Long-term Population Viability Research Articles

Evolutionary effects of alternative artificial propagation programs: implications for viability of endangered anadromous salmonids.

Most hatchery programs for anadromous salmonids have been initiated to increase the numbers of fish for harvest, to mitigate for habitat losses, or to increase abundance in populations at low abundance. However, the manner in which these programs are implemented can have significant impacts on the evolutionary trajectory and long-term viability of populations. In this paper, we review the potential benefits and risks of hatchery programs relative to the conservation of species listed under the US Endangered Species Act. To illustrate, we present the range of potential effects within a population as well as among populations of Chinook salmon (Oncorhynchus tshawytscha) where changes to major hatchery programs are being considered. We apply evolutionary considerations emerging from these examples to suggest broader principles for hatchery uses that are consistent with conservation goals. We conclude that because of the evolutionary risks posed by artificial propagation programs, they should not be viewed as a substitute for addressing other limiting factors that prevent achieving viability. At the population level, artificial propagation programs that are implemented as a short-term approach to avoid imminent extinction are more likely to achieve long-term population viability than approaches that rely on long-term supplementation. In addition, artificial propagation programs can have out-of-population impacts that should be considered in conservation planning.

A conceptual model of ecological connectivity in the Shellharbour Local Government Area, New South Wales, Australia

The conservation of biological diversity in landscapes dominated by human use is emerging as an increasingly significant challenge, given the rate at which the Earth's remaining vegetation resources are being lost. Whilst traditional approaches to conservation have relied upon the ability of species to persist within the scattered fragments to which they have been confined, recent scientific evidence suggests that the long-term viability of fragmented populations may only be secured through the establishment of ecological connectivity between existing fragments. In the absence of a suitable methodology within which to design connective habitat configurations, a conceptual approach to landscape design was devised for a highly urbanised environment within the Shellharbour Local Government Area (LGA), New South Wales (NSW). This approach utilises beneficial landscape attributes advocated in the literature, and tailors existing rapid assessment methodologies traditionally used to provide simple measures of ecosystem health. Using this methodology, conservationally significant stepping-stone sites were identified between selected terminal habitat patches. The determination of an optimal corridor configuration linking these patches was found to heavily utilise riparian habitat and adjacent residential yard space. Planting endemic species in these areas will support ecological flow by increasing the area of core habitat relative to edge habitat.

Metapopulation Dynamics of Bobolinks Occupying Agricultural Grasslands in the Midwestern United States

ABSTRACT A metapopulation is any set of populations that are patchily distributed and potentially connected by dispersal. This broad definition includes classical, mainland-island, source-sink, patchy and non-equilibrium metapopulations. To ensure long-term regional population viability in a fragmented landscape we need a better understanding of metapopulation dynamics. To determine which metapopulation model applies to a given species, Stith et al. (1996) developed a classification scheme using species-specific estimates of dispersal distance and local extinction risk. We used this scheme to classify bobolink (Dolichonyx oryzivorus) populations occupying fragmented, agricultural grasslands in the Midwestern United States. We estimated the distribution of dispersal distances using mark-recapture techniques and calculated local extinction risk. Dispersal rate and turnover were high, indicating that populations were highly connected. Local extinction probability was 4%, indicating that populations were “mid...

Integrating population demography, genetics and self-incompatibility in a viability assessment of the Wee Jasper Grevillea (Grevillea iaspicula McGill., Proteaceae)

Grevillea iaspicula is an endangered shrub known from only eight small populations (<250 individuals) in south-eastern Australia. The species is threatened by combined ecological and genetic factors, e.g. land conversion, weed invasion, low recruitment and low gene flow among populations. The populations also show large variance in male fitness and limited mate availability which are thought to arise as a consequence of gametophytic self-incompatibility (GSI). This study has used an individual-based, spatially explicit simulation model to explore the interaction between GSI and mate limitation in this species, as well as its effect on long-term population viability. The model was parameterised with demographic and genetic data obtained from 2 years of population monitoring. Simulation results identified extremely low establishment rates as the most critical factor currently influencing the persistence of G. iaspicula populations and indicated that the extant populations are at serious risk of extinction in the near future unless this is altered by, at very least, an order of magnitude higher. SI was shown to affect the magnitude of variation in establishment but this effect was masked when establishment was critically low. Disassortative mating, owing to low allelic richness at the S-locus, had the negative demographic effect of restricting mating to relatively few compatible plants. Restricted mate availability imposed additional limitations to the viability of populations but, given a 20-fold increase in establishment rate, population fluctuations stabilised. The long-term viability of G. iaspicula is bleak without artificial augmentation of the populations but management planning must also consider genetic processes, including SI, to ensure such strategies optimise the benefits gained.

Human-Caused Mortality and Population Trends of American Marten and Fisher in a U.S. National Park

American marten (Martes americana) and fisher (M. pennanti) are susceptible to overharvest. National Park Service policies require managers to ensure long-term population viability of native wildlife while concurrently provide recreation opportunities, which can include harvest of wildlife. I investigated human-caused mortality factors of American martens and fishers in Pictured Rocks National Lakeshore (PRNL), Michigan, from May-December 2001-2005. Thirty-five martens and 14 fishers were captured and survival was monitored using radio telemetry. Four martens were legally trapped, one marten was killed by a vehicle collision within PRNL, and three martens died of natural causes. The only fisher mortality was through legal trapping within PRNL. In addition, vehicles in the study area killed an uncollared marten and fisher. Greatest marten mortality occurred during the harvest season in December, with only males reportedly harvested. Overall, marten and fisher survival from June-December was 0.803 (95% confidence interval [CI]: 0.689 to 0.882) and 0.812 (95% CI: 0.374 to 0.977), respectively. Using survival rates from this study and reported rates of fecundity, I estimated that current marten mortality rates are sustainable and that the population was increasing at a rate of 16%/year. Survival data and harvest records suggest that the fisher population is stable or increasing. Human-caused mortality appears to be the greatest source of mortality for martens and fishers at PRNL. Although current harvest rates are comparatively low, continued monitoring of harvest within and adjacent to PRNL, in addition to monitoring vehicle collisions, is warranted to ensure viable populations are maintained.

Conservation and the genetics of populations

Conservation and the genetics of populations

Spatial Ecology of Bobcats and Gray Foxes in Urban and Rural Zones of a National Park

Urbanization threatens the persistence of many wildlife populations, particularly those of wide-ranging and low-density species such as mammalian carnivores. Effective conservation of carnivore populations requires an understanding of the impacts of adjacent urbanization on carnivores in reserves. I compared the spatial ecology of bobcats (Lynx rufus) and gray foxes (Urocyon cinereoargenteus) between urban and rural zones of a national park in northern California, USA. In the urban zone, gray foxes used the entire landscape from interior natural areas across the park edges and into the neighboring developed areas, although fox core areas were always within the park. Bobcats never entered development, and radiocollared adult female bobcats maintained home ranges in the interior of the park, far from the urban edge. Bobcats appeared to avoid crossing paved roads, while foxes crossed roads regularly. For adult female bobcats, home ranges were smaller in the urban zone, and core areas were both smaller and overlapped more. Home range size and overlap did not differ between zones for gray foxes. Bobcats seem to be more affected by the proximity of urbanization than foxes, perhaps because of differences in diet and social structure. The more flexible use of the landscape by foxes may give them access to increased resources and habitat, but also may expose them to more human-associated risks. If female bobcats are more sensitive to urbanization, this sensitivity could affect the long-term viability of bobcat populations in urban areas. Knowledge of how bobcats and gray foxes use the landscape in urban areas will allow more effective conservation and improved coexistence with these widespread carnivores by helping to predict where and why conservation or management issues may occur.

The Effect of Road-Based Fatalities on the Viability of a Peri-Urban Swamp Wallaby Population

Roads and traffic have a multitude of impacts on wildlife populations. Wildlife existing within the confines of fragmented reserves are particularly susceptible to fatalities on roads, especially those situated within urban and semirural matrices. The sustainability of many wildlife populations within reserve fragments are tenuous as roads further subdivide reserved areas and increase the frequency of animal–vehicle contact. Although many studies have assessed the quantity and diversity of fatalities from collisions, few studies have examined the long-term viability of wildlife populations living adjacent to roads. We chose to examine the effects of disturbances, including fatalities on roads, on a population of swamp wallabies (Wallabia bicolor) within the Royal National Park on the urban fringe of Sydney, Australia. Despite having an extensive range, researchers suspect that many local populations of this sole member of Wallabia are in decline. We used a combination of population modeling and sensitivity analysis to assess the impact of disturbances on the population. Under current conditions, the forecast of the population was to decline over the next 100 years with the possibility of becoming extinct. We found that female reproduction and breeding were most influential on the population model. Of the range of management options investigated, by far the most rewarding was the reduction of fatalities on roads, as only a 20% decrease in female fatalities on roads has the potential to reverse the current decline and represents the best option for maintaining long-term viability. We suggest that documentation and subsequent management of road impacts, within the context of other threats, is essential to the conservation of similar species in road-affected environments.

Long-term dynamics and population viability in one of the last populations of the endangered Spiranthes spiralis (Orchidaceae) in the Netherlands

During the last decades, most orchid species in much of Western Europe have suffered significant declines and the long-term survival of the remaining populations remains to a large extent uncertain. In particular, populations at range margins may be more prone to extinction than more central populations, as the former tend to be small and isolated, occur in ecologically marginal habitats and have a lower per-capita reproductive rate. In this study, we investigated the long-term dynamics and population viability of a population at the margin of its range of Spiranthes spiralis in the Netherlands. At present, only 2 out of 40 previously known populations persist. Individual plants were monitored for 24 years and their life span, flowering frequency and vegetative growth were determined. Individual plants showed large temporal variation in sexual and vegetative growth among years. The proportion of flowering plants varied from 0 (no plants were flowering) to 100 (all plants were flowering). Vegetative growth, on the other hand, increased when the number of individuals decreased. Dormancy was present, but occurred only in a few individuals. Using a non-structured population viability model, future prospects of this species were assessed. Calculation of extinction probabilities and estimated times to extinction using the diffusion approximation model showed that the species had a relatively high probability (79%) of surviving the next 20 years, whereas the median time to extinction was forty years. However, because 95% confidence intervals of the population growth included 1, we suggest that continued monitoring and additional genetic research are needed to assess the long-term viability of this species.

Experimental habitat fragmentation increases linkage disequilibrium but does not affect genetic diversity or population structure in the Amazonian liverwort Radula flaccida

Habitat fragmentation increases the migration distances among remnant populations, and is predicted to play a significant role in altering both demographic and genetic processes. Nevertheless, few studies have evaluated the genetic consequences of habitat fragmentation in light of information about population dynamics in the same set of organisms. In a 10,000-km(2) experimentally fragmented landscape of rainforest reserves in central Amazonia, we examine patterns of genetic variation (amplified fragment length polymorphisms, AFLPs) in the epiphyllous (e.g. leaf-inhabiting) liverwort Radula flaccida Gott. Previous demographic work indicates that colonization rates in this species are significantly reduced in small forest reserves. We scored 113 polymorphic loci in 86 individuals representing five fragmented and five experimentally unmanipulated populations. Most of the variation (82%) in all populations was harboured at the smallest (400 m(2)) sampling unit. The mean ((+/-) SD) within-population genetic diversity (Nei's), of forest remnants (0.412 +/- 0.2) was indistinguishable from continuous (0.413 +/- 0.2) forests. Similarly, F(ST) was identical among small (1- and 10-ha) and large (> or = 100-ha) reserves (0.19 and 0.18, respectively), but linkage disequilibrium between pairs of loci was significantly elevated in fragmented populations relative to those in continuous forests. These results illustrate that inferences regarding the long-term viability of fragmented populations based on neutral marker data alone must be viewed with caution, and underscore the importance of jointly evaluating information on both genetic structure and demography. Second, multilocus analyses may be more sensitive to the effects of fragmentation in the short term, although the effects of increasing linkage disequilibrium on population viability remain uncertain.

Is catch-and-release recreational angling compatible with no-take marine protected areas?

Marine protected areas (MPAs) have become a common conservation and management tool for reducing exploitation from the commercial and recreational fisheries sectors. However, the recreational fisheries sector has the potential to be compatible with no-take MPAs when catch-and-release angling is practiced because, in theory, no fish are actually harvested. This presumes that the effects of catch-and-release angling and related activities do not cause appreciable declines in fish populations as a result of direct mortality, sub-lethal effects, or indirect effects on fish habitats, or other problems contrary to the goal of a given MPA. Here, we explore the idea that recreational catch-and-release angling may be compatible with some no-take MPAs provided there are no substantive negative ecological consequences. We argue that it is not currently possible to answer definitively the question of whether recreational catch-and-release fisheries can be compatible with no-take MPAs. Mortality rates of released fish vary extensively (between zero and near 100%) and are influenced by a number of factors including environmental conditions, fishing gear, angler behavior, and species-specific characteristics. Nevertheless, research in the field of catch-and-release is beginning to show that certain handling techniques can significantly reduce post-release mortality in fish. With appropriate regulation and angler education, catch-and-release could help enhance conservation and management goals associated with MPAs while maintaining public support and providing alternative tourism-based revenues for displaced fishers. Until sufficient data are available, research should focus on contrasting the fish community characteristics in regions with no fishing and those that permit catch-and-release fishing (i.e., opportunistic observations and controlled manipulations) as well as population-level mathematical modeling to assess the effects of angling on long-term population viability and ecosystem dynamics. Additional efforts should focus on education and outreach that provide anglers and fishing guides with the best available information to reduce catch-and-release mortality, sublethal angling-induced impairments, and broader effects on aquatic environments.

Effects of an agri-environment scheme on wader populations of coastal meadows of southern Sweden

Survey data on breeding wader densities and grazing intensity on coastal meadows on the Baltic island of Öland from 1988, 1998 and 2003 were used to evaluate density and density-changes of four common and widespread wader species, lapwing Vanellus vanellus, redshank Tringa totanus, oystercatcher Haematopus ostralegus and ringed plover Charadrius hiaticula in relation to grazing intensity. Population trends over time and changes in densities in relation to changes in grazing management were evaluated. Both wader densities and the environmental variable grazing intensity demonstrated significant spatial autocorrelation, but all main results were unaffected when accounting for spatial structure in the statistical tests. Breeding densities of investigated species were positively related to grazing intensity and local changes in grazing management affected the local change in wader densities. However, average grazing intensity increased over time whereas wader numbers generally remained constant or declined. Thus, changes in grazing intensity could not explain changes in overall breeding numbers. One explanation for this is probably that grazing mainly affected distribution of birds. Some evidence of a buffer effect was found in the redshank and ringed plover, in which breeding densities declined proportionally more in non-shore than in shore habitat. This was probably due to a redistribution of birds to shore habitat. It is concluded that grazing management is essential for the occurrence of waders, but might not be sufficient to ensure long-term viability of wader populations on coastal meadows.

Counting primates for conservation: primate surveys in Uganda

Primate census techniques have been developed over the past 35-40 years yet there is still some confusion and great variation in the methods used. This precludes comparisons between sites where different techniques have been used. This paper discusses the variations between the methods that seem to be practiced currently and then describes a census of primates in the forests of western Uganda. Primate density and biomass varied greatly between forests as well as within forests and this is probably related to food availability. Chimpanzee (Pan troglodytes) density was strongly correlated with nest encounter rates from reconnaissance walks in the forest. This result can be used to estimate chimpanzee density in forests where it is difficult to survey this species (e.g., due to security reasons). A total of 4,980 chimpanzee was estimated for Uganda which is higher than previously guessed, but still of conservation concern. Only four forests had more than 500 individuals which gives concern for long-term population viability.

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

The theoretical impacts of anthropogenic habitat degradation on genetic resources have been well articulated. Here we use a simulation approach to assess the magnitude of expected genetic change, and review 31 studies of 23 neotropical tree species to assess whether empirical case studies conform to theory. Major differences in the sensitivity of measures to detect the genetic health of degraded populations were obvious. Most studies employing genetic diversity (nine out of 13) found no significant consequences, yet most that assessed progeny inbreeding (six out of eight), reproductive output (seven out of 10) and fitness (all six) highlighted significant impacts. These observations are in line with theory, where inbreeding is observed immediately following impact, but genetic diversity is lost slowly over subsequent generations, which for trees may take decades. Studies also highlight the ecological, not just genetic, consequences of habitat degradation that can cause reduced seed set and progeny fitness. Unexpectedly, two studies examining pollen flow using paternity analysis highlight an extensive network of gene flow at smaller spatial scales (less than 10 km). Gene flow can thus mitigate against loss of genetic diversity and assist in long-term population viability, even in degraded landscapes. Unfortunately, the surveyed studies were too few and heterogeneous to examine concepts of population size thresholds and genetic resilience in relation to life history. Future suggested research priorities include undertaking integrated studies on a range of species in the same landscapes; better documentation of the extent and duration of impact; and most importantly, combining neutral marker, pollination dynamics, ecological consequences, and progeny fitness assessment within single studies.

Factors influencing survival and long-term population viability of New Zealand long-tailed bats ( Chalinolobus tuberculatus): Implications for conservation

A population viability analysis is important for the management of endangered populations and requires the estimation of survival parameters. The long-tailed bat ( Chalinolobus tuberculatus) is one of only two native terrestrial mammals currently found in New Zealand and is classed as vulnerable. Its viability in temperate beech ( Nothofagus) forest, Eglinton Valley, Fiordland, New Zealand was estimated using mark-recapture data collected between 1993 and 2003 using the Program MARK. Survival was estimated based on a total of 5286 captures representing 1026 individuals. Overall annual survival varied between 0.34 and 0.83 but varied significantly among three sub-populations and with sex and age. Females generally had a higher survival rate compared to males; and adults had higher survival relative to juveniles. Survival of all bats was lower in years when the number of introduced mammalian predators was high and when the winter temperature was warmer than average. High numbers of introduced predators occurred during three of the 10 years in the study. Climate change may mean that the conditions that promote high predator numbers may occur more frequently. A preliminary population viability analysis using a projection matrix on the overall adult female population showed an average 5% decline per year ( λ = 0.95). Increased predator control targeting a range of predators is required in years when their numbers are high in order to halt the decline of this population of long-tailed bats. Population estimates using minimum number alive estimates supported the population estimates derived from Program MARK and a population viability analysis using matrices.

Demography and reproductive ecology of the Columbia spotted frog (Rana luteiventris) across the Palouse

Here we report on the demography and reproductive ecology of the Columbia spotted frog (Rana luteiventris Thompson, 1913) breeding in ponds across the Palouse Bioregion of Washington and Idaho. Spotted frogs are unusual, if not unique, among temperate ranids in that males establish the oviposition site before females become active. Females laid at one or two communal sites in shallow water. Our breeding populations were small, never exceeding 50 adults counted, and most displayed male-biased sex ratios. We estimated effective population sizes (Ne) as ranges determined by extremes in male breeding success; these varied between 3.2 and 37.8. Even the latter falls below the minimum required for long-term population viability. Small population size may make spotted frogs vulnerable to genetic problems and environmental insults. Communal oviposition certainly renders a population's reproductive effort vulnerable to variation in hydroperiod, which we observed during the dry spring of 2004. In the absence of information on the degree of "connectedness" among our ponds as subunits of more resilient metapopulations, we suggest that small population size and communal oviposition likely render R. luteiventris vulnerable to anthropogenic disturbance. Furthermore, the status of R. luteiventris on the Palouse may be less secure than assumed currently.

The effects of pastoralism and protection on the density and distribution of carnivores and their prey in the Mara ecosystem of Kenya

The overlap of large carnivores, livestock and people can engender conflicts that often threaten the future viability of carnivore populations in the pastoral systems of Africa. A playback survey of lions Panthera leo, spotted hyenas Crocuta crocuta and black-backed jackals Canis mesomelas and a transect count of wild herbivores was conducted in the Maasai Mara National Reserve and adjoining pastoral ranches to assess the effect of pastoralism and protection on the density and distribution of carnivores in June 2003. Reliability of the prey counts depended on an assumption of similar observability between the protected and pastoral areas, which we assessed using distance sampling in November 2003 and computer simulations and determined to be similar. Estimates of wild prey biomass density was 2.6 times higher in the ranches (14212 kg/km2) than in the reserve (5472 kg/km2) during this wet season count. Apparent hyena density estimates were 1.3 times higher in the ranches (0.561 hyenas/km2) than in the reserve (0.404 hyenas/km2), in correspondence with the regional pattern of prey density. This distribution of hyenas is biased towards the reserve, if it is dependent on prey density. Estimates of apparent jackal density were similar in both areas whereas lion density was anomalously 8.0 times lower in the ranches (0.046 lions/km2) than in the reserve (0.369 lions/km2). Lion and hyena densities and prey biomass did not differ between June 1991 (5172.273 kg/km2) and June 2003 (5472 kg/km2) in the reserve, but jackal density increased in the same period. Lions never responded to playbacks in the ranches, so the potential shift in lion behavioural response for different land use zones is another potential explanation for the patterns found here. We think a real shift in lion populations is a better explanation than a behavioural change in relation to playbacks based on additional data from independent systematic and intensive censuses and playback surveys conducted in the ranches. Lion populations in the pastoral ranches seemed headed for extinction, probably owing to conflicts with pastoralism, necessitating urgent conservation interventions that integrate pastoral economic welfare with large carnivore conservation goals to foster long-term viability of lion populations in the pastoral systems.

The effect of habitat fragmentation on communities of mutualists: Amazonian ants and their host plants

The consequences of fragmentation for communities of mutualist partners are for the most part unknown; moreover, most studies addressing this issue have been conducted on plant–pollinator communities. We evaluated how the experimental fragmentation of lowland Amazonian rain forest influenced a community of ant–plant mutualists. We inventoried a total of 1057 myrmecophytes in four fragments and four continuous forest sites; the twelve plant species recorded were occupied by 33 ant morphospecies, of which 11 were obligate plant inhabitants. Neither plant species richness, ant species richness, nor total ant–plant density were significantly lower in forest fragments. However, eight of the plant species, including three of the four most common, had higher mean densities in continuous forest than fragments. Of these four species, only one ( Cordia nodosa) had significantly different colonization rates between habitat types, with higher colonization rates of plants in fragments. This may be because the Azteca species it is associated with increases in abundance in forest isolates. Although our results suggest that communities of ant–plant mutualists are likely to persist in fragmented tropical landscapes 25 years after fragment isolation, most species are rare and populations sizes in fragments are extremely low. Environmental and demographic stochasticity could therefore limit long-term population viability. We suggest future studies focus on evaluating how fragmentation has altered herbivore pressure and the dispersal of ants and plants to fragments, since the interaction of these factors is likely to have the greatest impact on long-term patterns of population persistence.

NEST-SITE SELECTION PATTERNS AND THE INFLUENCE OF VEGETATION ON NEST SURVIVAL OF MIXED-GRASS PRAIRIE PASSERINES

Abstract Identification of habitat features influencing reproduction and survival are essential for the management and long-term viability of grassland bird populations. I quantified vegetation structure at nests and random sites in southern Saskatchewan, Canada, to determine which microhabitat features are important in nest-site selection by Sprague's Pipit (Anthus spragueii), Savannah Sparrow (Passerculus sandwichensis), Baird's Sparrow (Ammodramus bairdii), Chestnut-collared Longspur (Calcarius ornatus), and Western Meadowlark (Sturnella neglecta). In addition, I related microhabitat features to nest survival to determine whether predation might influence their choice of nest sites. Grassland passerines exhibited nonrandom nest-placement patterns and built their nests in sites that were characterized by a greater density of dead vegetation within 30 cm of the ground, increased amounts of litter, and reduced coverage of bare ground. In addition, each species nested in taller vegetation than that found a...

Diapause in Calanoid Copepods: within-clutch hatching patterns

Diapause is a major life history feature of many invertebrate organisms. Determining the phenology of diapause is critical for understanding survival and reproductive success of individuals as well as the long-term viability of many populations. The time spent in dormancy by individuals and variability among offspring in the duration of dormancy are two important aspects of invertebrate life histories. Some data are available, especially on duration of diapause, for plants and insects, but little information is available concerning variability among offspring in diapause traits. This is especially true for crustacean zooplankton, where essentially no information has been published on duration of diapause or variability among offspring in diapause timing or dynamics. Here I present data on the duration of diapause, and variability among offspring for diapause characteristics. The freshwater calanoid copepod Onychodiaptomus sanguineus, an obligately sexual species, was collected from Bullhead Pond, Rhode Island, U.S.A., and raised under conditions in the laboratory to induce production of diapausing eggs. One hundred clutches of these diapausing eggs (920 total eggs) were incubated for over two years in a full-factorial experiment testing the effects of temperature and photoperiod cycles on the hatching dynamics and duration of diapause. Overall hatching success was highest (approximately 86%) for eggs exposed to simultaneous temperature and photoperiod cycles mimicking natural changes, and was lowest (approximately 20%) when eggs were incubated at constant temperature (4 °C) and in constant dark conditions. The highest fraction of eggs hatched at approximately 550 days of age, but the age of eggs at hatching was highly variable among clutches. There was also large variability within clutches for hatching patterns, with some clutches containing eggs that all hatched synchronously and others in which eggs hatched more continuously throughout the experiment. Treatment conditions significantly affected within-clutch synchrony of hatching, as well as synchrony of the onset of hatching. These results of high within-clutch variability and differences among clutches in diapause dynamics have important implications for our understanding of reproductive success of individuals producing diapausing eggs, parent-offspring conflict, and the evolution of bet-hedging strategies in invertebrates.