No abstract

We explored how range expansion of freshwater fishes coincident with climate warming is affected by, and then in turn affects, responses to a second environmental gradient; dissolved oxygen. Traits related to hypoxia tolerance, specifically various metrics of gill size and geometric morphometric proxies of gill size were quantified for a range-expanding cyprinid fish (Enteromius apleurogramma) in both its historical and novel ranges in the Mpanga River drainage of Uganda, East Africa. We found that E. apleurogramma followed patterns previously established in the congener E. neumayeri. Gill filament length and some other metrics were strongly divergent in long-established populations of both E. apleurogramma and E. neumayeri, with larger gills in hypoxic populations compared to normoxic ones. Range-expanding populations were intermediate to the two long-established populations, but divergent between themselves. Other gill traits such as filament number were weakly or not divergent. Furthermore, we show that grosser morphological traits such as opercular area can be successfully used as a proxy for gill size, both by direct measurement as well as using geometric morphometric techniques. Finally, we show that both parapatric conspecific populations and sympatric heterospecific populations can be used as reference points to approximate the ‘target’ of adaptation to hypoxic conditions.

An insular environment or "island" is any area of habitat suitable for a specific ecosystem that is surrounded by an expanse of unsuitable habitat.Examples of insular systems include mountain tops, lakes, seamounts, enclosed seas, and isolated islands or reefs. These systems have several important properties that set them apart from non-insular systems and thus dictate their specific consideration in this assessment. … Many of these problems facing insular taxa are compounded when the insular habitats are very small and isolated, including tiny remote Pacific islands, alpine lakes, and desert oases. … Finally, the small population sizes typical of species living in small insular habitats can lead to genetic drift and inbreeding that greatly reduce genetic variation in some situations. As insular taxa are often very local, rare,

Marine snails of the genus Littorina are found on rocky intertidal shores throughout the north Atlantic and north Pacific oceans and comprise 19 species (Reid, 1996). This genus is commonly used for population genetic studies; Littorina species typically have separate sexes, moderately short generation times, low adult dispersal rates and large intertidal populations, making them convenient for comparative genetic studies (Berger, 1973;

Foundation species traits that structure communities are rarely experimentally examined; thus, a predictive understanding of their functions lags behind patterns of observed species associations. Red mangrove Rhizophora mangle roots form complex living habitats that support diverse epibiont communities, making them a model system for testing links between variation in foundation species traits and associated biodiversity. Here, we compared epibiont community composition between living and non-living mangrove roots, as well as root mimics, to test how foundation species traits affect community structure. We also quantified the community structure of associated mobile invertebrates to examine their relationship with secondary foundation species (e.g. sponges, bivalves) that grow on the roots. After 14 mo of colonization and succession, substrate composition (i.e. mangrove, wood, PVC) had significant effects on community composition, richness, and abundance of sessile epibionts and mobile invertebrates. Non-living mangrove roots were 5 times more likely to deteriorate, and consequently had the lowest epibiont richness and abundance. We found strong positive relationships between mobile invertebrate richness and the abundance, measured as biomass, and richness of sponges and bivalves, suggesting that variation among roots in secondary foundation species play an important role in mediating mobile invertebrate community composition. This study highlights the functional role of habitat structure and how rapidly that function can be lost without biogenic maintenance. Our results indicate the importance of facilitation cascades in fostering diverse mobile invertebrate communities and highlight both advantages and limitations in using artificial structures in restoration programs.