs 2004). have further served the study of changes in Chao et al. (2005) proposed estimators for the diversity among microhabitats within commu- classical Jaccard and Sørensen similarity indices nities and through time (de Vries et al. 1997). based on species abundance data that include the Vellend (2001) noted a distinction between the effect of shared species missed by the sampling. concept of beta diversity as among-plot vari- The probability that two individuals drawn ability in species composition independent of the from different communities are conspecific can position of individual plots on spatial or environ- be standardised by the analogous probability for mental gradients, and the concept of turnover in two individuals drawn from the same commu- species composition along predefined gradients. nity. This is the principle of Morisita’s index, a The former can be measured by the partitioning special case of the normalized expected species of regional diversity, the latter using matrices of shared index, NESS(m) (Grassle & Smith 1976). compositional similarity and physical or envi- NESS(m) estimates the number of common spe- ronmental distances among pairs of study plots. cies for random draws of a particular number of Regional gamma diversity can be partitioned individuals m from two different communities a into the average local alpha diversity ( avg) and and compares this estimate with the number of between-site beta diversity ( b) in either a mul- common species resulting from random draws tiplicative or additive fashion. Whittaker (1972) from the same community. It ranges from 0 b g a originally defined beta diversity as = / avg, a (no common species) to 1 (samples are random dimensionless number that relates gamma diver- samples from the same community). NESS(m) sity to alpha diversity, each measured in numbers is a more general case of Simpson’s index. The ANN. ZOOL. FENNICI Vol. 42 • From communities to continents: beta diversity of herbivorous insects 465 sum of the squared proportional abundances is the probability that two individuals drawn at random belong to the same species. The com- temperate E F plement of Simpson’s index, also known as bEF bCE b the Gini coefficient, is the probability that two DF individuals drawn at random belong to differ- C D Latitude b ent species. Robinson and Tuck (1993), Frenzel CD bAC b and Brandl (2001) and Walla et al. (2004) used BD similar approaches relating observed differences A B b between two communities to probabilistic esti- AB mates of the expected number of shared species tropical between two samples drawn from the same com- lowland montane munity. Altitude The complete census of species in many insect communities is very difficult to achieve Fig. 1. Two approaches to measuring beta diversity with due to numerous rare species (Novotny & Basset respect to environmental gradients: (i) The analysis of 2000) that can be discovered only in very large latitudinal gradients in community composition relates the change in latitude, from tropical to temperate, to the samples (Longino et al. 2002). Relying on change in the species composition of insect communi- NESS(m) or other probabilistic measures avoids ties, measured as beta diversity bAC, bCE in the lowlands the often serious overestimation of beta diver- and bBD, bDF in the mountains; (ii) The analysis of a lati- sity based on simple comparisons of incomplete tudinal gradient in beta diversity relates the change in species lists. Although NESS(m) is more robust latitude to the change in beta diversity between insect communities from the same latitude (bAB, bCD, bEF). The to biases in sample size than some measures of present example illustrates