Sub-antarctic House mice: colonization, survival and selection

House mice have colonized and survived successfully on a number of Sub-Antarctic islands, where the mean annual temperature is only about 5°C, but where there is little seasonal fluctuation in climate. Surprisingly this allows almost continuous breeding. On at least two islands (Macquarie and Marion), there are significant changes in gene frequency in electro-phoretically detected enzymes between young (less than three months of age) and old animals from the same population. This indicates natural selection acting in opposite directions at different stages of the life cycle. However the genetical compositions of the Macquarie and Marion populations are more distinct from each other than either is from most British samples. This means that detailed studies of the Sub-Antarctic mouse populations are likely to reveal much about local adaptation, while comparison between the responses of different populations may lead to important generalisations about the possible reaction to evolutionary challenges of a species living close to its physiological limit.     

The population ecology of house mice (Mus domesticus) on the Isle of May, Scotland

The colonizing ability, catholic habitat utilization and wide distribution of house mice ( Mus domesticus , Rutty) are indicators of their ecological resilience. Numerous studies have been made of commensal, caged and free-living mouse populations though few have assessed the relative importance of physiological and genetical components of adaptability in a simple ecosystem. This paper reports such findings, derived from live-trapping which formed part of an inter-disciplinary study of adaptability in a feral population of house mice living on a small Scottish island (57 ha).
The population size ranged from450–3250 animals. A high proportion of mice showed homerange tenacity, though15–20% shifted their range during winter. This 'churning' of the population is consistent with the island population forming an effectively panmictic unit rather than fragmented demes. The breeding season, survival of individuals and change in population size related to patterns of gross climatic variation (temperature and rainfall) so that rates of reproduction and survival were lowest in cold, wet conditions. Thermoregulatory adjustment of the mice to lowered ambient temperatures and its contribution to overwinter survival are discussed. Genetical monomorphism of May Island mice is discussed in relation to their biological performance compared with other populations, especially that of the ecologically comparable Skokholm Island (Wales).     

Ecological genetics of an island population of the House mouse (Mus musculus)

The House mouse ( Mus musculus L.) population on the small Welsh island of Skokholm was founded in the 1890s when a few animals were inadvertently introduced. It has thrived ever since. The animals breed from late March to early October, during which time the population increases 8–10 fold. Winter survival is related to temperature: the spring population can be as low as 100 individuals after a cold winter; if the winter is warm, so many animals survive that high numbers may occur in the following autumn. There are no resident predators of the mice, and no other small mammals on the island.
The population was sampled on 20 occasions between 1957 and 1972, and genetical changes measured by the incidences of non-metrical skeletal variants (which describe a substantial proportion of the genome) and (from 1968–72) by allele and genotype frequencies of electrophoretically detected genes. Two sorts of changes occurred: an irregular but increasing deviation from the genetical composition of the population at the beginning of the study period, and an annual cycle with frequencies changing in one direction during the breeding season and the opposite direction in the winter. Samples collected in the autumn were more similar to each other than spring caught samples, which conforms with independent evidence about the differing environmental contributors to death in different winters, as compared with general homogeneity of mortality factors during the summers. It is concluded that the genetical composition of the population is largely dependent on natural selection, although the agents and intensity of selection change with both seasons and years.     

The natural regulation of buffalo populations in East Africa: II. Reproduction,recruitment and growth*

Aspects of the seasonality of breeding, age-specific fertility, and growth were studied in a sample of animals collected from the Serengeti buffalo population, and compared with two populations in Uganda. Fluctuations in fertility and recruitment were studied by the use of regular aerial photographic samples of herds in the Serengeti. The fluctuations in fertility rate were not related to density and hence could not have regulated the population. Buffalo show a pronounced seasonality in births which is correlated with the quality of ingested food and with rainfall. Since the female has a considerably higher food requirement during late pregnancy and lactation, nutrition is probably an important factor determining this seasonality. Conception does not appear to be influenced by nutrition, for the quality of food remains high throughout the rainy season prior to and during the period of conception. Growth rate, age of first ovulation, and age of sexual maturity do not appear to differ between the Serengeti and Uganda populations. Although there is little difference in fertility between these populations, as measured from the collected samples, little weight can be placed on this evidence, for large fluctuations in fertility can take place from year to year within a population. The fluctuations in the Serengeti population do not appear to be correlated with rainfall, and it is possible that they are random. Fluctuations in recruitment from year to year are also observed. Two sample areas over 100 km apart but within the same population show parallel fluctuations suggesting a similar external influence on the size of the recruitment. This recruitment is not correlated with population size but it may be related to rainfall. Underweight calves at birth have been recorded and this may have been caused by the undernutrition of pregnant females during the dry season through a combination of poor food supply and the demands of the previous lactation.     

Home range behaviour of the monogamous Australian seahorse, <Emphasis Type="Italic">Hippocampus whitei</Emphasis>

We provide a quantitative account of local movements in the monogamous Australian species Hippocampus whitei, as a rare report of home range size in fishes living in seagrass habitats. Our study took place in shallow Posidonia seagrass beds in Port Jackson (Sydney Harbour), principally during January to March. Daily monitoring of individual seahorses during underwater observations revealed that both sexes maintained small and apparently undefended home ranges for several breeding cycles at least. Female home ranges were significantly larger than males, when analysed by both the minimum convex polygon and grid cell methods. Home range size was not correlated with either body size or seahorse density. Presumably, home ranges were small in H. whitei because camouflage (to avoid predation and to capture prey), mate fidelity and parental brooding meant they accrued little benefit (and potentially considerable cost) from moving more extensively. Sex differences in home range size may arise from constraints associated with male pregnancy. These fish are among the most sedentary of vertebrates, with relatively small home ranges equalled only by coral reef species. In terms of their conservation, relatively small protected areas may be sufficient to support breeding populations of H. whitei although that limited movement may result in considerable delays in the recolonisation of depleted areas.     

Low and annually variable migratory connectivity in a long‐distance migrant: Whinchats Saxicola rubetra may show a bet‐hedging strategy

The spatial scale of non‐breeding areas used by long‐distance migrant animals can vary from specific, relatively small non‐breeding areas for each independent breeding population (high connectivity) to a distribution over a large non‐breeding area with mixing of breeding populations (low connectivity). Measuring variation in the degree of connectivity and how it arises is crucial to predict how migratory animals can respond to global habitat and climate change because low connectivity is likely to be an adaptation to environmental uncertainty. Here, we assess whether use of non‐breeding areas in a long‐distance migrant may be stochastic by measuring the degree of connectivity, and whether it is annually variable. Twenty‐nine wintering Whinchats tagged with geolocators over 2 years within 40 km² in central Nigeria were found to be breeding over 2.55 million km² (26% of the land area of Europe), without an asymptote being approached in the relationship between area and sample size. Ranges differed in size between years by 1.51 million km² and only 15% of the total breeding range across both years overlapped (8% overlap between years when only first‐year birds were considered), well above the range size difference and below the proportion of overlap that would be predicted from two equivalent groups breeding at random locations within the observed range. Mean distance between breeding locations (i.e. migratory spread) differed significantly between years (604 ± 18 km in 2013 and 869 ± 33 km in 2014). The results showed very low and variable connectivity that was reasonably robust to the errors and assumptions inherent in the use of geolocators, but with the caveat of having only ranges of 2 years to compare, and the sensitivity of range to the breeding locations of a small number of individuals. However, if representative, the results suggest the scope for between‐year variation (cohort effects) to determine migrant distribution on a large scale. Furthermore, for species with similarly low connectivity, we would predict breeding population trends to reflect average conditions across large non‐breeding areas: thus, as large areas of Africa become subject to habitat loss, migrant populations throughout Europe will decline.     

A general model of site-dependent population regulation: population-level regulation without individual-level interactions

In this paper, we use a modeling approach to explore the population regulatory consequences of individual choices for where to breed in heterogeneous environments. In contrast to standard models, we focus on individuals that interact only indirectly through their choices of breeding sites (i.e., individuals preempt the occupation of a breeding site by others when they choose to breed there). We consider the consequences of individuals choosing breeding sites either randomly or sequentially from best to worst. Our analysis shows that average per-capita fecundity of the population is independent of the number of occupied breeding sites if individuals choose sites at random and that variation in average per-capita fecundity increases as population size declines. In contrast, if individuals choose breeding sites sequentially from highest to lowest quality, then as population size increases average per-capita fecundity declines and variation in average per-capita fecundity increases. Consequently, aggregate population-level demographic rates can change in ways that generate population regulation, even when change in population size does not change the demographic performance of any individual on any particular breeding site. However, such regulation occurs only when individuals make adaptive choices of where to breed. Because variation in average per-capita fecundity decreases when population size declines, populations regulated in a site-dependent manner should be much less susceptible to the vicissitudes of small population size than those which choose breeding sites at random.     

Population and individual elephant response to a catastrophic fire in Pilanesberg National Park

In predator-free large herbivore populations, where density-dependent feedbacks occur at the limit where forage resources can no longer support the population, environmental catastrophes may play a significant role in population regulation. The potential role of fire as a stochastic mass-mortality event limiting these populations is poorly understood, so too the behavioural and physiological responses of the affected animals to this type of large disturbance event. During September 2005, a wildfire resulted in mortality of 29 (18% population mortality) and injury to 18, African elephants in Pilanesberg National Park, South Africa. We examined movement and herd association patterns of six GPS-collared breeding herds, and evaluated population physiological response through faecal glucocorticoid metabolite (stress) levels. We investigated population size, structure and projected growth rates using a simulation model. After an initial flight response post-fire, severely injured breeding herds reduced daily displacement with increased daily variability, reduced home range size, spent more time in non-tourist areas and associated less with other herds. Uninjured, or less severely injured, breeding herds also shifted into non-tourist areas post-fire, but in contrast, increased displacement rate (both mean and variability), did not adjust home range size and formed larger herds post-fire. Adult cow stress hormone levels increased significantly post-fire, whereas juvenile and adult bull stress levels did not change significantly. Most mortality occurred to the juvenile age class causing a change in post-fire population age structure. Projected population growth rate remained unchanged at 6.5% p.a., and at current fecundity levels, the population would reach its previous level three to four years post-fire. The natural mortality patterns seen in elephant populations during stochastic events, such as droughts, follows that of the classic mortality pattern seen in predator-free large ungulate populations, i.e. mainly involving juveniles. Fire therefore functions in a similar manner to other environmental catastrophes and may be a natural mechanism contributing to population limitation. Welfare concerns of arson fires, burning during "hot-fire" conditions and the conservation implications of fire suppression (i.e. removal of a potential contributing factor to natural population regulation) should be integrated into fire management strategies for conservation areas.     

Effective Sizes for Subdivided Populations

Many derivations of effective population sizes have been suggested in the literature; however, few account for the breeding structure and none can readily be expanded to subdivided populations. Breeding structures influence gene correlations through their effects on the number of breeding individuals of each sex, the mean number of progeny per female, and the variance in the number of progeny produced by males and females. Additionally, hierarchical structuring in a population is determined by the number of breeding groups and the migration rates of males and females among such groups. This study derives analytical solutions for effective sizes that can be applied to subdivided populations. Parameters that encapsulate breeding structure and subdivision are utilized to derive the traditional inbreeding and variance effective sizes. Also, it is shown that effective sizes can be determined for any hierarchical level of population structure for which gene correlations can accrue. Derivations of effective sizes for the accumulation of gene correlations within breeding groups (coancestral effective size) and among breeding groups (intergroup effective size) are given. The results converge to traditional, single population measures when similar assumptions are applied. In particular, inbreeding and intergroup effective sizes are shown to be special cases of the coancestral effective size, and intergroup and variance effective sizes will be equal if the population census remains constant. Instantaneous solutions for effective sizes, at any time after gene correlation begins to accrue, are given in terms of traditional F statistics or transition equations. All effective sizes are shown to converge upon a common asymptotic value when breeding tactics and migration rates are constant. The asymptotic effective size can be expressed in terms of the fixation indices and the number of breeding groups; however, the rate of approach to the asymptote is dependent upon dispersal rates. For accurate assessment of effective sizes, initial, instantaneous or asymptotic, the expressions must be applied at the lowest levels at which migration among breeding groups is nonrandom. Thus, the expressions may be applicable to lineages within socially structured populations, fragmented populations (if random exchange of genes prevails within each population), or combinations of intra- and interpopulation discontinuities of gene flow. Failure to recognize internal structures of populations may lead to considerable overestimates of inbreeding effective size, while usually underestimating variance effective size.     

The measurement of villus cell population size in the mouse small intestine in normal and abnormal states: a comparison of absolute measurements with morphometric estimators in sectioned immersion-fixed material

Abstract From a functional viewpoint, the most important part of the small intestinal mucosa is the villus epithelium; in the experimental study of intestinal adaptation it is often necessary to estimate the size of the population. For these reasons, a systematic study of methods of measuring the size of the villus cell population was undertaken in villi of normal morphology from control animals, and in villi of abnormal morphology as produced by treatment of mice with cytosine arabinoside (Ara-C).
The villus cell population can be measured with precision and accuracy in both normal and abnormal mucosal states, with a relative standard error usually less than 5%, with good reproducibility, and with very low counting errors. In the mouse a practically linear relationship between the villus cell population size and position in the small intestine can be shown. In normal, control animals, linear estimates of villus population, for example the villus height, the villus core height, and the villus row count measured in sections of immersion-fixed material, were found to be rough approximations as indicators of the villus cell population, and were highly correlated with it. Product variables, comprising the products of a height with a width measurement, show a large improvement over the linear variables as estimators of villus cell population. In populations of abnormally shaped villi produced by Ara-C, both linear and product variables showed a considerable decrease in correlation with the villus cell population. Consequently, indirect, linear measurements of the villus population size do not accurately reflect the size of the villus population in abnormal villi.
Finally, a method comparing theoretical and measured surface: volume indices was used to indicate that the most appropriate shape for normal mouse villi is a simple cylinder; this method would also be applicable for other villus cell populations.     

The measurement of villus cell population size in the mouse small intestine in normal and abnormal states: a comparison of absolute measurements with morphometric estimators in sectioned immersion-fixed material

From a functional viewpoint, the most important part of the small intestinal mucosa is the villus epithelium; in the experimental study of intestinal adaptation it is often necessary to estimate the size of the population. For these reasons, a systematic study of methods of measuring the size of the villus cell population was undertaken in villi of normal morphology from control animals, and in villi of abnormal morphology as produced by treatment of mice with cytosine arabinoside (Ara-C). The villus cell population can be measured with precision and accuracy in both normal and abnormal mucosal states, with a relative standard error usually less than 5%, with good reproducibility, and with very low counting errors. In the mouse a practically linear relationship between the villus cell population size and position in the small intestine can be shown. In normal, control animals, linear estimates of villus population, for example the villus height, the villus core height, and the villus row count measured in sections of immersion-fixed material, were found to be rough approximations as indicators of the villus cell population, and were highly correlated with it. Product variables, comprising the products of a height with a width measurement, show a large improvement over the linear variables as estimators of villus cell population. In populations of abnormally shaped villi produced by Ara-C, both linear and product variables showed a considerable decrease in correlation with the villus cell population. Consequently, indirect, linear measurements of the villus population size do not accurately reflect the size of the villus population in abnormal villi. Finally, a method comparing theoretical and measured surface: volume indices was used to indicate that the most appropriate shape for normal mouse villi is a simple cylinder; this method would also be applicable for other villus cell populations.     

An under-appreciated difficulty: sampling of plant populations for analysis using molecular markers

Results of studies using molecular markers for determining demographic and genetical population parameters especially in plants or sessile animals under field conditions are strongly dependent on the sampling strategy adopted. There are two critical decisions to make when determining this strategy: (i) what is the unit to be sampled?, (ii) how should units to be sampled in the field be selected? For the first decision, there are two conceptually different approaches: sampling ramets of clonal plants as units (to get information about within-genet parameters, such as genet sizes or numbers) and sampling genets of clonal or non-clonal plants as units (to get information of the genetic structure of the population). For the second decision, it is critically important to make the goal of the study explicit. We argue that in this case fully random sampling is needed only when an estimate of the true value of the population parameter is needed; if a comparison between populations is the goal, however, other sampling schemes may be adopted. The efficiency of different types of sampling strategies to recover relative values in a spatially extended population is studied by means of a spatially explicit simulation model. The results show that a regular pattern of sampling is best for obtaining information on genet sizes or inbreeding coefficients; in contrast, random or hierarchical sampling strategies are better for obtaining information on parameters that are based on comparison of pairs of individuals, such as distribution of genet sizes or autocorrelation in genetic structure. A set of recommendations is provided for designing a good sampling strategy.     

Area-dependent migration by ringlet butterflies generates a mixture of patchy population and metapopulation attributes

Interpretation of spatially structured population systems is critically dependent on levels of migration between habitat patches. If there is considerable movement, with each individual visiting several patches, there is one ”patchy population”; if there is intermediate movement, with most individuals staying within their natal patch, there is a metapopulation; and if (virtually) no movement occurs, then the populations are separate (Harrison 1991, 1994). These population types actually represent points along a continuum of much to no mobility in relation to patch structure. Therefore, interpretation of the effects of spatial structure on the dynamics of a population system must be accompanied by information on mobility. We use empirical data on movements by ringlet butterflies, Aphantopus hyperantus, to investigate two key issues that need to be resolved in spatially-structured population systems. First, do local habitat patches contain largely independent local populations (the unit of a metapopulation), or merely aggregations of adult butterflies (as in patchy populations)? Second, what are the effects of patch area on migration in and out of the patches, since patch area varies considerably within most real population systems, and because human landscape modification usually results in changes in habitat patch sizes? Mark-release-recapture (MRR) data from two spatially structured study systems showed that 63% and 79% of recaptures remained in the same patch, and thus it seems reasonable to call both systems metapopulations, with some capacity for separate local dynamics to take place in different local patches. Per capita immigration and emigration rates declined with increasing patch area, while the resident fraction increased. Actual numbers of emigrants either stayed the same or increased with area. The effect of patch area on movement of individuals in the system are exactly what we would have expected if A. hyperantus were responding to habitat geometry. Large patches acted as local populations (metapopulation units) and small patches simply as locations with aggregations (units of patchy populations), all within 0.5 km². Perhaps not unusually, our study system appears to contain a mixture of metapopulation and patchy-population attributes.     

Predicting the annual effective size of livestock populations

Effective population size (Ne) is an important parameter determining the genetic structure of small populations. In natural populations, the number of adults (N) is usually known and Ne can be estimated on the basis of an assumed ratio Ne/N, usually found to be close to 0.5. In farm animal populations, apart from using pedigrees or genetic marker information, Ne can be estimated from the number N of breeding animals, and a value of 1 is commonly assumed for the ratio Ne/N. The purpose of this paper is to show the relation between effective population size and breeding herd size in livestock species. With overlapping generations, Ne can be predicted knowing the number of individuals entering the population per generation and the variance of family size, the latter being directly related to the survival pattern (or replacement policy) in the breeding herd. Assuming an ideal survivorship leading to a geometric age distribution, it can be shown that the number of breeding animals tends to overestimate effective size, particularly in early-maturing species. The ratio of annual effective size to the number of breeding animals is shown to be equal to [1 + (a- 1)(1 - s)]2/(1 - s2), where a is the age at first offspring and s is the survival rate (including culling) of the parents between successive births. This expression shows to what extent inbreeding may be determined by demography or culling policy independently of the actual herd size. In many situations a fast replacement or an early culling will increase annual effective size. Consequences for the management of small populations are discussed.     

Effects of selective harvest on antler size in white-tailed deer: A modeling approach

Selective harvesting in wild deer (Odocoileus spp.) populations is a common practice that may influence antler size. However, in free-ranging populations, response due to selection is unknown or difficult to quantify because antlers are influenced by nutrition and population demographics. We used quantitative genetic models to predict how white-tailed deer (O. virginianus) antlers would respond to selection and what variables (i.e., population size, age structure, mating ratio, and heritability) most affected antler size. We validated our quantitative genetics program by comparing model results with a population of deer used for controlled breeding experiments; modeled antler points (AP) and score increased (2.2–4.3 AP and 48.5–97.7 cm, respectively) after 8 years of selection, similar to observed increases in AP (3.2) and score (92.3 cm) from the controlled population. In modeled free-ranging populations, mating ratio, age structure, and heritability were more important in influencing antler size than size of the population. However, response to selection in free-ranging populations was lower (0.1–0.9 AP) than controlled breeding populations even after 20 years of selection. These results show that selective harvesting of free-ranging white-tailed deer may be inefficient to change population-level genetic characteristics related to antler size. Response of antlers in free-ranging deer will be less than controlled populations, and possibly modeled free-ranging simulations, because individual reproductive success of males is lower, breeding is done by a large group of males, and reproductive and survival rates are lower. These factors, and others, reduce the amount of improvement that can be made to antlers due to selection. Therefore, selective harvesting in free-ranging populations should be justified for managing population demographics and dynamics, but not for changing the genetic characteristics of populations. © 2011 The Wildlife Society.     

Analysis of genetic diversity in red clover (Trifolium pratense L.) breeding populations as revealed by RAPD genetic markers.

Red clover is an important forage legume species for temperate regions and very little is known about the genetic organization of its breeding populations. We used random amplified polymorphic DNA (RAPD) genetic markers to address the genetic diversity and the distribution of variation in 20 breeding populations and cultivars from Chile, Argentina, Uruguay, and Switzerland. Genetic distances were calculated for all possible pairwise combinations. A high level of polymorphism was found and the proportion of polymorphic loci across populations was 74.2%. A population derived from a non-certified seedlot displayed a higher proportion of polymorphic loci than its respective certified seedlot. Gene diversity values and population genetics parameters suggest that the populations analyzed are diverse. An analysis of molecular variance (AMOVA) revealed that the largest proportion of variation (80.4%) resides at the within population level. RAPD markers are a useful tool for red clover breeding programs. A dendrogram based on genetic distances divided the breeding populations analyzed into three distinct groups. The amount and partition of diversity observed can be of value in identifying the populations that parents of synthetic cultivars are derived from and to exploit the variation available in the populations analyzed.     

Integrating batch marks and radio tags to estimate the size of a closed population with a movement model

Movement models require individually identifiable marks to estimate the movement rates among strata. But they are relatively expensive to apply and monitor. Batch marks can be readily applied, but individual animal movements cannot be identified. We describe a method to estimate population size in a stratified population when movement takes place among strata and animals are marked with a combination of batch and individually identifiable tags. A hierarchical model with Bayesian inference is developed that pools information across segments on the detection efficiency based on radio‐tagged fish and also uses the movement of the radio‐tagged fish to impute the movement of the batch‐marked fish to provide estimates of the population size on a segment and river level. The batch marks provide important information to help estimate the movement rates, but contribute little to the overall estimate of the population size. In this case, the approximate equal catchability among strata in either sample obviates the need for stratification.     

Slow response to strong disturbance in an insect population with a temporal refuge

The extent to which perturbations are modulated and delayed in population systems is a question of considerable theoretical and practical interest. Organisms with a temporal refuge, for example insects with prolonged diapause, are likely to have strongly buffered populations with long response lags, but little is known concerning how disturbances are actually mediated in natural populations. We show experimentally that the gall midge Contarinia vincetoxici has a prolonged diapause with a "bank" in the soil where diapausing larvae can reside for at least six winters. This bank acts as a strong buffer against disturbance. We stopped recruitment to the larval bank during eight years by removing all new galls, but no significant effects on gall density were found. Response lags may thus be very long even in populations of apparently shortlived animals. Population fluctuations during the last decade were evidently largely determined by events taking place prior to this period.     

Fine-scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations

We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km(2). Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations < or = 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation.     

Population ecology of Mus musculus on Mana Island, New Zealand

Feral house mice ( Mus musculus ) living on 217 ha Mana Island, New Zealand, with no mammalian predators, were snap-trapped and autopsied. A 7-month breeding season took the population from a spring low to extremely high density in autumn. Litters were largest in the middle of the breeding season, and significantly larger on Mana than on the New Zealand mainland. Litter size in early pregnancy was similar for young and old mice but more embryos were resorbed by old females. The breeding season ended in April when adult females stopped ovulating and young failed to mature. When the population declined over winter no animals bred, they all lost weight, and even previously mature males lost their reproductive ability. Mice continue to grow throughout life and become larger than mice in most populations on the New Zealand mainland. The regular and pronounced seasonal pulse in Mana's mouse population contrasts with longer-term fluctuations generally seen in mainland populations at lower density in indigenous forest. These differences may be explained by absence of predators, habitat features or lack of any chance to disperse on the island.