Ensure Population Persistence Research Articles

Allometric relationships and trade-offs in 11 common Mediterranean-climate grasses.

Biomass allocation in plants is the foundation for understanding dynamics in ecosystem carbon balance, species competition, and plant-environment interactions. However, existing work on plant allometry has mainly focused on trees, with fewer studies having developed allometric equations for grasses. Grasses with different life histories can vary in their carbon investment by prioritizing the growth of specific organs to survive, outcompete co-occurring plants, and ensure population persistence. Further, because grasses are important fuels for wildfire, the lack of grass allocation data adds uncertainty to process-based models that relate plant physiology to wildfire dynamics. To fill this gap, we conducted a greenhouse experiment with 11 common California grasses varying in photosynthetic pathway and growth form. We measured plant sizes and harvested above- and belowground biomass throughout the life cycle of annual species, while for the establishment stage of perennial grasses to quantify allometric relationships for leaf, stem, and root biomass, as well as plant height and canopy area. We used basal diameter as a reference measure of plant size. Overall, basal diameter is the best predictor for leaf and stem biomass, height, and canopy area. Including height as another predictor can improve model accuracy in predicting leaf and stem biomass and canopy area. Fine root biomass is a function of leaf biomass alone. Species vary in their allometric relationships, with most variation occurring for plant height, canopy area, and stem biomass. We further explored potential trade-offs in biomass allocation across species between leaf and fine root, leaf and stem, and allocation to reproduction. Consistent with our expectation, we found that fast-growing plants allocated a greater fraction to reproduction. Additionally, plant height and specific leaf area negatively influenced the leaf-to-stem ratio. However, contrary to our hypothesis, there were no differences in root-to-leaf ratio between perennial and annual or C4 and C3 plants. Our study provides species-specific and functional-type-specific allometry equations for both above- and belowground organs of 11 common California grass species, enabling nondestructive biomass assessment in California grasslands. These allometric relationships and trade-offs in carbon allocation across species can improve ecosystem model predictions of grassland species interactions and environmental responses through differences in morphology.

Is it the road or the fence? Influence of linear anthropogenic features on the movement and distribution of a partially migratory ungulate

BackgroundAnthropogenic linear features change the behavior and selection patterns of species, which must adapt to these ever-increasing features on the landscape. Roads are a well-studied linear feature that alter the survival, movement, and distribution of animals. Less understood are the effects of fences on wildlife, though they tend to be more ubiquitous across the landscape than roads. Even less understood are potential indirect effects when fences are found in tandem with roads along transportation corridors.MethodsWe assessed how the spatial configuration of fences and roads effect the movement (crossing effect) and distribution (proximity effect) of a partially migratory pronghorn population (Antilocapra americana) on the grasslands of southern Alberta, Canada. We used data from 55 collared pronghorn within a step-selection function framework to assess the influence of 4 linear features: (1) pasture fences, (2) roads not fenced, (3) roads fenced on one side, and (4) roads fenced on both sides on the selection pattern of migratory and resident animals. We examined whether steps along a movement pathway (i.e., crossing effect) were influenced by the type of linear feature animals attempted to cross and, whether these features affected the distribution of pronghorn (i.e., proximity effect) across the landscape.ResultsThe top model for crossing effect for both movement tactics contained all 4 linear features and land cover. Regression coefficients were negative for all linear features, indicating that individuals were less likely to chose steps that crossed linear features. For the proximity effect, migrant animals avoided all linear features except roads fenced on both sides, where they selected areas closer to this feature. Resident animals, on the other hand, were found closer to pasture fences but further from roads without fences.ConclusionsOur results indicate that both fences and roads are indirectly affecting pronghorn resource use spatially and behaviorally, whether each linear feature is found separately or in tandem. Modifying existing fences and roads to account for responses to these distinct linear features could facilitate more successful crossing opportunities and/or shifts in distribution. Allowing pronghorn to freely move across the landscape will maintain functional connectivity to ensure population persistence of this endemic ungulate.

A mathematical model for the impact of noise on population dynamics of a single species experiencing Lombard effect

Noise is a form of pollution resulting from the undeniable increase in industrialization worldwide. Consequently, it is becoming increasingly important to understand the underlying mechanisms and potential effects of noise on ecosystems. In this study, we propose a deterministic mathematical model that uses a system of nonlinear, non-autonomous differential equations to describe the population dynamics of a single species exposed to noise. The Lombard effect is a phenomenon that involves increasing the intensity of acoustic signals in response to noise, which can mask and degrade acoustic signals and prevent them from being recognized or discriminated by their target receivers. However, when the anthropogenic noise is chronic and critical (i.e., that by its long duration and high intensity positively affects the mortality rate), the increase in the intensity of acoustic signals (due to the Lombard effect) only increases the chronic critical anthropogenic noise and also increase energetic, behavioral and predation costs. Therefore, the critical noise generated by the use of higher intensity acoustic signals (due to the Lombard effect) together with the chronic critical anthropogenic noise, negatively affect population survival. We analyzed the persistence of the population and found that our results are consistent with the observed ecological data as they suggest that, the maximum intensity level of critical chronic anthropogenic noise, consequently, by the Lombard effect, the maximum intensity of self generated acoustic signals, must decrease to ensure population persistence. However, when the maximum intensity level of critical chronic anthropogenic noise is uncontrollable, it is sufficient to reduce its mean intensity level to ensure persistence in the population mean. Furthermore, decreasing the degree to which noise affects the population favors the survival of the species. Finally, to validate our results, we performed numerical simulations.

The influence of spatial patterns in foraging habitat on the abundance and home range size of a vulnerable arboreal marsupial in southeast Australia

AbstractWildlife can persist in a range of landscape configurations, but population densities can vary due to resource availability. Resources and environmental conditions shaping habitat suitability may be spatially dispersed or clumped, which can drive habitat availability. We explored how spatial configuration and aggregation of favorable feeding resources and climatic conditions affect populations of the greater glider (Petauroides volans), an arboreal marsupial in southeast Australia, vulnerable to climate change and disturbances. We hypothesized home‐range functionality from literature and field observations and used a generalized spatial framework based on neutral landscape models to test how spatial aggregation influences home‐range sizes and population structure. At the landscape scale, any decrease in climatic suitability also decreased potential population density, independent of the initial spatial configuration of the feeding landscape. At the stand scale however, the spatial configuration of feeding habitat drove population density. Dispersed resources required increased home‐range sizes for individual greater gliders to obtain feeding resources and resulted in smaller populations. Clumped resources supported larger populations, even when only small fractions of the stand contained feeding habitat. Disturbances to these resources could either retain populations or lead to extinction, depending on spatial aggregation and disturbance intensity. Increasingly severe dispersed disturbances caused potential home ranges to disappear more rapidly and remaining home ranges to become larger and contain less feeding habitat. The ability of greater gliders to establish populations and persist under disturbance was therefore highly dependent on the spatial aggregation of habitat resources and the type and severity of disturbance. Changes in climate act at a different scale and may override favorable habitat conditions at the stand level. Our results have implications for the conservation and retention of critical feeding habitat for greater gliders and provide insights into important factors to ensure population persistence under climate change and forest management.

Terrestrial Morphotypes of Aquatic Plants Display Improved Seed Germination to Deal with Dry or Low-Rainfall Periods.

In temporary ponds, seed germination largely determines how well aquatic plant assemblages recover after dry periods. Some aquatic plants have terrestrial morphotypes that can produce seeds even in dry years. Here, we performed an experiment to compare germination patterns for seeds produced by aquatic and terrestrial morphotypes of Ranunculus peltatus subsp. saniculifolius over the course of five inundation events. During the first inundation event, percent germination was higher for terrestrial morphotype seeds (36.1%) than for aquatic morphotype seeds (6.1%). Seed germination peaked for both groups during the second inundation event (terrestrial morphotype: 47%; aquatic morphotype: 34%). Even after all five events, some viable seeds had not yet germinated (terrestrial morphotype: 0.6%; aquatic morphotype: 5%). We also compared germination patterns for the two morphotypes in Callitriche brutia: the percent germination was higher for terrestrial morphotype seeds (79.5%) than for aquatic morphotype seeds (41.9%). Both aquatic plant species use two complementary strategies to ensure population persistence despite the unpredictable conditions of temporary ponds. First, plants can produce seeds with different dormancy periods that germinate during different inundation periods. Second, plants can produce terrestrial morphotypes, which generate more seeds during dry periods, allowing for re-establishment when conditions are once again favorable.

Individual migration strategy fidelity but no habitat specialization in two congeneric seabirds

AbstractAimIn migratory species, individuals often use fixed and individual‐specific migration strategies, which we term individual migration strategy fidelity (IMSF). Our goal was to test if guillemots have flexible or fixed individual migration strategies (i.e. IMSF), if this behaviour is consistent across large parts of the genus’ range and if they were philopatric to geographical sites or a habitat feature.LocationNorth Atlantic.TaxonUria spp.MethodsWe quantified consistent individual differences in inter‐annual spatial distribution and habitat occupied throughout the non‐breeding period using a large geolocator tracking dataset of 729 adult seabirds breeding at 13 colonies across the Northeast Atlantic and repeatedly tracked up to 7 years over a 9‐year period. Additionally, we used a similarity index to calculate relative fidelity to either geographical sites or habitats and linear mixed‐effects models to assess persistence of spatial site fidelity over multiple years.ResultsBoth guillemot species exhibited IMSF across a large part of the genus’ range which persisted over multiple years. Individuals of both species and almost all colonies showed fidelity to geographical sites and not to specific habitats.Main conclusionsGuillemots show IMSF that is best explained by site familiarity (fidelity to specific sites) rather than habitat specialization (fidelity to specific habitats). In the context of rapidly changing environments, favourable habitats may permanently shift locations and hence species displaying IMSF driven by site familiarity—such as the genus Uria—may not be able to adjust their migration strategies sufficiently fast to sustain individual fitness and ensure population persistence.

Sustainability management of short-lived freshwater fish in human-altered ecosystems should focus on adult survival.

Fish populations globally are susceptible to endangerment through exploitation and habitat loss. We present theoretical simulations to explore how reduced adult survival (age truncation) might affect short-lived freshwater fish species in human-altered contemporary environments. Our simulations evaluate two hypothetical "average fish" and five example fish species of age 1 or age 2 maturity. From a population equilibrium baseline representing a natural, unaltered environment we impose systematic reductions in adult survival and quantify how age truncation affects the causes of variation in population growth rate. We estimate the relative contributions to population growth rate arising from simulated temporal variation in age-specific vital rates and population structure. At equilibrium and irrespective of example species, population structure (first adult age class) and survival probability of the first two adult age classes are the most important determinants of population growth. As adult survival decreases, the first reproductive age class becomes increasingly important to variation in population growth. All simulated examples show the same general pattern of change with age truncation as known for exploited, longer-lived fish species in marine and freshwater environments. This implies age truncation is a general potential concern for fish biodiversity across life history strategies and ecosystems. Managers of short-lived, freshwater fishes in contemporary environments often focus on supporting reproduction to ensure population persistence. However, a strong focus on water management to support reproduction may reduce adult survival. Sustainability management needs a focus on mitigating adult mortality in human-altered ecosystems. A watershed spatial extent embracing land and water uses may be necessary to identify and mitigate causes of age truncation in freshwater species. Achieving higher adult survival will require paradigm transformations in society and government about water management priorities.

Population Viability of Endangered Lost River Sucker and Shortnose Sucker and the Effects of Assisted Rearing

Abstract The Lost River Sucker Deltistes luxatus and Shortnose Sucker Chasmistes brevirostris are two narrowly endemic fish species in the upper Klamath Basin of southern Oregon and northern California. Both species have been federally listed as endangered pursuant to the U.S. Endangered Species Act since 1988 because of dramatic declines in abundance and distribution. In Upper Klamath Lake, Oregon, both species have only recruited a single cohort to the adult populations since that time. Most individuals in this population are at or older than the expected life span of the species. Consequently, the U.S. Fish and Wildlife Service and the Klamath Tribes have initiated assisted rearing efforts to stabilize the population. However, it is unclear how quickly these populations might become extirpated and how assisted rearing might alter population trajectories. We modeled the potential for extinction and recovery of the populations of endangered Lost River Sucker and Shortnose Sucker in Upper Klamath Lake. We simulated population trajectories over the next 50 y with a stochastic population viability assessment approach. Projections indicate that if population trajectories do not change, the Shortnose Sucker population may decline by 78% to number < 5,000 in 10 y and become completely extirpated within the next 30 (18.6% probability) to 40 y (99% probability). The two Lost River Sucker populations have a greater likelihood to remain extant after 50 y, with only 1% probability of extinction given our scenarios and assumptions, but the populations are likely to number fewer than 1,000 individuals. Our results also suggest that rearing of Klamath Lake sucker species in a controlled environment for augmenting the natural population will be effective in reducing extirpation probabilities over the next 50 y if survival to recruitment can be achieved, but a long-term effort of at least 40 y will be required. The necessity of long-term augmentation to ensure population persistence in the absence of natural recruitment underscores the urgent need to determine and address the causes of recruitment failure in the wild.

Evaluating the Trade‐Offs between Invasion and Isolation for Native Brook Trout and Nonnative Brown Trout in Pennsylvania Streams

AbstractA popular conservation strategy for native trout species in western North America is to prevent invasions by nonnative trout by installing barriers that isolate native trout populations into headwater streams. In eastern North America, native Brook Trout Salvelinus fontinalis are frequently replaced in coolwater habitats by nonnative Brown Trout Salmo trutta and relegated to small headwater streams. In this study, we compared the effects of isolation and invasion by nonnative Brown Trout on the distribution and demographic structure of Brook Trout populations from 78 trout streams in northwestern Pennsylvania. The Brook Trout and Brown Trout distributions varied in predictable ways along the stream size gradient, with Brown Trout becoming dominant in larger streams. However, there was a prominent barrier effect, with streams 12 times more likely to have Brook Trout than Brown Trout when a downstream barrier was present between the sample site and the nearest Brown Trout stocking location. In comparison, 91% of the streams with Brown Trout had no downstream barrier, suggesting that barriers are important in creating refugia for Brook Trout. Brown Trout also appeared to have a negative impact on Brook Trout population demographics, as Brook Trout populations in sympatry with Brown Trout had fewer age‐classes and lower population densities than allopatric Brook Trout populations. Isolating Brook Trout to small headwater streams with downstream barriers that prevent Brown Trout invasion could be a viable conservation strategy in regions where barriers would serve to reduce the negative impacts from Brown Trout. Since barriers could further fragment local Brook Trout populations, however, they would need to be strategically placed to allow for seasonal movements to maintain metapopulation structure and ensure population persistence.

Reproductive state leads to intraspecific habitat partitioning and survival differences in greater sage-grouse: implications for conservation

Context Inter- and intraspecific habitat partitioning is widespread across taxa, yet limited information is available on differences in intraspecific habitat selection by same-sex individuals among differing reproductive states. Understanding habitat selection by conspecifics of different reproductive states may help optimise conservation efforts, particularly for gallinaceous bird species such as greater sage-grouse (Centrocercus urophasianus), which are long-lived but have only moderate reproductive rates. Aims We predicted that habitat use differed between grouse under different reproductive states and that reproductive investment decreased survival of adults in summer. Methods We compared habitat characteristics used by brood-rearing and broodless female sage-grouse and evaluated the influence of reproductive investment and habitat use on survival of adult females. Key results We found that brood-rearing and broodless female sage-grouse partitioned habitat at micro- and macrohabitat scales. Broodless females were more likely to survive the summer. Conclusions Our findings suggest reproductive state variability in habitat selection by female sage-grouse. Broodless females were roosting and foraging in concealed habitats with intermediate visual obstruction and annual vegetation productivity, but less food forb availability compared with early and late brood-rearing females. In contrast, brood-rearing females likely selected more herbaceous understoreys to predictably maximise foraging opportunities and promote growth of their chicks, which appeared to mitigate the influence of reproductive costs on summer survival, particularly during the late brood-rearing period. Implications Survival of adult females is critical for population persistence of sage-grouse and other long-lived Galliformes, yet conservation efforts generally focus on habitats used during nesting and brood-rearing. Our results suggest that habitat partitioning is a potential risk-aversion strategy where individuals across different reproductive states likely select habitats to maximise their survival. Conservation efforts should focus on conserving habitats used by both brood-rearing and broodless sage-grouse to ensure population persistence.

Increased drought frequency alters the optimal management strategy of an endangered plant

Many rare plant and animal species require frequent habitat disturbance to ensure population persistence, but humans often suppress or modify natural disturbance regimes, such as floods and fires, which harms disturbance-adapted species. To manage these populations, demographic models are often used to quantify the optimal disturbance frequency of the habitat. Increasing drought frequency due to climate change could alter optimal management strategies by decreasing the benefit of a recently disturbed habitat. We ask whether disturbance and drought interactively affect population dynamics and optimal management of Astragalus bibullatus, a Federally endangered legume endemic to limestone cedar glades in Tennessee. We used matrix population models to determine the independent and interactive effects of drought and management of woody canopy cover on A. bibullatus' probability of extinction, time to extinction and future population size. Under current drought frequencies, A. bibullatus' probability of extinction was minimized with the most frequent management, since open habitats promote recruitment. However, as drought frequency increases, the probability of extinction was minimized with less frequent management, since canopy cover decreased mortality of older plants during droughts. We recommend managing disturbance-dependent habitats by maintaining two types of environments; those that promote high survivorship during climatically unfavorable years, and those that promote increased reproduction and recruitment during climatically favorable years. Varying management goals across the landscape will decrease species-wide risk by preventing a single drought from harming all populations.

Assessing reserve effectiveness: Application to a threatened species in a dynamic fire prone forest landscape

Reserve systems are part of biodiversity conservation planning. However, reserves are rarely assessed for their contribution to population persistence. Here we address knowledge gaps on reserve effectiveness by developing a new approach to model protected area efficacy as a function of habitat suitability and natural disturbance regimes. We demonstrate the utility of the model through a detailed case study of the critically endangered Leadbeater⿿s possum (Gymnobelideus leadbeateri) in south⿿eastern Australia. We defined reserve effectiveness for the species to be when there was no more than 5% probability of populations falling to (or below) 500 adult females in 40 generations. A reserve system established specifically for Leadbeater⿿s possum was found inadequate to ensure population persistence for the next 40 generations, given historical disturbance, habitat decline, and future fires. Simulation modelling of potential areas of reserve suggests that, depending on management risk tolerance, between 30% to 100% of current forest extent within the range of the species may be required to ensure population persistence. This study exemplifies the need to consider the size of reserves prior to their establishment to ensure an adequate reserve design that will be effective against future disturbance for conserving threatened species.

Growth and reproduction of the highfin grouper Epinephelus maculatus.

Highfin grouper Epinephelus maculatus sampled in Chuuk, Micronesia, exhibited a moderate growth rate and a relatively short life span compared to other epinephelids of a similar size. Combined gonad and otolith analysis provide preliminary evidence that the species conforms to a protogynous sexual pattern. Mean total length at maturity for females was 308 mm with first age at maturity 2·8 years for females and 4 years for males, which differs from other regional studies. Based on the gonado-somatic index and microscopic analysis of gonads, E. maculatus in Chuuk have a 4 month spawning season (January to April) that corresponds with seasonal lows in sea surface water temperature and overlaps with that of other aggregating epinephelids. The estimated von Bertalanffy growth factor (K) was 0·51 year(-1) , while total mortality was 0·34 year(-1) . Current management for E. maculatus in Chuuk includes a January to May catch, sale and export ban, which overlaps with its reproductive season. The effectiveness of these arrangements will require on-going monitoring to determine whether alternative management strategies are required to ensure population persistence.

Habitat fragmentation in coastal southern California disrupts genetic connectivity in the cactus wren (Campylorhynchus brunneicapillus).

Achieving long-term persistence of species in urbanized landscapes requires characterizing population genetic structure to understand and manage the effects of anthropogenic disturbance on connectivity. Urbanization over the past century in coastal southern California has caused both precipitous loss of coastal sage scrub habitat and declines in populations of the cactus wren (Campylorhynchus brunneicapillus). Using 22 microsatellite loci, we found that remnant cactus wren aggregations in coastal southern California comprised 20 populations based on strict exact tests for population differentiation, and 12 genetic clusters with hierarchical Bayesian clustering analyses. Genetic structure patterns largely mirrored underlying habitat availability, with cluster and population boundaries coinciding with fragmentation caused primarily by urbanization. Using a habitat model we developed, we detected stronger associations between habitat-based distances and genetic distances than Euclidean geographic distance. Within populations, we detected a positive association between available local habitat and allelic richness and a negative association with relatedness. Isolation-by-distance patterns varied over the study area, which we attribute to temporal differences in anthropogenic landscape development. We also found that genetic bottleneck signals were associated with wildfire frequency. These results indicate that habitat fragmentation and alterations have reduced genetic connectivity and diversity of cactus wren populations in coastal southern California. Management efforts focused on improving connectivity among remaining populations may help to ensure population persistence.

More rapid climate change promotes evolutionary rescue through selection for increased dispersal distance

Species can either adapt to new conditions induced by climate change or shift their range in an attempt to track optimal environmental conditions. During current range shifts, species are simultaneously confronted with a second major anthropogenic disturbance, landscape fragmentation. Using individual-based models with a shifting climate window, we examine the effect of different rates of climate change on the evolution of dispersal distances through changes in the genetically determined dispersal kernel. Our results demonstrate that the rate of climate change is positively correlated to the evolved dispersal distances although too fast climate change causes the population to crash. When faced with realistic rates of climate change, greater dispersal distances evolve than those required for the population to keep track of the climate, thereby maximizing population size. Importantly, the greater dispersal distances that evolve when climate change is more rapid, induce evolutionary rescue by facilitating the population in crossing large gaps in the landscape. This could ensure population persistence in case of range shifting in fragmented landscapes. Furthermore, we highlight problems in using invasion speed as a proxy for potential range shifting abilities under climate change.

Subpopulation range estimation for conservation planning: a case study of the critically endangered Cross River gorilla

Measuring and characterizing the area utilized by a population or species is essential for assessment of conservation status and for effective allocation of habitat to ensure population persistence. Yet population-level range delineation is complicated by the variety of available techniques coupled with a lack of empirical methods to compare the relative value of these techniques. This study assesses the effect of model choice on resulting subpopulation range estimation for the critically endangered and patchily distributed Cross River gorilla, and evaluates the conservation conclusions that can be drawn from each model. Models considered range from basic traditional approaches (e.g. minimum convex polygon) to newer home range techniques such as local convex hull (LoCoH). Overlap analysis comparing sub-sampled to complete data sets are used to evaluate the robustness of various modeling techniques to data limitations. Likelihood cross validation criterion is employed to compare core range model performance. Results suggest that differing LoCoH models produce similar range estimates, are robust to data requirements, provide a good fit for core habitat estimation, and are best able to detect unused habitat within the subpopulation range. LoCoH methods may thus be useful for studies into habitat selection and factors limiting endangered species distributions. However, LoCoH models tend to over-fit data, and kernel methods may provide similar information about animal space use while supporting protection of larger swaths of critical habitat. Subpopulation range analyses for conservation/management planning should therefore explore multiple modeling techniques, and employ both qualitative and quantitative assessments to select the best models to inform decision making for species of conservation concern.

A spatial analytical approach for selecting reintroduction sites for burbot in English rivers

1.?Availability of suitable habitat is a prerequisite for species reintroduction success, and to ensure population persistence, investigations of a species’ habitat utilisation throughout its life history should be conducted as part of a feasibility study. 2.?Habitat utilisation models for burbot, Lota lota, developed using data from field studies conducted in France and Germany and information from the literature were used to assess the feasibility of reintroducing burbot into rivers of its former native range in eastern England. 3.?Per cent tree roots, aquatic vegetation and flow types were important predictors of adult burbot abundance. Furthermore, the habitat utilisation models were supplemented with information from the literature, which suggested that off-channel habitat such as wetlands and backwaters is important for spawning and nursery stages. 4.?An assessment of the habitat availability in the rivers of the burbot’s former native range using variables related to spawning and nursery and adult life stages showed that although adult habitat was widely distributed, the availability of spawning and nursery habitat was less abundant, potentially limiting successful reestablishment. 5. ?Potential suitable habitat was concentrated in the central and southern areas of the species’ former English distribution. Overall, rivers of the burbot’s former range potentially afford suitable habitat to sustain a reintroduced population. However, sites should be preferentially selected on the basis of having appropriate spawning and nursery areas

Genetic erosion impedes adaptive responses to stressful environments.

Biodiversity is increasingly subjected to human-induced changes of the environment. To persist, populations continually have to adapt to these often stressful changes including pollution and climate change. Genetic erosion in small populations, owing to fragmentation of natural habitats, is expected to obstruct such adaptive responses: (i) genetic drift will cause a decrease in the level of adaptive genetic variation, thereby limiting evolutionary responses; (ii) inbreeding and the concomitant inbreeding depression will reduce individual fitness and, consequently, the tolerance of populations to environmental stress. Importantly, inbreeding generally increases the sensitivity of a population to stress, thereby increasing the amount of inbreeding depression. As adaptation to stress is most often accompanied by increased mortality (cost of selection), the increase in the ‘cost of inbreeding’ under stress is expected to severely hamper evolutionary adaptive processes. Inbreeding thus plays a pivotal role in this process and is expected to limit the probability of genetically eroded populations to successfully adapt to stressful environmental conditions. Consequently, the dynamics of small fragmented populations may differ considerably from large nonfragmented populations. The resilience of fragmented populations to changing and deteriorating environments is expected to be greatly decreased. Alleviating inbreeding depression, therefore, is crucial to ensure population persistence.

Seasonal Influences on Population Spread and Persistence in Streams: Critical Domain Size

The critical domain size problem determines the size of the region of habitat needed to ensure population persistence. In this paper we address the critical domain size problem for seasonally fluctuating stream environments and determine how large a reach of suitable stream habitat is needed to ensure population persistence of a stream-dwelling species. Two key factors, not typically found in critical domain size problems, are fundamental in determining whether population can persist. These are the unidirectional nature of stream flow and seasonal fluctuations in the stream environment. We characterize the fluctuating environments in terms of seasonal correlations among the flow, transfer rates, diffusion, and settling rates, and we investigate the effect of such correlations on the critical domain size problem. We show how results for the seasonally fluctuating stream can formally be connected to those for autonomous integro-differential equations, through the appropriate weighted averaging methods.

Evidence of age-class truncation in some exploited marine fish populations in New South Wales, Australia

Exploited reef-associated species in south-eastern Australia have evolved life-history strategies to ensure population persistence through periods that are unsuitable for recruitment. They are characterized by considerable potential longevity (20–50 years), sexual maturation at relatively young ages (2–4 years old) and variable recruitment patterns. The age compositions in landings of the major reef-associated species in this region were used to demonstrate that some species have been subjected to significant age-class truncation. Species with long histories of exploitation had age compositions with relatively few fish greater than 5 years old. It is suggested that the removal of older age classes from the most heavily exploited populations has lowered their resilience to environmental change and that remedial management action may be required to rebuild reserves of older individuals. It is argued that the management options that are most likely to succeed in achieving this objective for populations of offshore reef-associated species include reducing rates of exploitation to very low levels, protecting larger/older fish through regulated maximum length limits and/or changes to gear selectivity and no take marine protected areas. The most appropriate management options will depend on the life-history of the species being considered.