Reproductive Fluctuations Research Articles

Ecology and social behavior of the tamarisk gerbil Meriones tamariscinus: insights from long-term research in the wild and semi-natural environments.

The present review provides a compilation of the published data on the ecology and social behavior of tamarisk gerbils. Both field studies and direct observations under semi-natural conditions provide evidence that the tamarisk gerbil is a nocturnal herbivorous rodent that lives in highly seasonal habitats and displays seasonal fluctuations in reproduction and spatial organization. A typical feature of the tamarisk gerbils' spatial organization is higher mobility of males during the breeding season (as compared with the nonbreeding period) and formation of temporary aggregations of males competing for access to receptive females; the composition of these aggregations was variable and depended on the reproductive condition of the females. Females tend to occupy exclusive home ranges irrespective of their reproductive condition. The mating system of the species can be defined as scramble competition polygyny with some features of polygynandry and promiscuity. The tamarisk gerbil has distinct features of a solitary species and its social structure is primarily based on aggressive interactions or mutual avoidance of conspecifics resulting in a dominance hierarchy among males and site-dependent dominance among females during the breeding season. By the end of the breeding season, males become less mobile and occupy nearly exclusive home ranges, consistent with solitary living. The main features of the spatial and social organization of this species, which distinguish it from other solitary rodents, are the higher mobility of males and the formation of temporary multimale-multifemale aggregations during the breeding season. Overall, the data presented expand our understanding of socioecology of gerbils.

Targeting season and age for optimizing control of invasive rabbits

ABSTRACTThe effectiveness of invasive species control can be influenced by seasonal fluctuations in reproduction in response to environmental conditions. However, it is difficult to determine how demography and environmental conditions affect the efficacy of different control efforts from field trials alone. We incorporated an ontogenetic growth model into a hierarchical Bayesian mark‐recapture model to estimate age‐structured seasonal survival rates for European rabbits (Oryctolagus cuniculus) in Australia, based on a >15‐year data set. We integrated this demographic information into an individual‐based simulation model, which reproduces seasonal birth‐death processes, to test the effectiveness of pest‐management schemes that differed in intensity, specificity to age groups, and seasonal timing. Control measures that were simulated to affect only juveniles had a negligible effect on population size, whereas targeting subadults and adults led to considerable population declines when applied after the breeding season. Management that affected rabbits of all age groups caused significant population reductions. However, even repeated control efforts that caused 95% mortality each year only resulted in predictions of local population extirpation after an average of 119 calendar weeks in the absence of immigration. Our simulation study supports the use of pest rabbit control methods that account for demographic dynamics explicitly, and target those individuals with high reproductive potential. More broadly, we show that local and temporal population extirpation, or recovery, depends largely on the trade‐off between control intensity and frequency for species with recurrent population oscillations. © 2016 The Wildlife Society.

Limited Dispersal Drives Clustering and Reduces Coexistence by the Storage Effect.

Temporal variation can facilitate the coexistence of competitors through the temporal storage effect. However, this theoretical result was derived with the assumption that species have high dispersal rates. Here, I show that limited dispersal diminishes the storage effect in the classical lottery model. Populations become highly clustered during invasion, and population growth rates and extinction probabilities are functions of cluster size. I adopt the term "nucleation" from the physics literature to describe these characteristics. I developed approximations that incorporated nucleation to capture the spatiotemporal dynamics of the simulated model. Using analytical results from these approximations, I show that limited dispersal dampens asynchronous fluctuations in reproduction between species. This makes species appear to be more similar in their growth rate responses to the environment, thus reducing the potential for the storage effect. Theoretical results lead to simple rules relating average dispersal distances to relative reductions in potential coexistence. To demonstrate their use, I perform a preliminary analysis of two plant communities: tropical trees and desert annuals. In both communities, small-seeded species that disperse short distances on average have the strongest reductions in potential coexistence; species with wind- or animal-driven dispersal disperse farther distances, on average, and experience moderate or small reductions.

Reproductive toxicity of bisphenol A and cadmium in Potamopyrgus antipodarum and modulation of bisphenol A effects by different test temperature

An OECD initiative for the development of mollusc-based toxicity tests for endocrine disrupters and other chemicals has recommended three test species with respective test designs for further standardisation. Preparing a subsequent pre-validation study we performed a reproduction test with Potamopyrgus antipodarum, determining the concentration range of the selected test substances, bisphenol A (BPA) and cadmium (Cd). At 16 °C, the recommended test temperature, the number of embryos in the brood pouch was increased by BPA and decreased by Cd (NOEC: 20 μg BPA/L and 1 μg Cd/L). Coinstantaneous BPA tests at 7 °C and 25 °C demonstrated a temperature dependency of the response, resulting in lower NOECs (5 μg/L respectively). As expected, reproduction in control groups significantly varied depending on temperature. Additional observations of the brood stock showed seasonal fluctuations in reproduction under constant laboratory conditions. The recommended temperature range and test conditions have to be further investigated.

Molecular Evolution under Fitness Fluctuations

Molecular evolution is a stochastic process governed by fitness, mutations, and reproductive fluctuations in a population. Here, we study evolution where fitness itself is stochastic, with random switches in the direction of selection at individual genomic loci. As the correlation time of these fluctuations becomes larger than the diffusion time of mutations within the population, fitness changes from an annealed to a quenched random variable. We show that the rate of evolution has its maximum in the crossover regime, where both time scales are comparable. Adaptive evolution emerges in the quenched fitness regime (evidence for such fitness fluctuations has recently been found in genomic data). The joint statistical theory of reproductive and fitness fluctuations establishes a conceptual connection between evolutionary genetics and statistical physics of disordered systems.

Clustering of diffusing organisms.

Recently, a "Brownian bugs" model has been proposed as a possible explanation for the clustering of organisms such as planktons [W.R. Young, A.J. Roberts, and G. Stuhne, Nature (London) 412, 328 (2001)]. In this model, diffusing organisms die and give birth with equal probabilities and are independent of each other. The clustering phenomenon is due to the discreteness of birth and death events and cannot be explained in the framework of the continuous model of population dynamics. We show by exact calculation that at dimensions smaller than or equal to 2, this simple mechanism is enough to provoke aggregations of the organisms. At dimensions higher than 2, the clustering phenomenon disappears, but reproductive fluctuations can still be large compared to diffusive ones.

The Influences of Conspecific and Heterospecific Residents on Colonization.

To determine if dispersing prairie voles, Microtus ochrogaster, are prevented from establishing home ranges in habitat already occupied by conspecifics or potentially competitive species, voles were introduced into enclosed populations of: the same species; southern bog lemmings, Synaptomys cooperi; cotton rats, Sigmodon hispidus; or an empty enclosure. The results indicated that colonization by dispersing voles was negatively affected by resident conspecifics. Introduced females were more strongly affected than males during the vegetative growing season but not during the nongrowing season when reproductive activity is typically low. Resident bog lemmings also negatively affected colonization by dispersing voles. However, both sexes of introduced voles were similarly affected in both seasons. There was no evidence of postcolonization competitive effects, suggesting that interspecific competition does not occur between established resident individuals. Cotton rats, which have only recently become part of the small mammal community in Kansas, did not adversely affect colonization by dispersing voles or have adverse post-colonization effects on their survival and reproduction. The ability of residents to inhibit colonization by another species may facilitate the coexistence of M. ochrogaster and Synaptomys cooperi by retarding the competitive exclusion of either species until annual fluctuations in reproduction and density create an abundance of suitable but unoccupied space. This type of coexistence is similar to the storage effect in lottery models of competitive coexistence.