Biotic communities of freshwater marshes and mangroves in relation to saltwater incursions: implications for wetland regulation

An ecosystem-level study was conducted in the Guandu wetlands in subtropical coastal Taiwan to examine how salinity influences the abundance, diversity, and structure of biotic communities. We surveyed eight permanent study sites, spanning freshwater marshes, to the gate on the dyke, and mesohaline mangroves representing a gradient of the extent of saltwater incursions. Analyses of abiotic variables showed that salinity was the primary determining factor for discriminating habitat types in the wetlands, but communities differed in their sensitivity to salinity. The composition of plant and insect communities was most affected by the salinity gradient, suggesting the utility of these communities for ecological monitoring of saltwater incursions. However, spatial changes in communities at higher trophic levels, including macrobenthos, mollusks, fish, and birds, could not be explained simply by the salinity gradient. Instead, changes in these communities were more relevant to the composition of other biotic communities. Our results show that species richness and diversity of plant communities were higher in the marshes than in the mangroves. Nevertheless, insect communities censused in the mangroves had higher diversity, despite lower abundance and species richness. Macrobenthos surveyed in the mangroves showed higher biomass and number of taxa. Mollusks and fish were also more abundant at sites near the gate compared to the marsh sites. This suggests that maintaining a tidal flux by means of gate regulation is necessary for conserving the spatial heterogeneity and biodiversity of coastal wetlands

Out of Gondwanaland; the evolutionary history of cooperative breeding and social behaviour among crows, magpies, jays and allies

Cooperative breeding is comparatively rare among birds in the mainly temperate and boreal Northern Hemisphere. Here we test if the distribution of breeding systems reflects a response to latitude by means of a phylogenetic analysis using correlates with geographical range among the corvids (crows, jays, magpies and allied groups). The corvids trace their ancestry to the predominantly cooperative ‘Corvida’ branch of oscine passerines from the Australo-Papuan region on the ancient Gondwanaland supercontinent, but we could not confirm the ancestral state of the breeding system within the family, while family cohesion may be ancestral. Initial diversification among pair-breeding taxa that are basal in the corvid phylogeny, represented by genera such as Pyrrhocorax and Dendrocitta, indicates that the corvid family in its current form could have evolved from pair-breeding ancestors only after they had escaped the Australo-Papuan shield. Within the family, cooperative breeding (alloparental care/family cohesion) is strongly correlated to latitude and its predominance in species maintaining a southerly distribution indicates a secondary evolution of cooperative breeding in the lineage leading away from the basal corvids. Multiple transitions show plasticity in the breeding system, indicating a response to latitude rather than evolutionary inertia. The evolutionary background to the loss of cooperative breeding among species with a northerly distribution is complex and differs between species, indicating a response to a variety of selection forces. Family cohesion where the offspring provide alloparental care is a main route to cooperatively breeding groups among corvids. Some corvid species lost only alloparental care, while maintaining coherent family groups. Other species lost family cohesion and, as a corollary, they also lost the behaviour where retained offspring provide alloparental care