The interactive effects of predators, resources, and disturbance on freshwater snail populations from the Everglades

The origins of population dynamics depend on interplay between abiotic and biotic factors; the relative importance of each changing across space and time. Predation is a central feature of ecological communities that removes individuals (consumption) and alters prey traits (non-consumptive). Resource quality mitigates non-consumptive predator effects by stimulating growth and reproduction. Disturbance resets predator-prey interactions by removing both. I integrate experiments, time-series analysis, and performance trials to examine the relative importance of these on the population dynamics of a snail species by studying a variety of their traits. A review of ninety-three published articles revealed that snail abundance was much less in the Everglades and similar ecosystems compared to all other freshwater ecosystems considered. Separating consumptive from non-consumptive (cues) predator effects at different phosphorous levels with an experiment determined that phosphorous stimulated, but predator cues inhibited snail growth (34% vs. 23%), activity (38% vs. 53%), and reproductive effort (99% vs. 90%) compared to controls. Cues induced taller shells and smaller openings and moved to refugia where they reduced periphyton by 8%. Consumptive predator effects were minor in comparison. In a reciprocal transplant cage experiment along a predator cue and phosphorous gradient created by a canal, snails grew 10% faster and produced 37% more eggs far from the canal (fewer cues) when fed phosphorous-enriched periphyton from near the canal. Time-series analysis at four sites and predator performance trials reveal that phosphorous-enriched regions support larger snail populations, seasonal drying removes snails at all sites, crayfish negatively affect populations in enriched regions, and molluscivorous fish consume snails in the wet season. Combining these studies reveals interplay between resources, predators, and seasonality that limit snail populations in the Everglades and lead to their low abundance compared to other freshwater ecosystems. Resource quality is emerging as the critical factor because improving resources profoundly improved growth and reproduction; seasonal drying and predation become important at times and places. This work contributes to the general understanding in ecology of the relative importance of different factors that structure populations and provides evidence that bolsters monitoring efforts to assess the Comprehensive Everglades Restoration Plan that show phosphorous enrichment is a major driver of ecosystem change.

Disturbance frequency and community structure in a twenty-five year intervention study

Models of community regulation commonly incorporate gradients of disturbance inversely related to the role of biotic interactions in regulating intermediate trophic levels. Higher trophic-level organisms are predicted to be more strongly limited by intermediate levels of disturbance than are the organisms they consume. We used a manipulation of the frequency of hydrological disturbance in an intervention analysis to examine its effects on small-fish communities in the Everglades, USA. From 1978 to 2002, we monitored fishes at one long-hydroperiod (average 350 days) and at one short-hydroperiod (average 259 days; monitoring started here in 1985) site. At a third site, managers intervened in 1985 to diminish the frequency and duration of marsh drying. By the late 1990s, the successional dynamics of density and relative abundance at the intervention site converged on those of the long-hydroperiod site. Community change was manifested over 3 to 5 years following a dry-down if a site remained inundated; the number of days since the most recent drying event and length of the preceding dry period were useful for predicting population dynamics. Community dissimilarity was positively correlated with the time since last dry. Community dynamics resulted from change in the relative abundance of three groups of species linked by life-history responses to drought. Drought frequency and intensity covaried in response to hydrological manipulation at the landscape scale; community-level successional dynamics converged on a relatively small range of species compositions when drought return-time extended beyond 4 years. The density of small fishes increased with diminution of drought frequency, consistent with disturbance-limited community structure; less-frequent drying than experienced in this study (i.e., longer return times) yields predator-dominated regulation of small-fish communities in some parts of the Everglades.

Data compilation on the biological response to ocean acidification: environmental and experimental context of data sets and related literature

The exponential growth of studies on the biological response to ocean acidification over the last few decades has generated a large amount of data. To facilitate data comparison, a data compilation hosted at the data publisher PANGAEA was initiated in 2008 and is updated on a regular basis (doi:10.1594/PANGAEA.149999). By January 2015, a total of 581 data sets (over 4 000 000 data points) from 539 papers had been archived. Here we present the developments of this data compilation five years since its first description by Nisumaa et al. (2010). Most of study sites from which data archived are still in the Northern Hemisphere and the number of archived data from studies from the Southern Hemisphere and polar oceans are still relatively low. Data from 60 studies that investigated the response of a mix of organisms or natural communities were all added after 2010, indicating a welcomed shift from the study of individual organisms to communities and ecosystems. The initial imbalance of considerably more data archived on calcification and primary production than on other processes has improved. There is also a clear tendency towards more data archived from multifactorial studies after 2010. For easier and more effective access to ocean acidification data, the ocean acidification community is strongly encouraged to contribute to the data archiving effort, and help develop standard vocabularies describing the variables and define best practices for archiving ocean acidification data.

Effects of seasonally varying temperature and salinity on the dynamics of sea lice (Lepeophtheirus salmonis)

Sea lice (Lepeophtheirus salmonis) are an economically significant parasite in salmonid aquaculture. They exhibit temperature-dependent development rates and salinity-dependent mortality, which can greatly impact sea lice population dynamics, but no deterministic models have incorporated these seasonal variables. To understand how seasonality affects sea lice population dynamics, I derive a delay differential equation model with temperature and salinity dependence. I find that peak reproductive output in Newfoundland and British Columbia differs by four months. A sensitivity analysis shows sea lice abundance is most sensitive to variation in mean annual water temperature and salinity, whereas it is lease sensitive to infection rate. Additionally, I investigate the effects of production cycle timing on sea lice management and find that optimal production cycle start times are between the 281st and 337th days of the year in Newfoundland. I also demonstrate that adjusting follow-up treatment timing in response to temperature can improve treatment regimes. My results suggest that effective sea lice management requires consideration of local temperature and salinity patterns.

Investigations on the Chilean kelp crab Taliepus dentatus

Physiological responses of larval stages can differ from those of the adults, affecting key ecological processes. Therefore, developing a mechanistic understanding of larval responses to environmental conditions is essential vis-à-vis climate change. We studied the thermal tolerance windows, defined by lower and upper pejus (Tp) and critical temperatures (Tc), of zoea I, II, and megalopa stages of the Chilean kelp crab Taliepus dentatus. Tp limits determine the temperature range where aerobic scope is maximal and functioning of the organism is unrestrained and were estimated from direct observations of larval activity. Tc limits define the transition from aerobic to anaerobic metabolism, and were estimated from the relationship between standard metabolic rate and temperature. Zoea I showed the broadest, Zoea II an intermediate, and megalopae the narrowest tolerance window (Tp). Optimum performance in megalopae was limited to Tp between 11 and 15°C, while their Tc ranged between 7 and 19°C. Although Tc may be seldom encountered by larvae, the narrower Tp temperatures can frequently expose larvae to unfavorable conditions that can drastically constrain their performance. Temperatures beyond the Tp range of megalopae have been observed in most spring and summer months in central Chile, and can have important consequences for larval swimming performance and impair their ability to avoid predators or settle successfully. Besides the well-documented effects of temperature on development time, variability in field temperatures beyond Tp can affect performance of particular larval stages, which could drive large-scale variability in recruitment and population dynamics of T. dentatus and possibly other invertebrate species.

Intraspecific Behavioural Diversity in a Freshwater Zooplankton: A study of the fitness consequences of vertical migration behaviour for distinct morphs of Daphnia pulicaria

The literature on niche separation and coexistence between species is large, but there is widespread variation in behavioural strategy between individuals of the same species that has received much less attention. Understanding what maintains this diversity is important because intraspecific behavioural diversity can affect population dynamics and community interactions. Multiple behavioural strategies can arise either as phenotype-dependent ‘conditional strategies’, where phenotypic variation causes individuals to adopt different strategies for optimizing fitness, or as internally-independent ‘alternative strategies’, where multiple fitness peaks exist for individuals and strategic ‘choice’ remains plastic. Though intraspecific variation in stable phenotypes is known to maintain intraspecific behavioural diversity through conditional strategies, when internal conditions are highly plastic or reversible, it is not clear whether individual behaviours are maintained as conditional strategies, or as alternative strategies of equal fitness. In this study, I combine an observational and experimental approach to identify the likely mechanisms maintaining behavioural diversity between hemoglobin-rich and hemoglobin-poor morphs in a natural population of Daphnia pulicaria. In Round Lake, individuals with low hemoglobin migrate daily from the hypolimnion to the epilimnion, whereas individuals with high hemoglobin remain in the hypolimnion. Using high-resolution depth and time sampling, I discovered behavioural diversity both within and among hemoglobin phenotypes. I tested the role of hemoglobin phenotype in maintaining behavioural diversity using automated migration robots that move individuals across the natural environmental gradients in the lake. By measuring the fitness of each morph undergoing either a natural migration behaviour, or the migration of the opposite morph, I found that the fitness of hemoglobin rich and poor morphs in their natural behaviour does not differ, but that Hb-rich individuals can obtain equal fitness from either behaviour, while Hb-poor morphs suffer substantial drops in survivorship in the alternate migration behaviour. Thus, migration behaviour in this system exists as a conditional strategy for some individuals, and as alternative strategies of equal fitness for others. The results of this study suggest that individual limits in the expression of highly flexible internal conditions can reinforce intraspecific behavioural diversity. Few studies have measured the fitness consequences of switching migration strategies and this study provides a rare example in the field.

Growth and shrinkage in Antarctic krill Euphausia superba is sex-dependent

ABSTRACT: The ability of Antarctic krill Euphausia superba Dana to withstand the overwintering period is critical to their success. Laboratory evidence suggests that krill may shrink in body length during this time in response to the low availability of food. Nevertheless, verification that krill can shrink in the natural environment is lacking because winter data are difficult to obtain. One of the few sources of winter krill population data is from commercial vessels. We examined length-frequency data of adult krill (>35 mm total body length) obtained from commercial vessels in the Scotia-Weddell region and compared our results with those obtained from a combination of science and commercial sampling operations carried out in this region at other times of the year. Our analyses revealed body-length shrinkage in adult females but not males during overwinter, based on both the tracking of modal size classes over seasons and sex-ratio patterns. Other explanatory factors, such as differential mortality, immigration and emigration, could not explain the observed differences. The same pattern was also observed at South Georgia and in the Western Antarctic Peninsula. Fitted seasonally modulated von Bertalanffy growth functions predicted a pattern of overwintering shrinkage in all body-length classes of females, but only stagnation in growth in males. This shrinkage most likely reflects morphometric changes resulting from the contraction of the ovaries and is not necessarily an outcome of winter hardship. The sex-dependent changes that we observed need to be incorporated into life cycle and population dynamic models of this species, particularly those used in managing the fishery. KEY WORDS: Southern Ocean · Population dynamics · Production · Life cycle · Fishery

Growth and shrinkage in Antarctic krill Euphausia superba is sex-dependent

ABSTRACT: The ability of Antarctic krill Euphausia superba Dana to withstand the overwintering period is critical to their success. Laboratory evidence suggests that krill may shrink in body length during this time in response to the low availability of food. Nevertheless, verification that krill can shrink in the natural environment is lacking because winter data are difficult to obtain. One of the few sources of winter krill population data is from commercial vessels. We examined length-frequency data of adult krill (>35 mm total body length) obtained from commercial vessels in the Scotia-Weddell region and compared our results with those obtained from a combination of science and commercial sampling operations carried out in this region at other times of the year. Our analyses revealed body-length shrinkage in adult females but not males during overwinter, based on both the tracking of modal size classes over seasons and sex-ratio patterns. Other explanatory factors, such as differential mortality, immigration and emigration, could not explain the observed differences. The same pattern was also observed at South Georgia and in the Western Antarctic Peninsula. Fitted seasonally modulated von Bertalanffy growth functions predicted a pattern of overwintering shrinkage in all body-length classes of females, but only stagnation in growth in males. This shrinkage most likely reflects morphometric changes resulting from the contraction of the ovaries and is not necessarily an outcome of winter hardship. The sex-dependent changes that we observed need to be incorporated into life cycle and population dynamic models of this species, particularly those used in managing the fishery. KEY WORDS: Southern Ocean · Population dynamics · Production · Life cycle · Fishery

Fisheries stocks from an ecological perspective: Disentangling ecological connectivity from genetic interchange

The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for fisheries science. Methods for delimiting stocks have advanced considerably over recent years, including genetic, telemetric, tagging, geochemical and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and/or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can be delimited as management units if there is limited exchange during recruitment or via migration in most years. From a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

Fisheries stocks from an ecological perspective: Disentangling ecological connectivity from genetic interchange

The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for fisheries science. Methods for delimiting stocks have advanced considerably over recent years, including genetic, telemetric, tagging, geochemical and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and/or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can be delimited as management units if there is limited exchange during recruitment or via migration in most years. From a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

Dynamique d’une population faunique en expansion sous différents scénarios climatiques : le dindon sauvage (Meleagris gallopavo)

Les changements climatiques récents ont mené à l’expansion de la répartition de plusieurs espèces méridionales, mais ont aussi causé l’extinction locale d’espèces se retrouvant à la limite de leur tolérance environnementale. Ces populations en expansion peuvent favoriser différentes stratégies d’histoire de vie en répondant à différents facteurs limitants. Dans cette thèse, je vise à déterminer et quantifier l’effet du climat et des évènements extrêmes sur le cycle de vie complet d’une espèce en expansion (le dindon sauvage) pour comprendre les changements au niveau populationnel ainsi que les mécanismes impliqués dans l’expansion de la distribution d’une espèce. J’ai défini les évènements extrêmes de pluie, d’épaisseur de neige au sol et de température, comme un évènement dont la fréquence est plus rare que le 10e et 90e percentile. En utilisant l’approche « Measure-Understand-Predict » (MUP), j’ai tout d’abord suivi trois populations le long d’un gradient latitudinal de sévérité hivernale pour mesurer l’effet de variables météorologiques sur la dynamique des populations. La survie des dindons sauvages diminuait drastiquement lorsque l’accumulation de neige au sol dépassait 30 cm pour une période de 10 jours et diminuait également avec la température. Au printemps, la persistance de la neige affectait négativement le taux d’initiation de la nidification et l’augmentation de la pluie diminuait la survie des nids. Dans une deuxième étape, j’ai examiné l’impact des évènements climatiques extrêmes et des processus démographiques impliqués dans l’expansion du dindon, liés à la théorie des histoires de vie pour comprendre la relation entre la dynamique de ces populations en expansions avec le climat. J’ai démontré que la fréquence des évènements extrêmes hivernaux et, d’une façon moins importante, les évènements extrêmes estivaux limitaient l’expansion nordique des dindons sauvages. J’ai appuyé, à l’aide de données empiriques et de modélisation, les hypothèses de la théorie classique des invasions biologiques en montrant que les populations en établissement priorisaient les paramètres reproducteurs tandis que la survie adulte était le paramètre démographique affectant le plus la dynamique des populations bien établies. De plus, les populations les plus au nord étaient composées d’individus plus jeunes ayant une espérance de vie plus faible, mais avaient un potentiel d’accroissement plus élevé que les populations établies, comme le suggère cette théorie. Finalement, j’ai projeté l’impact de la récolte sur la dynamique des populations de même que le taux de croissance de cette espèce en utilisant les conditions climatiques futures projetées par les modèles de l’IPCC. Les populations en établissement avaient un taux de récolte potentiel plus élevé, mais la proportion de mâles adultes, possédant des caractéristiques recherchées par les chasseurs, diminuait plus rapidement que dans les populations établies. Dans le futur, la fréquence des évènements extrêmes de pluie devrait augmenter tandis que la fréquence des évènements extrêmes de température hivernale et d’accumulation de neige au sol devraient diminuer après 2060, limitant probablement l’expansion nordique du dindon sauvage jusqu’en 2100. Cette thèse améliore notre compréhension des effets météorologiques et du climat sur l’expansion de la répartition des espèces ainsi que les mécanismes démographiques impliqués, et nous a permis de prédire la probabilité de l’expansion nordique de la répartition du dindon sauvage en réponse aux changements climatiques.

Infection dynamics of Marteilia refringens in flat oyster Ostrea edulis and copepod Paracartia grani in a claire pond of Marennes-Oleron Bay

The protozoan parasite Marteilia refringens has been partly responsible for the severe decrease in the production of the European flat oyster Ostrea edulis Linnaeus in France since the 1970s. The calanoid copepod Paracartia grani Sars was recently found to be a host for M refringens in French shallow-water oyster ponds ('claires'). This study reconsidered M refringens transmission dynamics in the light of this finding, taking into account not only oyster infection dynamics and environmental factors but also data concerning the copepod host. P. grani population dynamics in the claire under study revealed that this species is the dominant planktonic copepod in this confined ecosystem. During winter, M refringens overwintered in O. edulis, with P. grani existing only as resting eggs in the sediment. The increase in temperature in spring controlled and synchronized both the release of M refringens sporangia in the oyster feces, and the hatching of the benthic resting eggs of the copepod. Infection of oysters by M refringens was limited to June, July and August, coinciding with (1) the highest temperature recorded in the claire, and (2) the highest abundance of P. grani. PCR detection of M refringens in P. grani during the summer period was linked to the release of parasite sporangia by the oyster. Our results are supported by previous results on the effective transmission of this parasite from the oyster to the copepod.

Early post-fledgling survival in a fragmented population of a tropical cooperative breeding passerine

During the last years tropical forest has been a target of intense study especially due to its recent big scale destruction. Although a lot still needs to be explored, we start realizing how negative can the impact of our actions be for the ecosystem. Subsequently, the living community have been developing strategies to overcome this problem avoiding bottlenecks or even extinctions. Cooperative breeding (CB) has been recently pointed out as one of those strategies. CB is a breeding system where more than two individuals raise one brood. In most of the cases, extra individuals are offspring that delay their dispersal and independent breeding what allows them to help their parents raising their siblings in the subsequent breeding season. Such behavior is believed to be due, per example, to the lack of mates or breeding territories (ecological constraints hypothesis), a consequence of habitat fragmentation and/or disturbance. From this point, CB is easily promoted by a higher reproductive success of group vs pairs or single individuals. Accordingly, during this thesis I explore the early post-fledging survival of a cooperative breeding passerine, namely the impact of individual/habitat quality in its survival probability during the dependence period of the chicks. Our study species is the Cabanis’s greenbul (Phyllastrephus cabanisi), a medium-sized, brownish passerine, classified within the Pycnonotidae family. It is found over part of Central Africa in countries such as Angola, Democratic Republic of the Congo, Mozambique and Kenya, inhabiting primary and secondary forests, as well as woodland of various types up to 2700m of altitude. Previous studies have concluded that PC is a facultative cooperative breeder. This study was conducted in Taita Hills (TH) at the Eastern Arc Mountains (EAM), a chain of mountains running from Southeast Kenya to the South of Tanzania. TH comprises an area of 430 ha and has been suffering intense deforestation reflecting 98% forest reduction over the last 200 years. Nowadays its forest is divided in fragments and our study was based in 5of those fragments. We access the post-fledging survival through radio-telemetry. The juvenile survey was done through the breeding females in which transmitters were placed with a leg-loop technique. Ptilochronology is consider to be the study of feather growth bars and has been used to study the nutritional state of a bird. This technique considers that the feather growth rate is positively proportional to the individual capability of ingesting food and to the food availability. This technique is therefore used to infer for individual/habitat quality. Survival was lowest during the first 5 days post-fledging representing 53.3%. During the next 15 days, risk of predation decreased with only 14.3% more deceased individuals. This represents a total of only 33% survived individuals in the end of the 50 days. Our results showed yet a significant positive relationship between flock size and post-fledging survival as well as between ptilochronology values and post-fledgling survival. In practice, these imply that on this population, as bigger the flock, as greater the post fledging survival and that good habitat quality or good BF quality, will lead to a higher juvenile survival rate. We believe that CB is therefore an adaptive behaviour to the lack of mates/breeding territory originated from the mass forest destruction and disturbance. Such results confirms the critical importance of habitat quality in the post-fledging survival and, for the first time, demonstrates how flock size influences the living probability of the juveniles and therefore how it impacts the (local) population dynamics of this species. In my opinion, future research should be focus in disentangle individual and habitat quality from each other and verify which relationship exist between them. Such study will allow us to understand which factor has a stronger influence in the post-fledging survival and therefore redirect our studies in that direction. In order to confirm the negative impact of human disturbance and forest fragmentation, it would be of major relevance to compare the reproductive strategies and reproductive success of populations living in intact forests and disturbed patches.

Predictive Models for Tomato Spotted Wilt Virus Spread Dynamics, Considering Frankliniella occidentalis Specific Life Processes as Influenced by the Virus

Several models have been studied on predictive epidemics of arthropod vectored plant viruses in an attempt to bring understanding to the complex but specific relationship between the three cornered pathosystem (virus, vector and host plant), as well as their interactions with the environment. A large body of studies mainly focuses on weather based models as management tool for monitoring pests and diseases, with very few incorporating the contribution of vector's life processes in the disease dynamics, which is an essential aspect when mitigating virus incidences in a crop stand. In this study, we hypothesized that the multiplication and spread of tomato spotted wilt virus (TSWV) in a crop stand is strongly related to its influences on Frankliniella occidentalis preferential behavior and life expectancy. Model dynamics of important aspects in disease development within TSWV-F. occidentalis-host plant interactions were developed, focusing on F. occidentalis' life processes as influenced by TSWV. The results show that the influence of TSWV on F. occidentalis preferential behaviour leads to an estimated increase in relative acquisition rate of the virus, and up to 33% increase in transmission rate to healthy plants. Also, increased life expectancy; which relates to improved fitness, is dependent on the virus induced preferential behaviour, consequently promoting multiplication and spread of the virus in a crop stand. The development of vector-based models could further help in elucidating the role of tri-trophic interactions in agricultural disease systems. Use of the model to examine the components of the disease process could also boost our understanding on how specific epidemiological characteristics interact to cause diseases in crops. With this level of understanding we can efficiently develop more precise control strategies for the virus and the vector.

What can exploratory modelling tell us about the ecobiology of European sea bass ( Dicentrarchus labrax ): a comprehensive overview

European sea bass, Dicentrarchus labrax, is a highly valuable species in Europe, both for aquaculture in the Mediterranean Sea and for commercial and recreational fisheries in the North East Atlantic Ocean. Subjected to increasing fishing pressure, the wild population has recently experienced significant recruitment fluctuation as well as a northward extension of its distribution area in the North Sea. While the nature of the ecological and/or physiological processes involved remains unresolved, ontogenetic habitat shifts and adult site fidelity could increase the species’ vulnerability to climate change and overfishing. As managers look for expert information to propose management scenarios leading to sustainable exploitation, exploratory modelling appears to be a cost-efficient approach to enhance the understanding of recruitment dynamics and the spatio-temporal scales over which fish populations function. A conceptual modelling framework and its specific data requirements are discussed to tackle some sound ecological questions regarding this species. We consequently provide an updated review of current knowledge on bass population structure, biology and ecology. This paper will hence be particularly valuable to develop spatially-explicit models of European sea bass dynamics under environmental and anthropogenic forcing. Knowledge gaps requiring further research efforts are also reported.