Jf Stuart-Smith

Integrating abundance and functional traits reveals new global hotspots of fish diversity

Species richness has dominated our view of global biodiversity patterns for centuries. The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management. However, this is changing rapidly, as it is now recognized that not only the number of species but the species present, their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions (such as biomass production and nutrient cycling). Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts. Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits. We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites, spanning 133 degrees of latitude from all ocean basins, to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean. These relate to high diversity of functional traits amongst individuals in the community (calculated using Rao’s Q), and differ from previously reported patterns in functional diversity and richness for terrestrial animals, which emphasize species-rich tropical regions only. There is a global trend for greater evenness in the number of individuals of each species, across the reef fish species observed at sites (‘community evenness’), at higher latitudes. This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness. Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales, and imply that in tropical regions, which have higher numbers of species, each species contributes proportionally less to community-level ecological processes on average than species in temperate regions. Metrics of ecological function usefully complement metrics of species diversity in conservation management, including when identifying planning priorities and when tracking changes to biodiversity values.

The role of body size in competition and mate choice in an agamid with female-biased size dimorphism

Competition and mate choice are fundamentally important components of social systems. We investigated intra-sexual competition and inter-sexual competition (mate choice) in Rankinia diemensis, an agamid lizard with female-biased size dimorphism. We examined intra-sexual interactions during contests and mate choice in relation to body size for both males and females. In male-male competition trials, proportions of two display types differed depending on body size, with more tail flicks produced by bigger males, and more hand-waves displayed by smaller males. These behaviours hold particular biological significance for agamid lizards; tail-flicks convey aggressiveness and, therefore, dominance, while hand-waves often denote submissiveness. In female-female competition trials, a greater difference in body size between the two conspecifics resulted in the larger female directing more pushes towards the smaller female. This female competition may be important in the social system and could be involved in resource defence. We found no indication of size-based mate choice for males or females. This suggests mate preferences may not be based on body size in this species. This may be linked to female-biased size dimorphism in this species, but it also supports previous studies that have failed to demonstrate female choice in reptiles.

Loss of native rocky reef biodiversity in Australian metropolitan embayments.

Urbanisation of the coastal zone represents a key threat to marine biodiversity, including rocky reef communities which often possess disproportionate ecological, recreational and commercial importance. The nature and magnitude of local urban impacts on reef biodiversity near three Australian capital cities were quantified using visual census methods. The most impacted reefs in urbanised embayments were consistently characterised by smaller, faster growing species, reduced fish biomass and richness, and reduced mobile invertebrate abundance and richness. Reef faunal distribution varied significantly with heavy metals, local population density, and proximity to city ports, while native fish and invertebrate communities were most depauperate in locations where invasive species were abundant. Our study adds impetus for improved urban planning and pollution management practises, while also highlighting the potential for skilled volunteers to improve the tracking of changes in marine biodiversity values and the effectiveness of management intervention.

The effects of turbidity and complex habitats on the feeding of a galaxiid fish are clear and simple

The habitat used by animals plays an important role in their interactions with predators and prey. By using complex habitats such as areas of dense macrophyte cover in response to elevated predation risk, small fishes may reduce their foraging success. Because the threat of predation by introduced brown trout increases the use of complex habitats by the threatened Galaxias auratus (Johnston), we experimentally examined its foraging in different habitats to estimate indirect impacts of brown trout presence. The lakes in which G. auratus lives have recently become more turbid, so the experiment was also conducted under different turbidity levels. Laboratory feeding trials in which planktonic and epibenthic prey were simultaneously offered to G. auratus in the presence or absence of artificial macrophytes and at three turbidity levels (0, 50 and 100 NTU) revealed that its overall foraging success was unaffected by habitat complexity; however, in trials with artificial macrophytes, G. auratus consumed a greater proportion of planktonic prey than in the absence of artificial macrophytes. Neither overall foraging success nor prey selection by G. auratus was affected by high turbidity, indicating that water clarity does not appear to directly negatively impact its feeding. The switch in prey types would probably not be detrimental to G. auratus in the long term, and thus it appears that there is no substantial feeding cost associated with its increased use of complex habitats. It could, however, affect lower trophic levels in the lakes to which it is endemic.

Southernmost records of two Seriola species in an Australian ocean-warming hotspot

Changes in marine species distributions in response to climate warming are being observed globally. However, there is great variation in the magnitude and rate of species responses. South-eastern Australia represents a global hotspot for ocean warming and, subsequently, numerous poleward extensions in marine species distributions are evident within the region. We report on two species of Carangid not previously found in this region, recorded through photo-verified observations by citizen scientists. This includes the first record of Amberjack (Seriola dumerili) in eastern Tasmania and an extension of the previously most southern reported observation of a similarly mobile congener, the Yellowtail kingfish (Seriola lalandi) along south-eastern Tasmania. Out-of-range observations may simply represent vagrant individuals; however, there is also evidence that they are often indicators of future colonisation potential. Moreover, the observations presented here are potentially representative of a range of climate-driven changes to marine biodiversity in this region and highlight the utility of community observations in acting as an effective early-warning system for reporting changes in the marine environment. Early detection and reporting of distributional changes are important for proactive environmental management, and is enhanced by establishing an informed community and mechanisms for conveying these observations to science and management authorities.