Amy E. Deacon

Predation pressure shapes brain anatomy in the wild

There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies (Poecilia reticulata) from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator’s biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.

Association tendency and preference for heterospecifics in an invasive species.

Animals gain benefits by forming groups with phenotypically and behaviourally similar individuals. The most common groups are homogenous, composed by conspecifics, although in some cases associations of similar organisms of different species have been reported when individuals benefit from it. In this study, we tested the prediction that the Trinidadian guppy, Poecilia reticulata, a fish that has successfully invaded at least 70 countries, will shoal with heterospecifics. We measured shoaling tendency and shoal companion preference in wild-caught female guppies when they encounter two heterospecific species: the native Poecilia picta and the non-native Poecilia sphenops, a poeciliid recently introduced in Trinidad. Our results show that guppies have a higher tendency to shoal with conspecifics; if the alternative is be alone, they readily shoal with both species even when they have had no previous experience with other poeciliids. Individuals in these associations could benefit from safety in numbers along with other advantages of group living. This predisposition to associate with other species that share similar ecological conditions could explain the guppy’s success as invasive species as it enables them to increase their shoal size during the first stages of invasion and thus avoid Allee effects.

Divergent biodiversity change within ecosystems

Significance The world’s biodiversity is under unprecedented threat due to human activities, yet we have an incomplete understanding of ecosystem change in response to these pressures. Here we present data from a new 5-y study of a tropical freshwater ecosystem showing that change in the two dimensions of biodiversity—assemblage diversity (number and abundance of species) and assemblage composition—is decoupled from and uncorrelated among taxa. Assemblage diversity is typically stable over time. However, in line with Darwin’s expectation that community composition is constantly changing, this stability can be accompanied by marked turnover in species identities. Our paper thus identifies an important question for future research: at what point does compositional turnover threaten ecosystem resilience? The Earth’s ecosystems are under unprecedented pressure, yet the nature of contemporary biodiversity change is not well understood. Growing evidence that community size is regulated highlights the need for improved understanding of community dynamics. As stability in community size could be underpinned by marked temporal turnover, a key question is the extent to which changes in both biodiversity dimensions (temporal α- and temporal β-diversity) covary within and among the assemblages that comprise natural communities. Here, we draw on a multiassemblage dataset (encompassing vertebrates, invertebrates, and unicellular plants) from a tropical freshwater ecosystem and employ a cyclic shift randomization to assess whether any directional change in temporal α-diversity and temporal β-diversity exceeds baseline levels. In the majority of cases, α-diversity remains stable over the 5-y time frame of our analysis, with little evidence for systematic change at the community level. In contrast, temporal β-diversity changes are more prevalent, and the two diversity dimensions are decoupled at both the within- and among-assemblage level. Consequently, a pressing research challenge is to establish how turnover supports regulation and when elevated temporal β-diversity jeopardizes community integrity.

Evaluating detectability of freshwater fish assemblages in tropical streams : is hand-seining sufficient?

Unprecedented threats to natural ecosystems mean that accurate quantification of biodiversity is a priority, particularly in the tropics which are underrepresented in monitoring schemes. Data from a freshwater fish assemblage in Trinidad were used to evaluate the effectiveness of hand-seining as a survey method in tropical streams. We uncovered large differences in species detectability when hand-seining was used alone, in comparison with when hand-seining and electrofishing were used together. The addition of electrofishing increased the number of individuals caught threefold, and increased the biomass fivefold. Some species were never detected using hand-seining, resulting in significant underestimates of species richness; rarefaction curves suggest that even when hand-seining effort increases, species richness is still underestimated. Diversity indices (Shannon and Simpson index) reveal that diversity was also significantly lower for hand-seined samples. Furthermore, the results of multivariate analyses investigating assemblage structure also differed significantly depending on whether they were based on hand-seined data alone, or a combination of hand-seining and electrofishing. Despite the extra equipment and maintenance required, these findings underline the value of including electrofishing when sampling tropical freshwater streams.

From species to communities : the signature of recreational use on a tropical river ecosystem

Abstract Disturbance can impact natural communities in multiple ways. However, there has been a tendency to focus on single indicators of change when examining the effects of disturbance. This is problematic as classical diversity measures, such as Shannon and Simpson indices, do not always detect the effects of disturbance. Here, we instead take a multilevel, hierarchical approach, looking for signatures of disturbance in the capacity and diversity of the community, and also in allocation and demography at the population level. Using recreational use as an example of disturbance, and the freshwater streams of Trinidad as a model ecosystem, we repeatedly sampled the fish communities and physical parameters of eight pairs of recreational and nonrecreational sites every 3 months over a 28‐month period. We also chose the Trinidadian guppy (Poecilia reticulata) as the subject of our population‐level analyses. Regression tree analysis, together with analysis of deviance, revealed that community capacity and community species richness were greater at sites with higher levels of recreational use. Interestingly, measures of community diversity that took into account the proportional abundance of each species were not significantly associated with recreational use. Neither did we find any direct association between recreational use and proportion of guppy biomass in the community. However, population‐level differences were detected in the guppy: Sex ratio was significantly more female‐biased at more disturbed sites. Our findings emphasize the importance of considering multiple levels when asking how disturbance impacts a community. We advocate the use of a multilevel approach when monitoring the effects of disturbance, and highlight gaps in our knowledge when it comes to interpreting these effects.

Post-mortem examination and sampling of African flamingos (Phoenicopteridae) under field conditions

Recent largely unexplained deaths in African flamingos have prompted the need for standard, reproducible methods for the post-mortem examination of these birds, for the taking of samples and for the recording of findings. Here we describe suitable techniques and present three distinct protocols for field-based post-mortem examination of flamingos that can be employed flexibly, depending on the circumstances, by veterinarians and non-professionals alike. The adoption of these protocols is strongly recommended to improve standardisation of data and sample collection, which will ultimately enhance our understanding of the causes of mortality in African flamingos.

Gradients in predation risk in a tropical river system

Abstract The importance of predation risk as a key driver of evolutionary change is exemplified by the Northern Range in Trinidad, where research on guppies living in multiple parallel streams has provided invaluable insights into the process of evolution by natural selection. Although Trinidadian guppies are now a textbook example of evolution in action, studies have generally categorized predation as a dichotomous variable, representing high or low risk. Yet, ecologists appreciate that community structure and the attendant predation risk vary substantially over space and time. Here, we use data from a longitudinal study of fish assemblages at 16 different sites in the Northern Range to quantify temporal and spatial variation in predation risk. Specifically we ask: 1) Is there evidence for a gradient in predation risk? 2) Does the ranking of sites (by risk) change with the definition of the predator community (in terms of species composition and abundance currency), and 3) Are site rankings consistent over time? We find compelling evidence that sites lie along a continuum of risk. However, site rankings along this gradient depend on how predation is quantified in terms of the species considered to be predators and the abundance currency is used. Nonetheless, for a given categorization and currency, rankings are relatively consistent over time. Our study suggests that consideration of predation gradients will lead to a more nuanced understanding of the role of predation risk in behavioral and evolutionary ecology. It also emphasizes the need to justify and report the definition of predation risk being used.

A holistic approach to fieldwork through balanced reflective practice

Reflective practice is well-established as a tool for practitioner development in areas such as nursing, social work and education. Reflection involves the integration of theoretical constructs and practical action; therefore it seems somewhat ironic that there is little written on reflective practice within the natural sciences – where theory and action are often juxtaposed. This paper attempts to address this gap through examining biological fieldwork in relation to a balanced system of reflection that embraces the cognitive, psychomotor, affective and conative aspects of practice. A model of reflective practice that asks practitioners to log their reflections against these four domains was applied to a biodiversity survey of tropical mountain streams in Trinidad. It was found that there is clear evidence that biological fieldwork can embrace a reflective methodology and that reflective practice can be used in fieldwork as a tool for making explicit that which is already implicit. A holistic vision of fieldwork is sketched out here, where the introduction of a balanced model of reflective practice can support an approach that moves beyond the consideration of the environment and the researcher as two separate entities and, instead, considers the relationship between environment and researcher.

Forced monogamy in a multiply mating species does not impede colonisation success.

BackgroundThe guppy (Poecilia reticulata) is a successful invasive species. It is also a species that mates multiply; previous studies have demonstrated that this strategy carries fitness benefits. Guppies are routinely introduced to tanks and troughs in regions outside their native range for mosquito-control purposes, and often spread beyond these initial confines into natural water bodies with negative ecological consequences. Here, using a mesocosm set up that resembles the containers into which single guppies are typically introduced for mosquito control, we ask whether singly-mated females are at a disadvantage, relative to multiply-mated females, when it comes to founding a population. Treatments were monitored for one year.ResultsA key finding was that mating history did not predict establishment success, which was 88% in both treatments. Furthermore, analysis of behavioural traits revealed that the descendants of singly-mated females retained antipredator behaviours, and that adult males showed no decrease in courtship vigour. Also, we detected no differences in behavioural variability between treatments.ConclusionsThese results suggest that even when denied the option of multiple mating, singly-mated female guppies can produce viable populations, at least at the founder stage. This may prove to be a critical advantage in typical introduction scenarios where few individuals are released into enclosed water bodies before finding their way into natural ecosystems.

Individual variation in reproductive behaviour is linked to temporal heterogeneity in predation risk

Variation in predation risk is a major driver of ecological and evolutionary change, and, in turn, of geographical variation in behaviour. While predation risk is rarely constant in natural populations, the extent to which variation in predation risk shapes individual behaviour in wild populations remains unclear. Here, we investigated individual differences in reproductive behaviour in 16 Trinidadian guppy populations and related it to the observed variation in predator biomass each population experienced. Our results show that high heterogeneity in predator biomass is linked to individual behavioural diversification. Increased within-population heterogeneity in predator biomass is also associated with behavioural polymorphism. Some individuals adjust the frequency of consensual mating behaviour in response to differences in sex ratio context, while others display constantly at elevated frequencies. This pattern is analogous to a ‘live fast, die young’ pace-of-life syndrome. Notably, both high and low mean differences in predator biomass led to a homogenization of individual frequency of consensual mating displays. Overall, our results demonstrate that individual behavioural variation is associated with heterogeneity in predator biomass, but not necessarily with changes in mean values of predator biomass. We suggest that heterogeneity in predator biomass is an informative predictor of adaptive responses to changes in biotic conditions.