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This study investigates the zone of overlap and hybridization between a new species in the Allonemobius species complex and Allonemobius socius (Scudder 1877). The new species, Allonemobius sp. nov. Tex was previously misidentified as Allonemobius fasciatus (De Geer 1773). Our survey of genetic variation at 13 allozyme loci shows that the new species differs from A. fasciatus in at least two allozyme loci. A. sp. nov. Tex is distributed mainly in Texas, and it is sympatric with A. socius in some parts of its distribution where the two species hybridize. In addition to the two fixed allelic differences between the two species, there is also a unique allele at a third locus in A. sp. nov. Tex. The proportion of hybrids in the mixed populations where the two species co-occur is always low, resulting in bimodal hybrid index scores. The bimodal distribution suggests that there is reproductive isolation between the new species and A. socius. This reproductive isolation is maintained, at least in part, through conspecific sperm precedence, which also serves as the major barrier to gene flow between A. socius and A. fasciatus.

Speciation continues to be one of the most intriguingphenomena in evolutionary biology; even though ourunderstanding of many of the mechanisms involved duringspeciation has improved considerably in the last twodecades (Howard and Berlocher 1998, Gavrilets 2004,Coyne and Orr 2004). Recently, Emerson and Kolm(2005) suggested a new agent that could potentially drivespeciation: species diversity itself. Emerson and Kolm(2005) argued that data on numbers of endemic speciesindicate that speciation rate increases with increasing plantand arthropod diversity on the Canary and HawaiianIslands. According to Emerson and Kolm, the proportionof endemic species in taxonomic groups can be used as asurrogate for speciation rate because that proportion isaffected mainly by in situ island speciation rather than byextinction and speciation on other islands (cf. Cadena et al.2005). It follows then that a higher proportion of endemicspecies means a higher in situ island speciation rate. Theproportion of endemic species was found to increase withincreasing diversity on the Canary and Hawaiian Islands,leading to the conclusion that species diversity itself couldbe driving speciation (Emerson and Kolm 2005).Emerson and Kolm’s (2005) study received skepticalresponses (Cadena et al. 2005, Kiflawi et al. 2007, Pereiraet al. 2007, Whittaker et al. 2007, Gruner et al. 2008) thatcame up with several reasons why Emerson and Kolm’s(2005) analysis fails to identify the agent responsible for theobserved relationship between the proportion of endemicsand species diversity. In one of these responses, Witt andMaliakal-Witt (2007) showed with a null model that therelationship can arise by chance alone through stochasticcolonizations and extinctions; however, their null model didnot incorporate speciation, extinction, and inter-islandcolonization. Our main interest is whether Witt andMaliakal-Witt’s (2007) conclusion still holds when theseprocesses are included.The null model presented here is constructed as apresence/absence matrix. The columns are islands and therows are species, where ‘‘1’’ means the species is presenton that island and ‘‘0’’ means absent. Species diversity onthese islands is determined by speciation, extinction, andmigration between the islands; each of which depends onchance. Each species has the same probability of undergoingthese events, and these probabilities are kept constantthroughout the simulation.Presence/absence matrices have been used widely forbuilding null models in community ecology and islandbiogeography (Connor and Simberloff 1979, 1983). Thesemodels have been very influential, but at the same time,have been criticized for potential statistical biases built intothe matrices (Diamond and Gilpin 1982, Wright and Biehl1982, Wilson 1995, Gotelli and Entsminger 2001, 2003).In these models, the ‘‘assemblies’’ of species on islands hasbeen the main interest, so the critical issue was the way ‘‘1’’sand ‘‘0’’s were distributed in a given matrix with fixedcolumn and/or row sums (Gotelli 2000). In our model,however, the distribution of ‘‘1’’s and ‘‘0’’s in the matrix isnot of interest. Moreover, in our model, the size of thematrix changes during the simulation; the matrix growswhen a new row is added after a speciation event (whichensures that the new daughter species is present only on thatisland and nowhere else) and shrinks if a species goes extincton all the islands. Migration between the islands does notaffect the matrix size, but converts the ‘‘0’’s to ‘‘1’’s if themigration event is successful. Thus, the model is unbiased asit does not test whether or not there are certain speciesassemblages on islands.At each time step, each species can potentially speciate,go extinct, or migrate to another island; whether they willdo so depends on chance determined by a random numberdrawn at each time step. For example, if the randomnumber drawn for a particular species is less than thespeciation probability assigned for that simulation, then thespecies undergoes a speciation event. After a speciationevent, the existing species on the island can potentially goextinct depending on the random number drawn at eachtime step for each species. As before, all the species have thesame extinction probability that remains constant through-out the simulation. Lastly, all species that survive on anisland can potentially migrate to other islands, thusreducing the proportion of endemics.

The exact nature of the relationship among species range sizes, speciation, and extinction events is not well understood. The factors that promote larger ranges, such as broad niche widths and high dispersal abilities, could increase the likelihood of encountering new habitats but also prevent local adaptation due to high gene flow. Similarly, low dispersal abilities or narrower niche widths could cause populations to be isolated, but such populations may lack advantageous mutations due to low population sizes. Here we present a large-scale, spatially explicit, individual-based model addressing the relationships between species ranges, speciation, and extinction. We followed the evolutionary dynamics of hundreds of thousands of diploid individuals for 200,000 generations. Individuals adapted to multiple resources and formed ecological species in a multidimensional trait space. These species varied in niche widths, and we observed the coexistence of generalists and specialists on a few resources. Our model shows that species ranges correlate with dispersal abilities but do not change with the strength of fitness trade-offs; however, high dispersal abilities and low resource utilization costs, which favored broad niche widths, have a strong negative effect on speciation rates. An unexpected result of our model is the strong effect of underlying resource distributions on speciation: in highly fragmented landscapes, speciation rates are reduced.

Distributional similarity (congruence) between phylogenetically independent taxonomic groups has important biogeographical as well as conservation implications. When multiple groups show congruence, one or two of them can be used as surrogates of diversity in others; thus, simplifying some of the challenges of area prioritization for conservation action. Here we test for congruence in complementarity between amphibians, reptiles and birds across seven tropical rainforest sites in the Eastern Himalaya and Indo-Burma global biodiversity hotspots. The results show that while frogs and lizards are strongly congruent with each other, birds as a whole do not show congruence with either of them. However, certain bird subgroups delineated on the basis of broad ecological niche and life history attributes are significantly congruent with both frogs and lizards. Multiple Mantel regression between environmental variable and species distribution dissimilarity matrices indicate that along with differential response to between-site ecological differences, inherent life-history characteristics shared by certain groups contributes to observed patterns of congruence. Our analyses indicate that examining biologically distinct subsets of larger groups can improve the resolution of congruence analyses. This approach can refine area-prioritization initiatives by revealing fine-scale discordances between otherwise concordant groups, and vice versa. Given that monetary resources do not always allow inclusion of multiple groups in biodiversity inventorying efforts, performing such analyses also makes economic sense because it can provide better resolution even with single-group data. In the context of conservation in North-east India, the results highlight the biogeographical complexity of the region, and also point at future priorities for biodiversity inventorying and conservation prioritization, both in terms of areas as well as taxonomic groups.