Taxonomic distinctness along nutrient gradients: More diverse,less diverse or not different from random?

Taxonomic distinctness indices are a family of anthropogenic stress indicators that have been used widely in marine ecosystems; however, their utility in freshwater ecosystems is still unclear. We used two taxonomic distinctness indices and species richness to assess relationships between nutrient gradients and three freshwater taxonomic groups, including diatoms, macrophytes and invertebrates. We found that the indices based on the three organismal groups showed generally rather clear relationships with the nutrient levels, indicating that these indices may bring useful additional information for the purposes of bioassessment. However, the two indices describing taxonomic distinctness showed opposite patterns in relation to nutrient levels. The indices for the three groups of organisms were generally poorly correlated with each other, showing that different organismal groups react differently to anthropogenic stress. Accordingly, taxonomic distinctness indices likely tell us about various aspects of nutrient enrichment of freshwater ecosystems. Our findings also emphasized that the value of these indices may be largely dependent on the organismal group used.     

The mid-domain effect and diversity gradients: is there anything to learn?

The mid-domain effect (MDE) has been proposed as a null model for diversity gradients and an explanation for observed patterns. Here we respond to a recent defense of the concept, explaining that it cannot represent a viable model in either real or null worlds. First, the MDE misrepresents the nature of species ranges. There is also an internal logical inconsistency underlying the MDE because the range size frequency distribution, necessary to generate a hump-shaped pattern under randomization, cannot exist in the absence of environmental gradients and is generated by the ecological and historical processes that the MDE claims to exclude.     

Ecological impacts of tropical forest fragmentation: how consistent are patterns in species richness and nestedness?

Large areas of tropical forest now exist as remnants scattered across agricultural landscapes, and so understanding the impacts of forest fragmentation is important for biodiversity conservation. We examined species richness and nestedness among tropical forest remnants in birds (meta-analysis of published studies) and insects (field data for fruit-feeding Lepidoptera (butterflies and moths) and ants). Species-area relationships were evident in all four taxa, and avian and insect assemblages in remnants typically were nested subsets of those in larger areas. Avian carnivores and nectarivores and predatory ants were more nested than other guilds, implying that the sequential loss of species was more predictable in these groups, and that fragmentation alters the trophic organization of communities. For butterflies, the ordering of fragments to achieve maximum nestedness was by fragment area, suggesting that differences among fragments were driven mainly by extinction. In contrast for moths, maximum nestedness was achieved by ordering species by wing length; species with longer wings (implying better dispersal) were more likely to occur at all sites, including low diversity sites, suggesting that differences among fragments were driven more strongly by colonization. Although all four taxa exhibited high levels of nestedness, patterns of species turnover were also idiosyncratic, and thus even species-poor sites contributed to landscape-scale biodiversity, particularly for insects.     

Latitudinal gradients in butterfly body sizes: is there a general pattern?

We tested for the existence of latitudinal gradients in the body sizes of butterflies in North America, Europe, Australia and the Afrotropics. We initially compared body sizes (measured as male forewing length) of all butterflies found in 5° latitudinal bands in each region, and then evaluated the relationship between body size and latitude statistically using the latitudinal midpoint of each species' distribution. Trends were examined for species in all butterfly families together and for each family separately. We found that gradients in body sizes were inconsistent in different geographical regions and butterfly families; in some cases species were larger towards the tropics, in some they were smaller, and in other cases there were no relationships. Most of the gradients, when they existed, reflected between-family effects arising from changes in the relative numbers of species in each family across regions. We conclude that general ecological explanations for geographical trends in butterfly body sizes are inappropriate, and gradients largely reflect historical patterns of speciation within and between taxa in each biogeographical realm. Thus, the robustness of body size gradients found in other insect groups should be confirmed in future studies by including more than one geographical region whenever possible.     

Investigating causality of nestedness of insular communities: selective immigrations or extinctions?

Abstract. Most archipelagos are comprised of a nested set of communities, with species on depauperate islands representing proper subsets of those on richer islands. The causality for this common intra-archipelago pattern, however, remains elusive. Here, I present a Monte Carlo approach for investigating whether nestedness results from selective extinctions, selective immigrations, or both. Results for mammal communities of three nearshore archipelagos and two montane forest archipelagos suggested that nestedness may result from both forces. Nestedness was significantly associated with area (extinctions) for all archipelagos studied, and with isolation (immigrations) for islands of Lake Huron and the American Southwest. The degree of nestedness is influenced by the degree of variations among species and islands. In addition, our ability to assess causality of nestedness is influenced by our ability to calculate biologically relevant measures of isolation, and by the potentially confounding effects of selective immigrations and extinctions on community nestedness.     

Superorganisms or loose collections of species? A unifying theory of community patterns along environmental gradients

The question whether communities should be viewed as superorganisms or loose collections of individual species has been the subject of a long‐standing debate in ecology. Each view implies different spatiotemporal community patterns. Along spatial environmental gradients, the organismic view predicts that species turnover is discontinuous, with sharp boundaries between communities, while the individualistic view predicts gradual changes in species composition. Using a spatially explicit multispecies competition model, we show that organismic and individualistic forms of community organisation are two limiting cases along a continuum of outcomes. A high variance of competition strength leads to the emergence of organism‐like communities due to the presence of alternative stable states, while weak and uniform interactions induce gradual changes in species composition. Dispersal can play a confounding role in these patterns. Our work highlights the critical importance of considering species interactions to understand and predict the responses of species and communities to environmental changes.     

Fertility and mortality patterns of captive Bornean and Sumatran orangutans: is there a species difference in life history?

Across broad taxonomic groups, life history models predict that increased ecological predictability will lead to conservative investment in reproductive effort. Within species, however, organisms are predicted to have increased reproductive rates under improved environmental conditions. It is not clear how these models apply to closely-related species. In this paper, we examine predictions from these models as applied to variability in reproductive rates between the two species of orangutans, Pongo pygmaeus (Bornean) and Pongo abelii (Sumatran). Orangutans exhibit characteristics of a "slow" life history strategy with large bodies, late age at maturity, low reproductive rates, and long lifespan. Recently, researchers proposed that Sumatran orangutans may have an even slower life history than Bornean orangutans as a result of ecological and genetic differences (Wich et al., 2004). We examined this hypothesis by studying important aspects of life history of both species under conditions of relative ecological stability, in captivity. In this large dataset, there were no significant species differences in age of first or last reproduction, completed fertility, perinatal and postnatal mortality, or female longevity. Bornean orangutans in captivity did have significantly longer interbirth intervals, and male Bornean orangutans had higher survival past maturity. Our results do not support the hypothesis that selection has led to decreased reproductive effort under conditions of increased habitat quality in Sumatra (Wich et al., 2004), and instead suggest that phenotypic flexibility may be particularly important in explaining differences between closely related species.     

Spatial structure and β-diversity of phytoplankton in Tibetan Plateau lakes: nestedness or replacement?

Hydrobiologia - Spatial patterns and β-diversity of phytoplankton assemblages depend on the relative importance of species dispersal capacity and species-sorting. Variability in species...     

Primary cilia and organogenesis: is Hedgehog the only sculptor?

The primary cilium is a small microtubule-based organelle projecting from the plasma membrane of practically all cells in the mammalian body. In the past 8 years, a flurry of papers has indicated a crucial role of this long-neglected organelle in the development of a wide variety of organs, including derivatives of all three germ layers. A common theme of these studies is the critical dependency of signal transduction of the Hedgehog pathway upon functionally intact cilia to regulate organogenesis. Another common theme is the role that the cilium plays, not necessarily in the determination of the embryonic anlagen of these organs, although this too occurs but rather in the proliferation and morphogenesis of the previously determined organ. We outline the various organ systems that are dependent upon primary cilia for their proper development and we discuss the cilia-dependent roles that Sonic and Indian Hedgehog play in these processes. In addition and most importantly for the field, we discuss the controversial involvement of another major developmental pathway, Wnt signaling, in cilia-dependent organogenesis.     

Blood feeding patterns of mosquitoes: random or structured?

Background

During the non-breeding period, many birds migrate to milder areas, found closer to the equator than their breeding sites. Opposite movements are very rare. In the Southern Ocean, the abundance of ¹³C declines markedly with more southern latitude, providing a characteristic ¹³C isoscape. This can be used as a tracer for the movement of seabirds between breeding and inter-breeding areas, by comparing stable isotope ratios of feathers grown at different times of the year.

Results

We studied seasonal movements of Thin-billed prions (Aves, Procellariiformes), breeding at the Subantarctic Falkland/Malvinas Islands, compared with those of Wilson's storm-petrels breeding in the Antarctic South Shetland Islands. The two species showed opposite migratory movements. While Wilson's storm-petrels moved to warmer waters north of the Drake Passage in winter, Thin-billed prions showed a reversed movement towards more polar waters. Carbon stable isotope ratios in recent and historical feathers indicated that poleward winter movements of Thin-billed prions were less common historically (45% in 1913-1915), and have only recently become dominant (92% in 2003-2005), apparently in response to warming sea temperatures.

Conclusions

This study shows that pelagic seabirds can rapidly change migration strategies within populations, including migration towards more poleward waters in winter.     

Obesity and the rate of time preference: is there a connection?

It is hypothesized that recent trends in US and worldwide obesity are, in part, related to an increase in the marginal rate of time preference, where time preference refers to the rate at which people are willing to trade current benefit for future benefit. The higher the rate of time preference, the larger is the factor by which individuals discount the future health risks associated with current consumption. Data from the United States, as well as international evidence, suggest that a relationship between these two variables is plausible. The authors encourage researchers to explore the possible link between obesity and time preference, as important insights are likely to result.