Life History Plasticity Research Articles

Facultative Adjustments in Future Planning Tendencies: Insights on Life History Plasticity from the Flint Water Crisis

Life history theory (LHT) is a powerful explanatory framework examining how developmental environments and life experiences shape allocations of effort to fitness-promoting domains in nested sets of trade-offs. Time orientation is a central psychological aspect of human life history variation, representing the degree to which behaviors are oriented towards immediate versus future goals. Identifying critical sensitive periods for shaping life history variation and verifying the scope of life history plasticity are important issues for both theory and practical application. Many LHT frameworks propose sensitive periods from gestational development through middle childhood, though recent research suggests facultative adjustments may occur much later in the lifespan. The current study examines how experiences of poor tap water quality during the Flint water crisis, associated with toxic contamination and adverse health effects, may have affected time orientations. Degraded expectations for health and longevity may have affected psychological aspects of life history variation, with important consequences for health-related behaviors. Controlling for socio-demographics and other environmental factors associated with life history variation, those who experienced worse tap water quality had lower general tendencies for future planning. Tap water quality experiences predicted several health-related behaviors, independent of socio-demographics, some relationships were mediated through tendencies for future planning.

Rapid changes in age and size at maturity in Lake Erie yellow perch (Perca flavescens) are not explained by harvest

Harvest can change phenotypic traits of populations through immediate demographic consequences, evolutionary responses to harvest selection, or developmental responses by individuals. This study investigated the plastic phenotypic effects of harvest on size and age at maturity in a commercially exploited freshwater fish. We tested an individual growth and life history plasticity model using lagged correlations incorporating how harvesting fish ages 2 and older influenced the abundance of juvenile fish, resource availability, individual growth rates, and carry-over responses in age and size at maturity. Our test used cohort data for Lake Erie yellow perch (Perca flavescens). Age and size at maturity fluctuated widely and rapidly across 23 cohorts between 1991 and 2013, suggesting phenotypic plasticity contributed strongly to maturation dynamics. The changes in maturity could not be explained by responses to harvest, as expected under the plasticity model. In Lake Erie, age and size at maturity in yellow perch appear to be responding to other drivers, such as harvest-induced dynamics of other fish stocks or ecosystem changes that are independent of harvest.

Spatiotemporal dynamics of mesocarnivore populations

Mammalian mesocarnivores play critical roles in ecosystems via trophic interactions. The fluctuation of mesocarnivore abundance may cause trophic cascading throughout the ecosystems. However, little was known about density dependence and spatiotemporal dynamics of mesocarnivore populations. Northern raccoon Procyon lotor is a common mammalian mesocarnivore in North America, and is the host of many human infectious diseases. Few studies have investigated density dependence and hierarchical spatiotemporal dynamics of raccoon populations. We used 23‐year time series of raccoon relative abundance from 14 wildlife management areas in Mississippi, USA, to test for spatial synchrony of raccoon populations with nonparametric correlation functions. We developed non‐Gaussian state space models to detect density dependence of raccoon populations, and also used dynamic factor analysis (DFA) to determine the structure of the spatiotemporal dynamics of raccoon populations. The 14 raccoon populations lacked common trends, and were not synchronized. Strength of density dependence varied among raccoon populations, but was not related to the amount of hardwood forests. Differences in the structure of density dependence probably prevented populations from being synchronize by climatic variability. The raccoon populations exhibited greater local or idiosyncratic variability than regional variability in Mississippi. Northern raccoons have plastic life history traits permitting their population dynamics to closely track local variations in resource availability.

Extreme Climate-Induced Life-History Plasticity in an Amphibian.

Age-specific survival and reproduction are closely linked to fitness and therefore subject to strong selection that typically limits their variability within species. Furthermore, adult survival rate in vertebrate populations is typically less variable over time than other life-history traits, such as fecundity or recruitment. Hence, adult survival is often conserved within a population over time, compared to the variation in survival found across taxa. In stark contrast to this general pattern, we report evidence of extreme short-term variation of adult survival in Rose's mountain toadlet (Capensibufo rosei), which is apparently climate induced. Over 7 years, annual survival rate varied between 0.04 and 0.92, and 94% of this variation was explained by variation in breeding-season rainfall. Preliminary results suggest that this variation reflects adaptive life-history plasticity to a degree thus far unrecorded for any vertebrate, rather than direct rainfall-induced mortality. In wet years, these toads appeared to achieve increased reproduction at the expense of their own survival, whereas in dry years, their survival increased at the expense of reproduction. Such environmentally induced plasticity may reflect a diversity of life-history strategies not previously appreciated among vertebrates.

Both life-history plasticity and local adaptation will shape range-wide responses to climate warming in the tundra plant Silene acaulis.

Many predictions of how climate change will impact biodiversity have focused on range shifts using species-wide climate tolerances, an approach that ignores the demographic mechanisms that enable species to attain broad geographic distributions. But these mechanisms matter, as responses to climate change could fundamentally differ depending on the contributions of life-history plasticity vs. local adaptation to species-wide climate tolerances. In particular, if local adaptation to climate is strong, populations across a species' range-not only those at the trailing range edge-could decline sharply with global climate change. Indeed, faster rates of climate change in many high latitude regions could combine with local adaptation to generate sharper declines well away from trailing edges. Combining 15years of demographic data from field populations across North America with growth chamber warming experiments, we show that growth and survival in a widespread tundra plant show compensatory responses to warming throughout the species' latitudinal range, buffering overall performance across a range of temperatures. However, populations also differ in their temperature responses, consistent with adaptation to local climate, especially growing season temperature. In particular, warming begins to negatively impact plant growth at cooler temperatures for plants from colder, northern populations than for those from warmer, southern populations, both in the field and in growth chambers. Furthermore, the individuals and maternal families with the fastest growth also have the lowest water use efficiency at all temperatures, suggesting that a trade-off between growth and water use efficiency could further constrain responses to forecasted warming and drying. Taken together, these results suggest that populations throughout species' ranges could be at risk of decline with continued climate change, and that the focus on trailing edge populations risks overlooking the largest potential impacts of climate change on species' abundance and distribution.

Physiological and Life-History Plasticity in a Harvestman Species: Contrasting Laboratory with Field Data

Phenotypic plasticity is defined as the ability of an organism to produce different phenotypes in response to changes in internal or external environmental conditions. Experimental modification of animal diets has been widely used to study phenotypic plasticity in physiological and life-history traits. Here we compared the data from a previous experiment, conducted in a harvestman species, that was aimed to evaluate the effect of diet quality on maintenance costs (standard metabolic rate), growth rate, internal organ size (visceral mass) and fecundity (clutch mass and egg number), with new data obtained from field (mark—recapture) specimens. We assumed that of the two experimental diets tested before, animals in the field would probably consume the one of intermediate quality (i.e. have a generalist omnivorous diet), and then, we predicted that field animals should exhibit intermediate values for both physiological and life-history traits. We found that field animals and animals consuming a high quality diet showed a greater growth rate than animals consuming a poor quality diet. In addition, animals consuming a high quality diet showed a larger clutch mass than both field animals and animals consuming a poor quality diet, which, in turn, was related to higher maintenance costs. Our results illustrate how animals adopt different life history strategies according to the quality of the diet that is available, which is correlated with phenotypic adjustments at the anatomical and physiological levels.

Use of Morphological and Physiological Indices to Characterize Life History Diversity in Juvenile Hatchery Winter‐Run Steelhead

AbstractSteelhead Oncorhynchus mykiss exhibit significant life history plasticity, including variation in freshwater residence time, age of smoltification, and maturation that are influenced by exceeding specific thresholds in size or body energy stores. Fish that do not reach minimum thresholds for smoltification or exceed thresholds for maturation may “residualize” in freshwater. Understanding life history diversity is important in steelhead hatchery programs. The objective of this investigation was to characterize life history diversity in Hood River, Oregon, hatchery winter‐run steelhead prior to release. We used both morphological and physiological indices to assess degree of smoltification in both sexes and maturation in males. Smoltification was categorized by measuring size, visual smolt index, and gill Na+/K+‐ATPase activity. All females were determined to be immature. Male reproductive development required histological staging of testes. Other indices of maturation—including gonadosomatic index, plasma 11‐ketotestosterone, and pituitary fshb and lhb and testis ifg3 and amh gene expression—were also employed, with varying degrees of success. Five phenotypes were described: (1) immature male and female parr; (2) precociously mature male parr; (3) male smolts in early to mid‐spermatogenesis that are likely to spawn after <1 year in the ocean; (4) males that might have attempted maturation, but failed; and (5) immature male and female smolts that could mature after >1 year in the ocean. Over three brood years, we estimated that 3–4% of the population could potentially residualize due to failure to smolt or precocious male maturation, 1–12% could mature after <1 year in the ocean (one salt male), and 84–95% could mature after >1 year in the ocean (two to three salt males and females). Based on previous studies conducted in the Hood River basin, the residualism rate estimated for this hatchery population is lower than that of naturally rearing Hood River steelhead.Received November 2, 2016; accepted February 14, 2017 Published online May 11, 2017

Evidence for Freshwater Residualism in Coho Salmon, <i>Oncorhynchus kisutch</i>, From a Watershed on the North Coast of British Columbia

The Coho Salmon, Oncorhynchus kisutch, is one of seven species of Pacific salmon and trout native to northeastern Pacific Ocean watersheds. The species is typically anadromous; adults reproduce in fresh water where juveniles reside for 1–2 years before seaward migration after which the majority of growth occurs in the ocean before maturation at 2–4 years old when adults return to fresh water to spawn. Here, we report maturation of Coho Salmon in two freshwater lakes on the north coast of British Columbia apparently without their being to sea. A total of 15 mature fish (11 males and four females) were collected in two lakes across two years. The mature fish were all at least 29 cm in total length and ranged in age from three to five years old. The occurrence of Coho Salmon that have matured in fresh water without first going to sea is exceedingly rare in their natural range, especially for females. Such mature Coho Salmon may represent residual and distinct breeding populations from those in adjacent streams. Alternatively, they may result from the ephemeral restriction in the opportunity to migrate seaward owing to low water levels in the spring when Coho Salmon typically migrate to sea after 1–2 years in fresh water. Regardless of their origin, the ability to mature in fresh water without seaward migration may represent important adaptive life history plasticity in response to variable environments.

Life history trade-offs, the intensity of competition, and coexistence in novel and evolving communities under climate change.

The consequences of climate change for local biodiversity are little understood in process or mechanism, but these changes are likely to reflect both changing regional species pools and changing competitive interactions. Previous empirical work largely supports the idea that competition will intensify under climate change, promoting competitive exclusions and local extinctions, while theory and conceptual work indicate that relaxed competition may in fact buffer communities from biodiversity losses that are typically witnessed at broader spatial scales. In this review, we apply life history theory to understand the conditions under which these alternative scenarios may play out in the context of a range-shifting biota undergoing rapid evolutionary and environmental change, and at both leading-edge and trailing-edge communities. We conclude that, in general, warming temperatures are likely to reduce life history variation among competitors, intensifying competition in both established and novel communities. However, longer growing seasons, severe environmental stress and increased climatic variability associated with climate change may buffer these communities against intensified competition. The role of life history plasticity and evolution has been previously underappreciated in community ecology, but may hold the key to understanding changing species interactions and local biodiversity under changing climates.This article is part of the themed issue 'Human influences on evolution, and the ecological and societal consequences'.

Life history plasticity does not confer resilience to environmental change in the mole salamander (Ambystoma talpoideum).

Plasticity in life history strategies can be advantageous for species that occupy spatially or temporally variable environments. We examined how phenotypic plasticity influences responses of the mole salamander, Ambystoma talpoideum, to disturbance events at the St. Marks National Wildlife Refuge (SMNWR), FL, USA from 2009 to 2014. We observed periods of extensive drought early in the study, in contrast to high rainfall and expansive flooding events in later years. Flooding facilitated colonization of predatory fishes to isolated wetlands across the refuge. We employed multistate occupancy models to determine how this natural experiment influenced the occurrence of aquatic larvae and paedomorphic adults and what implications this may have for the population. We found that, in terms of occurrence, responses to environmental variation differed between larvae and paedomorphs, but plasticity (i.e. the ability to metamorphose rather than remain in aquatic environment) was not sufficient to buffer populations from declining as a result of environmental perturbations. Drought and fish presence negatively influenced occurrence dynamics of larval and paedomorphic mole salamanders and, consequently, contributed to observed short-term declines of this species. Overall occurrence of larval salamanders decreased from 0.611 in 2009 to 0.075 in 2014 and paedomorph occurrence decreased from 0.311 in 2009 to 0.121 in 2014. Although variation in selection pressures has likely maintained this polyphenism previously, our results suggest that continued changes in environmental variability and the persistence of fish in isolated wetlands could lead to a loss of paedomorphosis in the SMNWR population and, ultimately, impact regional persistence in the future.

Life-history plasticity in amphidromous and catadromous fishes: a continuum of strategies

Plastic life-history strategies in diadromous fishes have long been acknowledged but have often been viewed as anomalies. Until recently, techniques were lacking to investigate the prevalence and variety of life-history strategies. However, recent technical advances, such as otolith trace element and stable isotope analyses, have provided insights into the life-histories of migratory fish, often revealing considerable plasticity. Reviews of anadromy and catadromy examined the extent of plasticity in these life-histories; however amphidromy has not been reviewed. Amphidromy, the most widespread diadromous life-history (273 + sp.), consists of two types: freshwater amphidromy, where fish rear in the ocean as larvae and return to freshwater as juveniles for growth and reproduction, and marine amphidromy, where fish utilize the marine environment for larval growth, enter freshwater for a short time, and return to the marine environment for further growth and spawning. In this review, a detailed taxonomic examination of plasticity in amphidromous fishes is utilized to determine its prevalence and ecological role. Our results indicate plasticity, as evidenced by variable use of fresh or marine environments for key life-history stages, is present on both evolutionary and ecological scales in most families of amphidromous fishes. Such variability indicates amphidromy is not necessarily a diadromous migration, but is better viewed as a spatially extensive benthic-pelagic migration. Further, adult downstream migration by amphidromous fishes parallels catadromy, suggesting a life-history continuum linking fluvial, amphidromous, catadromous, and oceanadromous life-histories. The role of egg-size/fecundity tradeoffs, migration, salinity, and landscape are discussed in the context of benthic-pelagic centered life-histories.

A Meta-Analysis on Facultative Responses of Embryonic Amphibians to Predation Risk

Natural selection is predicted to favor the evolution of life history plasticity in response to differences in mortality risk between life stages, such that the duration of the more dangerous stage is reduced. I report a meta-analysis of 29 published tests of this hypothesis involving 20 amphibian species, in which exposure of embryos to predation risk was experimentally manipulated. The results confirm that amphibians are sensitive to risk during the embryonic stage, but the predictions of theory were only weakly upheld. Amphibians hatch at a less advanced developmental stage (0.24 SD units) and smaller body size (0.10 SD units) when exposed to predator species that consume eggs, but the expected decline in age at hatching (0.16 SD units) was not significant. Predators that consume larvae did not significantly delay hatching (0.19 SD units) or influence any other response.

Environmental effects on the jumbo squid fishery along Baja California’s west coast

Since 2000, jumbo squid Dosidicus gigas catches in Baja California have increased steadily with a record catch in 2011 of 14,243,689 kg. However, little is known about stock size, distribution and seasonality, as well as the possible effects of the environment on the fishery. We tested D. gigas catches (CPUE) from 2006 to 2013 with Pacific sardine Sardinops caeruleus fishery catch data, as well as the primary productivity anomaly, sea surface temperature anomaly (SSTa), Multivariate El Nino Index (MEI), North Pacific Gyre Oscillation Index (NPGO), and price/kg using a general linear model. We also estimated D. gigas population size using two depletion models. More than 80 % of D. gigas captures for 2006–2013 occurred within 20 nmi from the coast, regardless of the fleet. We identified Salsipuedes, Soledad Bay and Vizcaino Bay as the most important D. gigas fishing grounds. D. gigas CPUE showed monthly differences, with July and August being significantly different from other months (p < 0.041; and p < 0.006, respectively). S. caeruleus and D. gigas fishing grounds overlapped geographically more than 75 %; however no correlation between catch volumes was found (p < 0.562). There was an inverse linear and significant relation between D. gigas monthly catches and the primary productivity anomaly (p < 0.021) and price/kg (p < 0.016), where a positive primary productivity anomaly and price/kg values yielded a D. gigas CPUE below 9 × 103 kg. We did not find any direct relation between SSTa, MEI, NPGO and D. gigas catches (p < 0.785; p < 0.497; and p < 0.108, respectiveley). Lack of independent fisheries data, as well as thermal tolerance and plastic life history of D. gigas, may provide an explanation on the non-apparent effect of biotical and abiotical factors in the relative abundance of D. gigas along Baja California’s west coast.

A Photoreceptor Contributes to the Natural Variation of Diapause Induction in Daphnia magna.

Diapause is an adaptation that allows organisms to survive harsh environmental conditions. In species occurring over broad habitat ranges, both the timing and the intensity of diapause induction can vary across populations, revealing patterns of local adaptation. Understanding the genetic architecture of this fitness-related trait would help clarify how populations adapt to their local environments. In the cyclical parthenogenetic crustacean Daphnia magna, diapause induction is a phenotypic plastic life history trait linked to sexual reproduction, as asexual females have the ability to switch to sexual reproduction and produce resting stages, their sole strategy for surviving habitat deterioration. We have previously shown that the induction of resting stage production correlates with changes in photoperiod that indicate the imminence of habitat deterioration and have identified a Quantitative Trait Locus (QTL) responsible for some of the variation in the induction of resting stages. Here, new data allows us to anchor the QTL to a large scaffold and then, using a combination of a new mapping panel, targeted association mapping and selection analysis in natural populations, to identify candidate genes within the QTL. Our results show that variation in a rhodopsin photoreceptor gene plays a significant role in the variation observed in resting stage induction. This finding provides a mechanistic explanation for the link between diapause and day-length perception that has been suggested in diverse arthropod taxa.

A review of growth and life-history traits of native and non-native European populations of black bullhead Ameiurus melas

North American black bullhead, Ameiurus melas, which were introduced to Europe in the nineteenth and twentieth centuries, have received relatively little study. With focus on growth and reproduction, this extensive review, which includes new European data, aims to inform the risk analysis process concerning this non-native species in Europe. Surprisingly, the new data for Europe were more comprehensive than for native populations, with data available mainly from Oklahoma, and North and South Dakota (USA). In terms of relative growth, juvenile A. melas were found to have a relatively uniform body shape regardless of the population’s origin, whereas adults developed different phenotypes depending upon location. Overall growth trajectory was significantly faster for native than for non-native populations. Growth index values decreased significantly with increasing latitude in non-native but not native populations—the latter decreasing weakly with increasing altitude in the populations located at latitudes <40°. Mean general condition (slope ‘b’), mean sex ratio and mean egg diameter did not differ significantly between native and non-native populations. Absolute fecundity was slightly (but not significantly) higher in non-native than native populations. GSI data, which were very scarce for native populations, suggest gonad production may be slightly higher in native than in non-native populations. Precise data on age at maturity (AaM) are lacking for the native range, where 2–5 years is reported. Whereas, in the introduced range the greatest AaM was 3.5 years, and AaM decreases with increasing juvenile growth (TL at age 3). The populations with fastest juvenile growth tended to be from warmer water bodies where they are considered to be invasive. The great growth and life-history plasticity of black bullhead affords the species great potential to invade and establish viable populations in new areas.

Contributions of dynamic environmental signals during life-cycle transitions to early life-history traits in lodgepole pine (&amp;lt;i&amp;gt;Pinus contorta&amp;lt;/i&amp;gt; Dougl.)

Abstract. Environmental signals are important triggers in the life-cycle transitions and play a crucial role in the life-history evolution. Yet very little is known about the leading ecological factors contributing to the variations of life-history traits in perennial plants. This paper explores both the causes and consequences for the evolution of life-history traits (i.e., seed dormancy and size) in lodgepole pine (Pinus contorta Dougl.) across British Columbia (B.C.), Canada. We selected 83 logepole pine populations covering 22 ecosystem zones of B.C. and through their geographic coordinate, 197 climatic variables were generated accordingly for the reference (1961–1990) and future (2041–2070) periods. We found that dynamic climatic variables rather than constant geographic variables are the true environmental driving forces in seed dormancy and size variations and thus provide reliable predictors in response to global climate change. Evapotranspiration and precipitation in the plant-to-seed chronology are the most critical climate variables for seed dormancy and size variations, respectively. Hence, we predicted that levels of seed dormancy in lodgepole pine would increase across large tracts of B.C. in 2050s. Winter-chilling is able to increase the magnitude of life-history plasticity and lower the bet-hedge strategy in the seed-to-plant transition; however, winter-chilling is likely to be insufficient in the north of 49° N in 2050s, which may delay germination while unfavorable conditions during dry summers may result in adverse consequences in the survival of seedlings owing to extended germination span. These findings provide useful information to studies related to assessments of seed transfer and tree adaptation.

Fish life history dynamics: shifts in prey size structure evoke shifts in predator maturation traits

A bioenergetic framework is developed to predict optimal life history responses to environmentally driven changes in the rate of energy production by a predator. This framework is used to predict the responses of age at maturation, size at maturation, and asymptotic size to changes in the predator–prey size ratio. Predators feeding on relatively smaller prey (i.e., having larger predator–prey size ratios) have lower growth efficiency and are predicted as a consequence to mature earlier, at smaller sizes, and reach smaller asymptotic sizes. This prediction was tested using a 78-year time series (1936–2013) of data from a natural population of lake trout (Salvelinus namaycush) in Lake Opeongo, Algonquin Park, Ontario, Canada. A large decrease in the predator–prey size ratio for this population occurred over the period 1950–1965 when a preferred prey (cisco, Coregonus artedii) was introduced to the lake. This decrease was followed by ∼20 years of constancy in the size ratio and then 25 years of progressive increase. Lake trout life history responded plastically during both periods and consistently with our predictions. Extensive analysis of available data provided little empirical support for alternative explanations for the observed changes in lake trout size and maturity (e.g., changes in cisco and (or) lake trout density and harvest rates). The framework developed here derives plastic life history changes from fixed developmental thresholds that are based on the scaling of net production with body size and can be used to predict the shape of maturation reaction norms for the major shifts in community structure that are compactly summarized by changes in size spectrum parameters.

Effects of food availability on growth and reproduction of the deep-sea pedunculate barnacle Heteralepas canci

Sessile animals living on continental shelves or slopes may adjust their growth and reproduction according to temporally and spatially variable food availability, but little information is available on these animals to date. We collected the pedunculate barnacle Heteralepas canci on a continental slope at a depth of 229m off Cape Nomamisaki in southern Japan. We developed a rearing method for the barnacles and studied their growth and reproduction at different food levels in the laboratory. A total of 136 individual H. canci were fed with Artemia salina larvae and brewer's yeast at three different food levels for 100 days. Both the growth and the ovary development were delayed when food availability was low, whereas the survival rate was lower at the high food level. In addition, an individual survived under complete starvation for 167 days. We concluded that H. canci has plastic life history traits that are adaptive for variable food availability.

A benign juvenile environment reduces the strength of antagonistic pleiotropy and genetic variation in the rate of senescence.

Summary The environment can play an important role in the evolution of senescence because the optimal allocation between somatic maintenance and reproduction depends on external factors influencing life expectancy.The aims of this study were to experimentally test whether environmental conditions during early life can shape senescence schedules, and if so, to examine whether variation among individuals or genotypes with respect to the degree of ageing differs across environments.We tested life‐history plasticity and quantified genetic effects on the pattern of senescence across different environments within a reaction norm framework by using an experiment on the three‐spined stickleback (Gasterosteus aculeatus, Linnaeus) in which F1 families originating from a wild annual population experienced different temperature regimes.Male sticklebacks that had experienced a more benign environment earlier in life subsequently reduced their investment in carotenoid‐based sexual signals early in the breeding season, and consequently senesced at a slower rate later in the season, compared to those that had developed under harsher conditions. This plasticity of ageing was genetically determined. Both antagonistic pleiotropy and genetic variation in the rate of senescence were evident only in the individuals raised in the harsher environment.The experimental demonstration of genotype‐by‐environment interactions influencing the rate of reproductive senescence provides interesting insights into the role of the environment in the evolution of life histories. The results suggest that benign conditions weaken the scope for senescence to evolve and that the dependence on the environment may maintain genetic variation under selection.

Population Variation in the Life History of a Land Fish, Alticus arnoldorum, and the Effects of Predation and Density.

Life history variation can often reflect differences in age-specific mortality within populations, with the general expectation that reproduction should be shifted away from ages experiencing increased mortality. Investigators of life history in vertebrates frequently focus on the impact of predation, but there is increasing evidence that predation may have unexpected impacts on population density that in turn prompt unexpected changes in life history. There are also other reasons why density might impact life history independently of predation or mortality more generally. We investigated the consequences of predation and density on life history variation among populations of the Pacific leaping blenny, Alticus arnoldorum. This fish from the island of Guam spends its adult life out of the water on rocks in the splash zone, where it is vulnerable to predation and can be expected to be sensitive to changes in population density that impact resource availability. We found populations invested more in reproduction as predation decreased, while growth rate varied primarily in response to population density. These differences in life history among populations are likely plastic given the extensive gene flow among populations revealed by a previous study. The influence of predation and density on life history was unlikely to have operated independently of each other, with predation rate tending to be associated with reduced population densities. Taken together, our results suggest predation and density can have complex influences on life history, and that plastic life history traits could allow populations to persist in new or rapidly changing environments.