Assessing seasonal demographic covariation to understand environmental‐change impacts on a hibernating mammal

Natural populations are exposed to seasonal variation in environmental factors that simultaneously affect several demographic rates (survival, development and reproduction). The resulting covariation in these rates determines population dynamics, but accounting for its numerous biotic and abiotic drivers is a significant challenge. Here, we use a factor‐analytic approach to capture partially unobserved drivers of seasonal population dynamics. We use 40 years of individual‐based demography from yellow‐bellied marmots (Marmota flaviventer ) to fit and project population models that account for seasonal demographic covariation using a latent variable. We show that this latent variable, by producing positive covariation among winter demographic rates, depicts a measure of environmental quality. Simultaneously, negative responses of winter survival and reproductive‐status change to declining environmental quality result in a higher risk of population quasi‐extinction, regardless of summer demography where recruitment takes place. We demonstrate how complex environmental processes can be summarized to understand population persistence in seasonal environments

Evolutionary Entropy: A Predictor of Body Size, Metabolic Rate and Maximal Life Span

Body size of organisms spans 24 orders of magnitude, and metabolic rate and life span present comparable differences across species. This article shows that this variation can be explained in terms of evolutionary entropy, a statistical parameter which characterizes the robustness of a population, and describes the uncertainty in the age of the mother of a randomly chosen newborn. We show that entropy also has a macroscopic description: It is linearly related to the logarithm of the variables body size, metabolic rate, and life span. Furthermore, entropy characterizes Darwinian fitness, the efficiency with which a population acquires and converts resources into viable offspring. Accordingly, entropy predicts the outcome of natural selection in populations subject to different classes of ecological constraints. This predictive property, when integrated with the macroscopic representation of entropy, is the basis for enormous differences in morphometric and life-history parameters across species

Dynamics of leprosy in Nine-Banded Armadillos: Net reproductive number and effects on host population dynamics

Leprosy (or Hansen’s disease) remains an important public health challenge globally, with an estimated 5.5 million total number of cases and 200,000–300,000 new cases reported annually. The nine-banded armadillo (Dasypus novemcinctus) is the only known natural non-human vertebrate host of Mycobacterium leprae, the causative agent of leprosy, in the Americas, yet gaps in knowledge remain regarding the dynamics of leprosy in wild populations. Here, we used data from a six-year study of a population of armadillos in Mississippi, USA to quantify the influence of leprosy on armadillo population dynamics, and to investigate leprosy dynamics within the host population. Leprosy reduced annual survival of adult armadillos by ∼15%, and growth rate of the population by ∼13%. The annual infection rate for adult armadillos (i.e., probability that a non-leprous adult armadillo seroconverts, conditional on survival) was 0.18, with no possibility of recovery. Assuming frequency-dependent transmission of leprosy, 18% to 25% of the adult armadillos will acquire leprosy infection in the long run. Finally, the basic reproductive ratio (R0) was 1.36, suggesting 36% increase in seroprevalence per leprosy generation. Assuming that leprosy generation time is 3–5 years, M. leprae will spread within the armadillo population at the rate of 7–12% per year. Our results are consistent with recent evidence that leprosy infection in armadillos in the USA is spreading rapidly with a concomitant increase in risk for zoonotic transmissions

Analysis of interspecific competition in perennial plants using life table response experiments

The impact of interspecific competition is usually measured by its effect upon plant growth, neglecting impacts upon other stages of the life cycle such as fecundity which have a direct influence upon individual fitness and the asymptotic population growth rate of a population (lambda). We used parameterized matrix models for three perennial plant species grown with and without interspecific competition to illustrate how the methodology of Life Table Response Experiments (LTRE) can be used to link any change in population dynamics to changes in any part of the life cycle. Plants were herbaceous grassland species grown for two years in a field experiment at Rothamsted Experimental Station, England. Interspecific competition reduced X by over 90% in all species. Survival and growth were slightly affected by competition whereas plant fecundity was greatly reduced. Nearly all of the observed difference in X between the competition treatments was explained by the fecundity terms, and more precisely by a large difference in the number of seeds, and a high sensitivity of X to the germination rate. Whereas most competition studies focus on the measurement of change in individual fitness, our study illustrates how informative it is to take account not only of the effect of competition upon vital rates but also of how different vital rates affect population growth rate

Applying search theory to determine the feasibility of eradicating an invasive population in natural environments

The detectability of invasive organisms influences the feasibility of eradicating an infestation. Search theory offers a framework for defining and measuring detectability, taking account of searcher ability, biological factors and the search environment. In this paper, search theory concepts are incorporated into a population model, and the costs of search and control are calculated as functions of the amount of search effort (the decision variable). Simulations are performed on a set of weed scenarios in a natural environment, involving different combinations of plant longevity, seed longevity and plant fecundity. Results provide preliminary estimates of the cost and duration of eradication programs to assist in prioritising weeds for control. The analysis shows that the success of an eradication program depends critically on the detectability of the target plant, the effectiveness of the control method, the labour requirements for search and control, and the germination rate of the plant. Copyright 2007 The Authors Journal compilation 2007 Australian Agricultural and Resource Economics Society Inc. .

Age at maturity in cavies and guinea-pigs (Cavia aperea and Cavia aperea f. porcellus): influence of social factors

Trillmich F, Laurien-Kehnen C, Adrian A, Linke S. Age at maturity in cavies and guinea-pigs (Cavia aperea and Cavia aperea f. porcellus): influence of social factors. JOURNAL OF ZOOLOGY. 2006;268(3):285-294.Age at maturity, a particularly important parameter in the life history of small mammals, contributes greatly to fitness. Social influences on age at maturity have been demonstrated for altricial rodents, in particular, mice. Nothing is known about such effects in precocial small mammals. Wild cavies Cavia aperea are born in a highly precocial state and mature early in life, briefly after weaning. We investigated whether the wild cavy C. aperea and the domestic guinea-pig Cavia aperea f. porcellus reach maturity earlier in the presence of adults of the opposite sex. Juvenile females kept in pairs without males showed first vaginal opening (=oestrus) when 59 days old in cavies and at about 40 days in the guinea-pig. However, in the company of adult males, cavy females kept in pairs reached maturity when about 30 days old, and guinea-pig females when 26 days old. Most cavy females experienced successful pregnancy following first vaginal opening. In cavies, female mass at birth and at first oestrus was not correlated with age at first oestrus. In guinea-pigs, birth mass predicted age at maturity only when a male was present. The growth rate from birth to first oestrus related to age at first oestrus. In the wild cavy, the presence of a male appeared to influence maturation more between days 25 and 30 than earlier in life. Male C. aperea matured and had fully descended testes when about 65-70 days old. All male cavies produced abundant motile sperm from day 75. First successful copulations occurred at about the same age. Surprisingly, the priming effect of the presence of an adult male on female maturation proved stronger in these highly precocial caviomorphs than in altricial rodents investigated so far

Demography of fluctuating populations: temporal and phase-related changes in vital rates of Microtus ochrogaster

1. Small mammal population fluctuations, cyclic or not, have been an ecological puzzle and a source of heated debate among ecologists. Identifying the demographic parameters that covary closely with density changes can help elucidate the underlying causes of population fluctuations, but few studies have reported rigorous estimates of these parameters. 2. We applied capture-mark-recapture analysis to twice-weekly trapping data from a long-term study of a fluctuating Microtus ochrogaster (prairie vole) population in Illinois, USA to estimate stage-specific apparent survival and maturation rates. We also estimated population density, fecundity rate, age at maturity and life span on a weekly basis. 3. Survival, maturation and fecundity rates exhibited phase-related changes during major density fluctuations, but they showed density-independent temporal variations during the prolonged low-density phases. Among these variables, maturation and juvenile survival rates covaried most closely with population density. 4. These results suggest that phase-related changes in maturation and juvenile survival rates are likely to be the main demographic factors driving the dynamics of our study population. 5. Phase-related changes in maturation rates provide a plausible demographic explanation of density fluctuations in our study population. Our results suggest that direct predation may not be necessary for large-scale fluctuations in M. ochrogaster abundance