A Neglected Science: Applying Behavior to Aquatic Conservation

Behavioral theories, insights, and techniques are too frequently ignored by conservation biologists. Yet an animal's survival and reproductive success clearly depend on its behavior. Using examples from marine, freshwater, and terrestrial realms, I assert that behavioral information is invaluable in five conservation areas: (1) managing wild species (e.g., designing marine reserves; reducing animal–human conflicts; understanding and managing species' responses to human-induced environmental stress such as fishing, introduced species, and chemical, visual, and acoustic pollution); (2) actively reversing the decline of imperiled wild species (e.g., reducing bycatch by improving selectivity of fishing gear; re-establishing breeding populations and boosting reproduction); (3) assessing biodiversity (e.g., modeling population viability; censusing and monitoring populations and species); (4) captive breeding and reintroduction programs (e.g., minimizing loss of valuable phenotypes; teaching or maintaining valuable survival skills); and (5) changing human behavior in resource exploitation (e.g., using principles from social psychology). Both realized and potential applications to fishes are stressed. Finally, behavioral diversity, a valuable but neglected element of biodiversity, needs to be explicitly conserved to maintain diverse populations. Arguments are presented that the conservation of species diversity and genetic diversity alone does not necessarily protect important behavioral diversity. The maintenance of both individual and population variability may be essential for the preservation of a species.     

Pollution of the sea and its effects.

Marine pollution has been studied under the following groupings of effects; harm to living resources, hazards to human health, reduction of amenities and interference with other users of the sea. This paper is concerned mainly with the first two categories and their interrelation. Apart from certain seabirds affected by oil, the major stocks of marine animals show no evidence of reduction by pollution. Pollution effects are generally insignificant in relation to other factors governing reproductive success, survival, growth and population size. Even in the North Sea, which has received a greatly increased pollution load during the last three decades, both total production of fish and catch per unit of effort (a measure of abundance) of cod, haddock and plaice increased during the 20 years 1950--69. Very recent decreases have been due to over-exploitation but, except in certain estuaries and immediate coastal waters, direct damage by pollution to marine populations and ecosystems is not evident. Pollution effects can, however, be detected by chemical analysis. The paper examines human health risks arising in the marine environment, particularly from contaminated seafood, especially in relation to sewage pollution, metals such as mercury, cadmium and lead, synthetic organic substances and oil.     

Chemical interactions in diatoms: role of polyunsaturated aldehydes and precursors

Chemicals produced by aquatic organisms, and especially micro-organisms, have received increasing attention in the last decade for their role in shaping interactions and communities. Several cases emphasize the fact that chemical signals or defence may modulate interspecific interactions. Notably, it has been shown that diatoms, unicellular algae and key primary producers in aquatic ecosystems produce a wide range of bioactive metabolites. Among these compounds, polyunsaturated short-chain aldehydes in vitro strongly impair the reproduction of various potential grazers. In the field, the relationship between aldehyde production and reproductive failure in copepods remains unclear. Recent studies have suggested that these putative defence compounds may also be involved in intercellular communication and in interactions with competitors. Potential effects of the aldehyde precursors on various organisms have also been described. This review presents an overview of various results obtained in the last decade that could help us to understand the role of polyunsaturated aldehydes and their precursors in the ecology of diatoms. It is focused on the dichotomy between freshwater and marine environments. Indeed, most of the results on anti-proliferative aldehydes concern marine planktonic diatoms, whereas they are also known to be produced by benthic and freshwater species.     

The eco-evolutionary importance of reproductive system variation in the macroalgae: Freshwater reds as a case study

The relative frequency of sexual versus asexual reproduction governs the distribution of genetic diversity within and among populations. Most studies on the consequences of reproductive variation focus on the mating system (i.e., selfing vs. outcrossing) of diploid-dominant taxa (e.g., angiosperms), often ignoring asexual reproduction. Although reproductive systems are hypothesized to be correlated with life-cycle types, variation in the relative rates of sexual and asexual reproduction remains poorly characterized across eukaryotes. This is particularly true among the three major lineages of macroalgae (green, brown, and red). The Rhodophyta are particularly interesting, as many taxa have complex haploid–diploid life cycles that influence genetic structure. Though most marine reds have separate sexes, we show that freshwater red macroalgae exhibit patterns of switching between monoicy and dioicy in sister taxa that rival those recently shown in brown macroalgae and in angiosperms. We advocate for the investigation of reproductive system evolution using freshwater reds, as this will expand the life-cycle types for which these data exist, enabling comparative analyses broadly across eukaryotes. Unlike their marine cousins, species in the Batrachospermales have macroscopic gametophytes attached to filamentous, often microscopic sporophytes. While asexual reproduction through monospores may occur in all freshwater reds, the Compsopogonales are thought to be exclusively asexual. Understanding the evolutionary consequences of selfing and asexual reproduction will aid in our understanding of the evolutionary ecology of all algae and of eukaryotic evolution generally.     

滩涂底栖动物有机污染生态学研究进展

底栖动物由于对有机污染物具有较强的吸收能力,再加上其移动能力较差、生活方式比较固定,而被广泛运用于滩涂有机污染的研究.目前这些研究主要集中在如下几个方面：（1）有机污染物在底栖动物体内的分布特征及在底栖食物链中的动力学研究;（2）底栖动物对有机污染物的生理响应研究;（3）污染物对底栖动物群落组成和结构影响研究;（4）底栖动物在滩涂有机污染检测中的应用研究.研究结果表明：滩涂底栖动物对有机污染物的累积具有选择性和季节波动性;有机污染物可以在底栖食物链中传递;底栖动物体内的有机污染物成分和含量可以有效地指示其生存环境的有机污染状况;底栖动物的混合功能氧化酶和抗氧化酶系统对体内有机污染物的累积产生积极的响应;有机污染物对底栖动物的免疫系统造成不利影响,并对遗传物质造成破坏;有机污染对底栖动物的群落组成和结构具有显著的影响.     

Adaptive reproductive variation along a pollution gradient in a wolf spider

When populations are exposed to environmental pollutants, growth and reproduction might be strongly reduced due to an increased detoxification effort. Sublethal metal pollution is therefore to be expected to cause the same selection pressure as a low resource habitat and might alter the reproductive strategy. Optimality models of life history theory predict that when resource availability is reduced, growth and reproductive output are reduced and that the release of fewer but larger propagules will be favoured. This was tested by applying a life history model to reproductive trait measurements in six populations of the wolf spider Pirata piraticus in which the assumptions of the model are satisfied. Internal Cd, Cu and Zn body burden were strongly correlated with each other, and differed strongly between the populations, indicating consistently differing metal exposure at the different sites. Pb levels were extremely variable within each population and did not differ between the populations. Females from populations with high concentrations of the first three heavy metals showed a strongly reduced reproductive output and fecundity, indicating a high reduction in resource availability due to detoxification processes. Egg size in contrast was negatively correlated with fecundity and reproductive output and as a consequence positively related with internal metal burden. Our results are thus in strong agreement with the predictions of the optimality models and confirm the benefits of a larger propagule size when resource availability is reduced.     

Demographic consequences of heavy metals and persistent organic pollutants in a vulnerable long-lived bird,the wandering albatross

Seabirds are top predators of the marine environment that accumulate contaminants over a long life-span. Chronic exposure to pollutants is thought to compromise survival rate and long-term reproductive outputs in these long-lived organisms, thus inducing population decline. However, the demographic consequences of contaminant exposure are largely theoretical because of the dearth of long-term datasets. This study aims to test whether adult survival rate, return to the colony and long-term breeding performance were related to blood mercury (Hg), cadmium (Cd) and persistent organic pollutants (POPs), by using a capture–mark–recapture dataset on the vulnerable wandering albatross Diomedea exulans. We did not find evidence for any effect of contaminants on adult survival probability. However, blood Hg and POPs negatively impacted long-term breeding probability, hatching and fledging probabilities. The proximate mechanisms underlying these deleterious effects are likely multifaceted, through physiological perturbations and interactions with reproductive costs. Using matrix population models, we projected a demographic decline in response to an increase in Hg or POPs concentrations. This decline in population growth rate could be exacerbated by other anthropogenic perturbations, such as climate change, disease and fishery bycatch. This study gives a new dimension to the overall picture of environmental threats to wildlife populations.     

Genotoxic, carcinogenic, and teratogenic hazards in the marine environment, with special reference to the Mediterranean Sea.

Genotoxic, carcinogenic, and teratogenic hazards arising out of pollution in the marine environment are discussed in this article, with special reference to the situation in the Mediterranean area. A number of chemical compounds or complex mixtures relevant to marine pollution, either natural or of anthropogenic origin, are tentatively listed, along with protective factors which may play a counteracting role in the same environment. Harmful substances tend to undergo interactions and transformations in seawater, sediments, and marine biota, due to physical, chemical, microbial, or light-mediated mechanisms. Bioaccumulation phenomena in marine organisms may result from food-chain biomagnification processes or from concentration of pollutants by filter feeders. A variety of sources can account for marine pollution by genotoxic, carcinogenic, and teratogenic compounds, but there is a relative paucity of analytical data concerning the Mediterranean. Metabolic transformations of xenobiotics occur in all marine organisms, the biochemical mechanisms in fish being comparable to those which have been extensively investigated in mammals. Induction of metabolic pathways, and especially of the mixed-function oxygenase system, represents the earliest warning signal of exposure to pollutants. Occurrence of neoplastic diseases is documented by experimental and field studies in marine vertebrates as well as in invertebrates. The association with local pollution phenomena has been recognized in several studies, but other etiopathogenetic factors may be also involved, and in some cases tumors have been reported to be unrelated to chemical pollution. Genotoxic agents have been detected by means of suitable techniques in seawater, sediments, and marine organisms. Several studies have investigated the presence of carcinogen-DNA adducts, DNA damage and repair processes, and cytogenetic alterations, such as chromosomal aberrations, sister-chromatid exchanges, and micronuclei, in tissues of marine organisms. However, monitoring of these end-points under field conditions encounters some limitations and problems. Even more fragmentary is the information on teratogenic effects in marine organisms, although interesting test systems have been set up. On the whole, a quite extensive database on all these toxicological issues is already available in the literature, but further studies are warranted for an adequate assessment of genotoxic, carcinogenic, and teratogenic hazards, and possibly counteracting factors in the marine environment, and specifically in the Mediterranean Sea.     

Mechanisms of reproductive compensation in populations with different types of reproduction

Reproductive compensation mechanisms have been studied in two populations with different reproductive behaviour. In populations with natural reproductive behaviour mechanism of reproductive compensation was shown to be the shortening of the mean intergenetic interval in the female group having excessive (as compared with the mean population value) failures in their pregnancy outcomes (spontaneous abortions, still-births, prereproductive age deaths of children). In family planning populations, however, reproductive compensation mechanisms are: deliberate shortening of the intergenetic interval after pregnancy failure only and deliberate prolongation of actual reproduction. In family planning populations the proportion of females bearing at over 35 was shown to double, due to reproductive compensation.     

Plastic reproductive allocation as a buffer against environmental stochasticity – linking life history and population dynamics to climate

Empirical work suggest that long‐lived organisms have adopted risk sensitive reproductive strategies where individuals trade the amount of resources spent on reproduction versus survival according to expected future environmental conditions. Earlier studies also suggest that climate affects population dynamics both directly by affecting population vital rates and indirectly through long‐term changes in individual life histories. Using a seasonal and state‐dependent individual‐based model we investigated how environmental variability affects the selection of reproductive strategies and their effect on population dynamics. We found that: (1) dynamic, i.e. plastic, reproductive strategies were optimal in a variable climate. (2) Females in poor and unpredictable climatic regimes allocated fewer available resources in reproduction and more in own somatic growth. This resulted in populations with low population densities, and a high average female age and body mass. (3) Strong negative density dependence on offspring body mass and survival, along with co‐variation between climatic severity and population density, resulted in no clear negative climatic effects on reproductive success and offspring body mass. (4) Time series analyses of population growth rates revealed that populations inhabiting benign environments showed the clearest response to climatic perturbations as high population density prohibited an effective buffering of adverse climatic effects as individuals were not able to gain sufficient body reserves during summer. Regularly occurring harsh winters ‘harvested’ populations, resulting in persistent low densities, and released them from negative density dependent effects, resulting in high rewards for a given resource allocation.     

Review on the effects of pollution on marine fish life and fisheries in the North Sea

Information on possible effects of pollution on fish life is reviewed with special emphasis to the North Sea. Concentrations of heavy metals are high in onshore waters, sediments and organisms. Offshore regions are considered to be not endangered. In estuaries concentrations of certain heavy metals are often surpassing thresholds, which have been experimentally demonstrated to produce sublethal effects on marine organisms. Also mussel culture areas had to be closed due to excess of cadmium contamination. Mercury in fillets of cod in the southern North Sea sometimes reaches 0.3 ppm representing 1/3 of the legal limit. Reductions of inputs are necessary due to the bioaccumulative and toxic potential of heavy metals. Organochlorine contamination of water, sediments and organisms is higher in the southern than in the northern North Sea. In offshore areas clearly elevated levels of PCB's, which are the dominating organochlorine compound in marine organisms, have been analyzed. At present only a minor fraction of total organochlorine residues accumulated in marine biota is analyzed. Margins between experimentally derived lethal levels and those occurring in marine biota are narrow suggesting that sublethal effects might occur. One of the special concerns in the context of organochlorine contamination has to be seen in the potential of these substances affecting the reproductive capacity of marine organisms. Reduction measures are urgently necessary and should include substances with bioaccumulative and toxicological potential, which are not presently included in Marine Monitoring Programmes. Impact of oil pollution is considered to be a regional problem, although especially in estuaries concentrations in the water column might be high. Input through oil platforms has led to local reductions in benthic communities. Measures have to be taken, to further reduce these inputs also in view to avoid contamination of fish in the vicinity of oil fields. Oxygen depletion in German and Danish coastal waters has been shown to be a severe degradation in coastal water quality resulting in significant impact on fish populations. Indications for large-scale avoidance reactions of low DO-areas and mortalities of fish and benthos organisms have been demonstrated. It is suspected that the low DO-situations are related to increased nutrients input and high phytoplankton production. Improvement of the situation can only be expected, if input of nutrients is reduced. Reasons for the occurrence of toxic plankton blooms are not understood. An intensified research is necessary, to avoid damage to fisheries and mariculture. Although activity of radionucleids in North Sea waters is increased due to input of radioactive material from La Hague and Sellafield reprocessing units, the present levels of activity are not considered to be a threat for marine life. The same holds for thermal pollution, which is, depending on the recipient area, expected to have only local effects. Sewage sludge dumping and discharge of untreated sewage introduce significant amounts of accompanying heavy metals, which can be expected to have a negative influence on the total metal budget of recipient waters. Nutrient input through sewage will exhibit only local effects. Dumping of wastes from titanium dioxide industry are suspected to be causally linked to the occurrence of increased prevalences of certain diseases of dab in the German Bight. Present management strategies should take account of the fact that through dumping of waste from titanium dioxide production significant quantities of heavy metal are introduced into the southern North Sea. Also the incineration of chemical wastes at sea should be reduced due to uncertainties concerning quantities and toxicity of incineration products and their potential impact on marine life. It is concluded that clear evidence exists for pollution impact in estuarine regions. Most of the major estuaries at the North Sea coast show benthos reductions, which can be related to water quality and it has to be assumed that areas of a sublethal effect are located in the vicinity of those areas of well demonstrated effects. They are of unknown size and attempts have to be undertaken to quantify areas of sublethal impact. The occurrence of fish diseases is interpreted as an expression of degraded water quality. Some of the diseases detected can produce mortality, thereby having an as yet unquantified impact on fish populations. The presence of fish diseases also reduces the marketability of catches. It cannot be excluded that changes in species composition of fish populations in German Wadden Sea areas are related to pollution. Concentrations of organochlorine substances in fishes of the southern North Sea give rise to the concern that their reproductive capability might be impaired. Future work has to be directed to this problem. Impact of pollution on populations of marine organisms has so far not been demonstrated.     

Evolutionary divergence and possible incipient speciation in post-glacial populations of a cosmopolitan aquatic plant

Habitat configuration is expected to have a major influence on genetic exchange and evolutionary divergence among populations. Aquatic organisms occur in two fundamentally different habitat types, the sea and freshwater lakes, making them excellent models to study the contrasting effects of continuity vs. isolation on genetic divergence. We compared the divergence in post-glacial populations of a cosmopolitan aquatic plant, the pondweed Potamogeton pectinatus that simultaneously occurs in freshwater lakes and coastal marine sites. Relative levels of gene flow were inferred in 12 lake and 14 Baltic Sea populations in northern Germany using nine highly polymorphic microsatellite markers developed for P. pectinatus. We found highly significant isolation-by-distance in both habitat types (P < 0.001). Genetic differentiation increased approximately 2.5-times faster among freshwater populations compared with those from the Baltic Sea. As different levels of genetic drift or population history cannot explain these differences, higher population connectivity in the sea relative to freshwater populations is the most likely source of contrasting evolutionary divergence. These findings are consistent with the notion that freshwater angiosperms are more conducive to allopatric speciation than their life-history counterparts in the sea, the relative species poor seagrasses. Surprisingly, population pairs from different habitat types revealed almost maximal genetic divergence expected for complete reproductive isolation, regardless of their respective geographical distance. Hence, the barrier to gene flow between lake and sea habitat types cannot be due to dispersal limitation. We may thus have identified a case of rapid incipient speciation in post-glacial populations of a widespread aquatic plant.     

The Effects of Hydrostatic Pressure on Living Aquatic Organisms V. Eurybiotic Environmental Capacity as a Factor in High Pressure Tolerance

Study on the total spectrum of organisms (72 species) subjected to hydrostatic pressure as of this date allows one to established categories of pressure tolerance (resistance): Extremely high – eurybiotic forms (1000–1200 atm), High – marine littoral, planktonic, freshwater (600–1000 atm), Moderate – marine littoral, planktonic, freshwater (400–600 atm), Low – planktonic, freshwater (100–300 atm), Extremely low – planktonic, freshwater (0–100 atm). The average pressure tolerance of marine littoral species is higher than that of planktonic species but not significantly different from freshwater species. Eurybiotic species which are not marine seem to show the highest pressure tolerance.     

Impact of an invasive alga (Womersleyella setacea) on sponge assemblages: compromising the viability of future populations

The effects of invasive species on native fauna are understudied, even though their consequences should be taken into consideration for the proper conservation and management of marine systems. Furthermore, bioinvasions may have greater consequences if they affect key structural species with slow dynamics such as marine sponges. We propose that reproductive output could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species (i.e. sponges) as a result of biological invasions. The aim of this study was to investigate the effects of invasive algal (Womersleyella setacea) overgrowth on sponge reproduction by comparing the presence of reproductive elements (spermatic cysts, oocytes, embryos, and larvae) in sponges covered by a thick carpet of the invasive algae and in sponges dwelling in the same habitat but without the invasive algae. Three variables were calculated to assess the impact of the invasive alga on sponge reproduction: the reproductive effort, the proportion of individuals in reproduction, and the size of the reproductive structures. We studied eight sponge species representing the main components of the deep rocky reefs of the area. Our results showed that W. setacea had a strong negative effect on sponge reproduction in six out of eight sponge species studied, with lower and even nil reproductive structures on the sponges subjected to the algal overgrowth. Thus, considering that sexual reproduction is necessary for the persistence of most sponge populations, a significant and constant reduction of the reproductive effort may compromise their viability and affect future trends in these benthic systems.     

Phenotypic plasticity and priority rules for energy allocation in a freshwater clam: a field experiment

We studied resource allocation among maintenance, reproduction and growth in the freshwater clam Anodonta piscinalis. Recent theoretical and empirical studies imply that organisms with indeterminate growth may have priority rules for energy allocation. That being so, the traits involved should potentially be capable of considerable phenotypic modulation, as a mechanism to adjust allocation. We tested this hypothesis using a 1-year reciprocal transplant experiment at six sites. Experimental clams were caged at higher than natural densities in order to detect any phenotypic modulation of the traits and discover the putative priority rules in energy allocation. We recorded the survival and shell growth of clams during the experiment, and the reproductive output, somatic mass and fat content of clams at the end of the experiment. Shell growth, somatic mass, and the reproductive output of females varied more among transplant sites than among the populations of origin, suggesting a high capacity for phenotypic modulation. However, the reproductive investment, somatic mass and shell growth were also affected by origin; clams from productive habitats invested more in reproduction and were heavier. In comparison to undisturbed clams, the reproductive output of the experimental clams was similar and their fat content was higher, whereas their shell growth was considerably slower and their somatic mass lower. These results suggests that when resources are limiting (due to high density) reproductive allocation overrides allocation to somatic growth. The highest mortality during the experiment coincided with the period of reproductive stress in the spring. Additionally, the proportion of reproducing females was lower in those transplant groups where the survival rate was lowest, suggesting that maintenance allocation overrides allocation to reproduction when available resources are scarce. The results of this field experiment support theoretical predictions and results of previous laboratory experiments that suggest that there are priority rules for energy allocation in organisms with indeterminate growth.     

Life stage‐dependent effects of experimental heat waves on an insect herbivore

1. Worldwide concern about the consequences of climate change has prompted efforts to understand and predict the responses of populations to changes in temperature. 2. A heat wave can adversely affect organisms, may affect different life stages differently, and could decrease populations. In this study, green peach aphid [Myzus persicae (Sulzer)] nymphs, reproductive adults, and late‐reproductive adults were exposed to a heat wave, defined as 5 °C above the control temperature regime for five consecutive days. 3. The negative effects of experimental warming on development, reproduction, and survival negatively affected population growth. Nymphs and reproductive adults were more severely impacted than late‐reproductive adults. 4. Experiments designed to mimic temperature regimes can assess the direct effects of climate change on individuals and populations. Our study highlights the importance of assessing the life stage‐specific responses to heat stress.     

An empirical test of evolutionary theories for reproductive senescence and reproductive effort in the garter snake Thamnophis elegans

Evolutionary theory predicts that differential reproductive effort and rate of reproductive senescence will evolve under different rates of external mortality. We examine the evolutionary divergence of age-specific reproduction in two life-history ecotypes of the western terrestrial garter snake, Thamnophis elegans. We test for the signature of reproductive senescence (decreasing fecundity with age) and increasing reproductive effort with age (increasing reproductive productivity per gram female) in replicate populations of two life-history ecotypes: snakes that grow fast, mature young and have shorter lifespans, and snakes that grow slow, mature late and have long lives. The difference between life-history ecotypes is due to genetic divergence in growth rate. We find (i) reproductive success (live litter mass) increases with age in both ecotypes, but does so more rapidly in the fast-growth ecotype, (ii) reproductive failure increases with age in both ecotypes, but the proportion of reproductive failure to total reproductive output remains invariant, and (iii) reproductive effort remains constant in fast-growth individuals with age, but declines in slow-growth individuals. This illustration of increasing fecundity with age, even at the latest ages, deviates from standard expectations for reproductive senescence, as does the lack of increases in reproductive effort. We discuss our findings in light of recent theories regarding the phenomenon of increased reproduction throughout life in organisms with indeterminate growth and its potential to offset theoretical expectations for the ubiquity of senescence.     

A catchment‐scale perspective of plastic pollution

Plastic pollution is distributed across the globe, but compared with marine environments, there is only rudimentary understanding of the distribution and effects of plastics in other ecosystems. Here, we review the transport and effects of plastics across terrestrial, freshwater and marine environments. We focus on hydrological catchments as well‐defined landscape units that provide an integrating scale at which plastic pollution can be investigated and managed. Diverse processes are responsible for the observed ubiquity of plastic pollution, but sources, fluxes and sinks in river catchments are poorly quantified. Early indications are that rivers are hotspots of plastic pollution, supporting some of the highest recorded concentrations. River systems are also likely pivotal conduits for plastic transport among the terrestrial, floodplain, riparian, benthic and transitional ecosystems with which they connect. Although ecological effects of micro‐ and nanoplastics might arise through a variety of physical and chemical mechanisms, consensus and understanding of their nature, severity and scale are restricted. Furthermore, while individual‐level effects are often graphically represented in public media, knowledge of the extent and severity of the impacts of plastic at population, community and ecosystem levels is limited. Given the potential social, ecological and economic consequences, we call for more comprehensive investigations of plastic pollution in ecosystems to guide effective management action and risk assessment. This is reliant on (a) expanding research to quantify sources, sinks, fluxes and fates of plastics in catchments and transitional waters both independently as a major transport routes to marine ecosystems, (b) improving environmentally relevant dose–response relationships for different organisms and effect pathways, (c) scaling up from studies on individual organisms to populations and ecosystems, where individual effects are shown to cause harm and; (d) improving biomonitoring through developing ecologically relevant metrics based on contemporary plastic research.     

Infection with cowpox virus decreases female maturation rates in wild populations of woodland rodents

Sublethal effects of parasitic infection, such as reductions in reproductive rate, can significantly affect host population dynamics. Here we show that in wild populations of both Clethrionomys glareolus (bank vole) and Apodemus sylvaticus (wood mouse), females infected with cowpox virus are likely to delay maturation and therefore reproduction – in most cases until the following breeding season. Some infected bank voles do mature in their year of birth but still take longer than uninfected females. Together with our previous demonstration that individuals infected with cowpox virus in the summer survive better than uninfected individuals, these results support the prediction that hosts that develop an acute infection may best optimise their fitness by decreasing current reproduction to maximise the probability of surviving infection. Moreover, as the proportion of individuals infected increases with density, the reduction in host fecundity may have significant consequences for host dynamics.     

Physiological tipping points in the relationship between foraging success and lifetime fitness of a long-lived mammal

Although anthropogenic change is often gradual, the impacts on animal populations may be precipitous if physiological processes create tipping points between energy gain, reproduction or survival. We use 25 years of behavioural, diet and demographic data from elephant seals to characterise their relationships with lifetime fitness. Survival and reproduction increased with mass gain during long foraging trips preceding the pupping seasons, and there was a threshold where individuals that gained an additional 4.8% of their body mass (26 kg, from 206 to 232 kg) increased lifetime reproductive success three-fold (from 1.8 to 4.9 pups). This was due to a two-fold increase in pupping probability (30% to 76%) and a 7% increase in reproductive lifespan (6.0 to 6.4 years). The sharp threshold between mass gain and reproduction may explain reproductive failure observed in many species and demonstrates how small, gradual reductions in prey from anthropogenic disturbance could have profound implications for animal populations.