Desert goby (Chlamydogobius eremius) behaviours in arid Australian waterholes: community level interactions and individual level variability

How aquatic organisms survive in the vast arid landscapes of central Australia is an ecological question which can provide critical insights into the factors underpinning persistence of biodiverse communities. Some community theory has suggested that species-rich and complex food-webs are inherently unstable, but recent modelling has shown that factors such as adaptive foraging and within-species trophic variability may compensate for this instability and facilitate species persistence and coexistence. The potential role of temperament (i.e., consistent within-species differences in behaviour) in population and community stability is an intriguing knowledge gap, particularly as recent empirical analysis suggests that temperament is related to food-web interactions (Chapter 1). Using the striking natural physical contrasts between waterbodies in arid Australia, I analysed the food-web characteristics of aquatic communities and the individual-level trophic variability of the widely dispersed Australian desert goby(Chlamydogobius eremius). I analysed goby temperament and patterns of behavioural divergence in the context of gobies’ trophic niche. Employing and integrating community and behavioural ecology perspectives, this thesis sought to explore how the desert goby survives in a challenging desert environment. Stable isotope and community composition analysis was used to investigate community responses to environmental pressures. I compared aquatic communities from stable, isolated Great Artesian Basin springs and hydrologically variable river waterholes in the largely ephemeral Lake Eyre Basin (Chapter 2). I found that although species composition varied between habitats, community structure variables were remarkably consistent, including trophic length, community niche size and species-richness. The isotopic niche size of specific functional groups did differ between habitats. Similarly, in the desert goby, variability in individual isotope signatures indicated within-population resource segregation and intraspecific trophic variability between habitats(Chapter 3). In spring populations, the level of intraspecific trophic variability was positively correlated with community niche size, suggesting this is limited by prey diversity. By contrast, trophic variability in river populations was associated the physio-chemical environment, where disturbance-prone ephemeral sites showed extremely low intraspecific variability, suggesting populations tend to increase between-individual trophic variability over time. These results highlight the importance of functional group and population-level effects to dynamics of food-webs. Spring and river populations are subject to contrasting ecological pressures, and divergence in goby temperament traits was a key adaptive response. Behavioural assays focusing on risk-taking and dispersal traits were conducted on wild populations (Chapter 4) and first generation fish raised in a common garden environment (Chapter 5). This revealed inherent divergence in goby temperament. Specifically, spring fish were less active and bolder, which is likely to be associated with lower predation pressure and increased intraspecific competition in springs. Furthermore, correlations between traits differed within spring and river fish, where only river fish appeared to show an adaptive behavioural syndrome related to exploration and dispersal. These results reveal the importance of individual-level behavioural traits to animals persisting under complex ecological stressors, and the value of studying behaviour within a community context. Similarly, the patterns of individual behavioural and trophic variability underscore their potential significance to food-web structure and dynamics.