An Evaluation of Prior Residency and Habitat Effects on the Persistence of Settling Reef Fishes

<p>Both habitat complexity and competitive interactions can shape patterns of distribution and abundance of species. I evaluated the separate and joint effects of competitive interactions and habitat complexity on the survival of young fishes (Family Labridae) on coral reefs. First, I developed (in Chapter 2) a quantitative approach to evaluate potential resource (i.e., niche) overlap among groups of co-occurring species. Using appropriate transformations and probability models, I show that different types of data (e.g., categorical, continuous, count or binary data, as well as electivity scores) give rise to a standard measure of niche overlap, with the overlap statistic between two species defined as the overlapping area between the distributions for each species. Measurements derived from different types of data can be combined into a single multivariate analysis of niche overlap by averaging over multiple axes. I then describe null model permutation tests that differentiate between species occupying similar and different niches within my unified indices. I then implemented this approach (in Chapter 3) to evaluate potential habitat overlap among eight species of wrasse (Gomphosus varius, Halichoeres hortulanus, H. trimaculatus, Pseudocheilinus hexataenia, Scarus sordidus, Stethojulis bandanensis, Thalassoma hardwicke and T. quinquevittatum), and used these results to inform my subsequent field experiments. In a field assay, I identified the presence of T. quinquevittatum as having the greatest negative effect on survival of transplanted T. hardwicke from a suite of three candidate species which were most similar in habitat use to T. hardwicke (the other two candidate species were G. varius and P. hexataenia). In a subsequent field experiment, I tested how competition with T. quinquevittatum and structural refuge interact to influence the postsettlement survival of T. hardwicke. Competition with T. quinquevittatum and structural refuge both altered the survival of T. hardwicke, although their effects were not interactive, indicating that structural complexity did not mitigate the negative effects of competition. Survival of T. hardwicke was 2.3 times greater in treatments without T. quinquevittatum relative to those with T. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to treatments without structural refuge. Thalassoma hardwicke and T. quinquevittatum often enter reef communities asynchronously, resulting in competitive pressures faced by earlyarriving individuals that potentially differ from those experienced by late-arriving individuals. In a series of field experiments, I investigated whether the strength of intra-cohort competitive interactions between recent T. hardwicke and T. quinquevittatum settlers were dependent upon the sequence and temporal separation of their arrival into communities. Survival rates for both species were greatest in the absence of competitors, but when competitors were present, survival rates were maximized when competitors arrived simultaneously. Survival rates declined as each species entered the community progressively later than its competitor. Further, reversals in the sequence of arrival reversed competitive outcomes. Results provide empirical evidence for competitive lotteries in the maintenance of species diversity in demographically open marine systems, while also highlighting the importance of temporal variation in the direction and magnitude of interaction strengths. To further our understanding of how timing of arrival influences interaction strengths, I tested whether increasing the availability of complex habitat attenuates or enhances timing-of-arrival effects. Results from this field experiment indicated that aggression by early-arriving individuals towards late-arriving individuals increased as arrival times diverged. When aggression was weak, subordinate individuals were not displaced from complex habitat. Experimental increases in the availability of complex habitat resulted in increased survival of subordinates, presumably by disrupting predation pressure. However, when aggression was intense, competitive subordinates were displaced from complex habitat (regardless of the amount of complex habitat available), and this likely increased their exposure to predators. Overall, the experimental and observational components of this thesis emphasise heterogeneity in competitive environments experienced by recently settled reef fishes. These results highlight the important role that priority effects and habitat complexity play in determining the persistence of reef fish settlers, and illustrate how ecological contexts can add considerable variation to realised interaction strengths.</p>

An Evaluation of Prior Residency and Habitat Effects on the Persistence of Settling Reef Fishes

<p>Both habitat complexity and competitive interactions can shape patterns of distribution and abundance of species. I evaluated the separate and joint effects of competitive interactions and habitat complexity on the survival of young fishes (Family Labridae) on coral reefs. First, I developed (in Chapter 2) a quantitative approach to evaluate potential resource (i.e., niche) overlap among groups of co-occurring species. Using appropriate transformations and probability models, I show that different types of data (e.g., categorical, continuous, count or binary data, as well as electivity scores) give rise to a standard measure of niche overlap, with the overlap statistic between two species defined as the overlapping area between the distributions for each species. Measurements derived from different types of data can be combined into a single multivariate analysis of niche overlap by averaging over multiple axes. I then describe null model permutation tests that differentiate between species occupying similar and different niches within my unified indices. I then implemented this approach (in Chapter 3) to evaluate potential habitat overlap among eight species of wrasse (Gomphosus varius, Halichoeres hortulanus, H. trimaculatus, Pseudocheilinus hexataenia, Scarus sordidus, Stethojulis bandanensis, Thalassoma hardwicke and T. quinquevittatum), and used these results to inform my subsequent field experiments. In a field assay, I identified the presence of T. quinquevittatum as having the greatest negative effect on survival of transplanted T. hardwicke from a suite of three candidate species which were most similar in habitat use to T. hardwicke (the other two candidate species were G. varius and P. hexataenia). In a subsequent field experiment, I tested how competition with T. quinquevittatum and structural refuge interact to influence the postsettlement survival of T. hardwicke. Competition with T. quinquevittatum and structural refuge both altered the survival of T. hardwicke, although their effects were not interactive, indicating that structural complexity did not mitigate the negative effects of competition. Survival of T. hardwicke was 2.3 times greater in treatments without T. quinquevittatum relative to those with T. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to treatments without structural refuge. Thalassoma hardwicke and T. quinquevittatum often enter reef communities asynchronously, resulting in competitive pressures faced by earlyarriving individuals that potentially differ from those experienced by late-arriving individuals. In a series of field experiments, I investigated whether the strength of intra-cohort competitive interactions between recent T. hardwicke and T. quinquevittatum settlers were dependent upon the sequence and temporal separation of their arrival into communities. Survival rates for both species were greatest in the absence of competitors, but when competitors were present, survival rates were maximized when competitors arrived simultaneously. Survival rates declined as each species entered the community progressively later than its competitor. Further, reversals in the sequence of arrival reversed competitive outcomes. Results provide empirical evidence for competitive lotteries in the maintenance of species diversity in demographically open marine systems, while also highlighting the importance of temporal variation in the direction and magnitude of interaction strengths. To further our understanding of how timing of arrival influences interaction strengths, I tested whether increasing the availability of complex habitat attenuates or enhances timing-of-arrival effects. Results from this field experiment indicated that aggression by early-arriving individuals towards late-arriving individuals increased as arrival times diverged. When aggression was weak, subordinate individuals were not displaced from complex habitat. Experimental increases in the availability of complex habitat resulted in increased survival of subordinates, presumably by disrupting predation pressure. However, when aggression was intense, competitive subordinates were displaced from complex habitat (regardless of the amount of complex habitat available), and this likely increased their exposure to predators. Overall, the experimental and observational components of this thesis emphasise heterogeneity in competitive environments experienced by recently settled reef fishes. These results highlight the important role that priority effects and habitat complexity play in determining the persistence of reef fish settlers, and illustrate how ecological contexts can add considerable variation to realised interaction strengths.</p>

Emerging dynamics from high-resolution spatial numerical epidemics

Simulating nationwide realistic individual movements with a detailed geographical structure can help optimize public health policies. However, existing tools have limited resolution or can only account for a limited number of agents. We introduce Epidemap, a new framework that can capture the daily movement of more than 60 million people in a country at a building-level resolution in a realistic and computationally efficient way. By applying it to the case of an infectious disease spreading in France, we uncover hitherto neglected effects, such as the emergence of two distinct peaks in the daily number of cases or the importance of local density in the timing of arrival of the epidemic. Finally, we show that the importance of super-spreading events strongly varies over time.

The nesting ecology and postembryonic development of the Baikal white wagtail Motacilla alba baicalensis

The goal of the paper is to identify the features of the breeding ecology of the Motacilla alba baicalensis in the Baikal region and Transbaikalia. The nesting ecology study deliverable of the Motacilla alba baicalensis in the Baikal region and Transbaikalia showed that this subspecies, unlike other forms, is more synanthropic, more than 95% of populations live in localities and other anthropogenic habitats, and only 23% of populations inhabit natural biotopes. At the same time, the Motacilla alba baicalensis in the region prefers small rural settlements and livestock camps in open landscapes near reservoirs. When the Motacilla alba baicalensis builds nests, like other subspecies, it is quite plastic and easily finds shelter in various anthropogenic and natural biotopes. The higher nesting efficiency of this subspecies indicates its wide opportunities to develop anthropogenic landscapes. Due to the short favorable nesting period, most pairs manage to hatch chicks once, but only a small number of pairs manage to raise chicks twice a season. A comparison of the nesting ecology of the Motacilla alba baicalensis with other forms of the Northern Eurasian species did not reveal any fundamental differences. The differences relate to the phenology of different stages of the breeding season, as well as the timing of arrival and departure of birds.

Spinal motoneuron firing properties mature from rostral to caudal during post-natal development of the mouse

Altricial mammals are born with immature nervous systems comprised of circuits that do not yet have the neuronal properties and connectivity required to produce future behaviours. During the critical period of post-natal development, neuronal properties are tuned to participate in functional circuits. In rodents, cervical motoneurons are born prior to lumbar motoneurons, and spinal cord development follows a sequential rostro-caudal sequence. Here we asked whether birth order is reflected in the post-natal development of electrophysiological properties. We show that motoneurons of both segments have similar properties at birth and follow the same developmental profile, with maximal firing increasing and excitability decreasing into the 3rd post-natal week. However, these maturative processes occur in cervical prior to lumbar motoneurons, correlating to the timing of arrival of descending systems. These results suggest that motoneuron properties do not mature by cell autonomous mechanisms alone, but rather depend on developing descending and spinal circuits.

The exotic species Senecio inaequidens pays the price for arriving late in temperate European grassland communities

The exotic South African ragwort (Senecio inaequidens DC.) rapidly spread across Central Europe after its introduction, but we still do not know to what extent its timing of arrival in a plant community (i.e. before or after natives) and the composition of the native community being invaded affect (1) its capacity to invade a European grassland, (2) the performance of the native species, and (3) the direction and strength of priority effects. In a greenhouse experiment, we manipulated the timing of arrival of the exotic species (Senecio) and the composition of the native community to test the influence of these factors on the productivity and N content of exotic and native species. We also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late in the community. The establishment success of Senecio strongly depended on its timing of arrival in a grassland community. Senecio benefited more from arriving early than did the natives. The presence of legumes in the community did not favour invasion by Senecio. When natives arrived later than Senecio, however, priority effects were weaker when legumes were part of the native community. Our results showed that inhibitory priority effects created by natives can lower the risk of invasion by Senecio. An early arrival of this species at a site with low native species abundance is a scenario that could favour invasion.

Timing of arrival in the breeding area is repeatable and affects reproductive success in a non-migratory population of blue tits

ABSTRACTEvents in one part of the annual cycle often affect the performance (and subsequently fitness) of individuals later in the season (carry-over effects). An important aspect of this relates to the timing of activities. For example, many studies on migratory birds have shown that relatively late spring arrival in the breeding area reduces both the likelihood of getting a mate or territory and reproductive success.In contrast, relatively little is known about movements of individuals in non-migratory populations during the non-breeding season. Few studies have investigated the timing of arrival at the breeding area in such species, possibly due to the assumption that most individuals remain in the area during the non-breeding season.In this study, we used four years of data from a transponder-based automated recording system set up in a non-migratory population of blue tits (Cyanistes caeruleus) to describe individual variation in arrival at the breeding site. We investigated whether this variation can be explained by individual characteristics (sex, body size, or status), and we assessed its effect on aspects of reproductive success in the subsequent breeding season.We found substantial variation in arrival date and demonstrate that this trait is individual-specific (repeatable). Females arrived later than males, but the arrival dates of social pair members were more similar than expected by chance. Arrival predicted both whether an individual would end up breeding that season, and several aspects of its breeding success.Our study suggests that non-migratory species show a form of incipient migration behaviour in that they leave the breeding area during the non-breeding season. We conclude that the timing of pre-breeding events, in particular arrival date, may be an overlooked, but important, fitness-relevant trait in non-migratory species.