Life History Forms Research Articles

Life strategies of pacific salmon. Communication 2. Formation of life-history forms. Variability in sex ratio

Conditions determining the vector of ontogenetic development and factors influencing the sex ratio for various life-history forms of pacific salmon (gen. Oncorhynchus) are discussed on the basis of cited data.

Differences in life history patterns of American shad (Alosa sapi dissima) populations between ancestral, Atlantic coast, and non-native Pacific coast rivers of North America

Organisms naturalized outside their native range can reveal new life history patterns in new environments. Here, we compare life history patterns of American shad, Alosa sapidissima, from five rivers along the U.S. Pacific coast (introduced range) with contemporary data from the Atlantic coast source populations. The Pacific coast fish grew slower, matured at a younger age, and were less often iteroparous than conspecifics from the Hudson River and Susquehanna River sources. Differences among the Pacific coast populations indicated that some combination of phenotypic plasticity and genetic adaptation has occurred since the transplants in the 1870s. Microchemical analysis of otoliths from returning adults demonstrated an immature, extended freshwater life history form, locally known as “mini-shad”. These fish remain in the river for at least 1 year or enter salt water briefly and then return to fresh water for several months prior to subsequent seaward migration and return as adults. This and other forms of variation (extent of estuary use and size at sea water entry) expand the understanding of Alosine migration and life history diversity.

Using riverscape genetics to investigate the genetic response of two species and their life-history forms to dam removal

Barriers such as hydroelectric dams inhibit migratory pathways essential to many aquatic species, resulting in significant losses of species, their unique life-history forms, and genetic diversity. Understanding the impacts of dam removal to species recovery at these different biological levels is crucial to fully understand the restoration response. We used the removal of two large dams on the Elwha River as an opportunity to characterize how restored connectivity impacts the reestablishment of two fish species, Chinook salmon (Oncorhynchus tshawytscha) and Steelhead/rainbow trout (Oncorhynchus mykiss), and their unique ocean migration return-timing life-history forms. In this study, we employed riverscape genetics to understand how restoration and the environment influence the distribution of neutral and return-timing genetic variation underlying the migratory life-history forms and species at- and between- sampling sites. We genotyped fish sampled over time and space in the Elwha River using Genotyping-in-Thousands by sequencing (GTseq) loci for both species at neutral and putatively adaptive loci in and near the major effect genic region GREB1L/ROCK1 putatively associated with migration timing. We observed little evidence of genetic structure for either species, but a statistically significant increase in early return-timing alleles in upriver O. mykiss population post-dam removal. For O. tshawytscha, at-site genetic variation was shaped by river distance and a combination of environmental habitat differences, while between-site genetic variation was mainly shaped by river distance. For all O. mykiss, at- and between-site genetic variation is primarily explained by river distance. Genetic variation in juvenile and adult Steelhead, respectively, were influenced by at- and between-site environmental and habitat differences. Our study illustrates the power of using genetics to understand the implications of both demography and environment in facilitating the recovery of species and their diverse life-history forms following barrier removal.

Using social-ecological models to explore stream connectivity outcomes for stakeholders and Yellowstone cutthroat trout.

Despite growing interest in conservation and re-establishment of ecological connectivity, few studies have explored its context-specific social-ecological outcomes. We aimed to explore social and ecological outcomes to changing stream connectivity for both stakeholders and native fish species impacted by habitat fragmentation and nonnative species. We (1) investigated stakeholder perceptions of the drivers and outcomes of stream connectivity, and (2) evaluated the effects of stakeholder-identified connectivity and nonnative species scenarios on Yellowstone cutthroat trout (YCT) populations. Our study was conducted in the Teton River, Idaho, USA. We integrated two modeling approaches, mental modeling and individual-based ecological modeling, to explore social-ecological outcomes for stakeholders and YCT populations. Aggregation of mental models revealed an emergent pattern of increasing complexity as more types of stakeholders were considered, as well as gaps and linkages among different stakeholder knowledge areas. These results highlight the importance of knowledge sharing among stakeholders when making decisions about connectivity. Additionally, the results from the individual-based models suggested that the potential for a large, migratory life history form of YCT, in addition to self-preference mating where they overlap with rainbow trout, had the strongest effects on outcomes for YCT. Exploring social and ecological drivers and outcomes to changing connectivity is useful for anticipating and adapting to unintended outcomes, as well as making decisions for desirable outcomes. The results from this study can contribute to the management dialogue surrounding stream connectivity in the Teton River, as well as to our understanding of connectivity conservation and its outcomes more broadly.

Sources of coaster brook trout (Salvelinus fontinalis) revealed by genomic analysis of brook trout populations along Minnesota’s shoreline with Lake Superior

Knowledge of population-level relationships and how these relationships pertain to different life history forms is critical to developing effective management plans for native trout, char, and salmon. In the Lake Superior basin, identifying effective restoration strategies for coaster brook trout (Salvelinus fontinalis), a lake-inhabiting form of brook trout, is hampered by limited information on genetic connectivity and source-sink dynamics among brook trout populations. Here, we infer these relationships by surveying 8,178 single nucleotide polymorphisms in 234 brook trout from seven rivers along the Minnesota shoreline with Lake Superior, including from reaches above and below natural waterfalls that prevent upstream movement. We identified well-differentiated above-barrier populations that supply brook trout to below-barrier reaches. We also compared within-river brook trout to 26 coaster brook trout from Lake Superior. We identified at least four source populations for these coaster brook trout, three of which were located within rivers. Additionally, we estimated NE for within-river populations and detected a decline across recent generations, with the most recent estimates approaching critical thresholds. Finally, comparisons with 94 domestic brook trout representing nine hatchery strains revealed a lack of domestic introgression into wild populations, demonstrating the importance of natural reproduction to population persistence. Our results offer novel insights into sources of coaster brook trout and highlight the role of within-river populations in supporting the coaster life history. Management efforts focused on instream restoration may be more important to rehabilitating coaster brook trout than previously thought and are urgently needed given the population-level conservation status reported here.

Vital rates of a burgeoning population of Humpback Chub in western Grand Canyon

AbstractObjectiveThe Colorado River ecosystem has experienced habitat alterations and nonnative species invasions; as a result, many of its native species have had extirpations, abundance declines, and range constrictions. Despite these pitfalls, the Humpback Chub Gila cypha has persisted and in the last 10–15 years has expanded its range to become abundant in western Grand Canyon, a river segment in which it had been rare for the prior three decades. The goal of this study was to evaluate the population dynamics (i.e., growth, survival, movement, abundance) for this “new” group of Humpback Chub.MethodsWe analyzed a 6‐year mark–recapture study from a fixed monitoring reach in western Grand Canyon, and we provide the first estimates of survival and growth (vital rates) for these fish. We compared vital rates in western Grand Canyon to those of two life history forms (residents and migrants, representing fast and slow life history trajectories, respectively) from the more established Little Colorado River (LCR) aggregation in eastern Grand Canyon.ResultCompared to LCR migrants and LCR residents, Humpback Chub in western Grand Canyon had intermediate values for apparent survival, growth, and asymptotic length. Relatively high survival of subadults coupled with fast growth allowed for rapid population growth in western Grand Canyon. However, a large cohort in 2017 failed to lead to noticeable increases in adults. Seasonal survival patterns were distinct in all three groups, and apparent survival was lowest in western Grand Canyon during spring months. Adult Humpback Chub in western Grand Canyon were mobile and had a high probability of transience (i.e., just passing through the reach) and temporary emigration, demonstrating the need for future movement studies in western Grand Canyon to better distinguish emigration from survival.ConclusionThere is considerable spatial variability in viral rates for Humpback Chub in Grand Canyon. We discuss how observations are related to disparate temperature regimes experienced by the three groups and whether (how) the relationship between metabolism and temperature influences vital rates within the river network.

Otolith 87Sr/86Sr identifies natal origin, movement and life history of Burbot Lota lota in the Kootenai River following 45 years of impoundment

AbstractHydropower has long been an effective form of renewable energy, but the development of the resource has negatively impacted fishes throughout the world. Formulating recovery plans to mitigate these effects requires a firm understanding of species‐specific provenance, life history and life stage habitat requirements. However, the importance of this information is often only recognised after a substantial population decline, when obtaining it becomes demographically challenging. We provide a case study for this scenario and present a post hoc approach to gain insight into these critical data gaps for Burbot Lota lota in the upper Kootenai River in Montana and British Columbia. The population once supported a robust tribal and recreational harvest but declined following impoundment and these fisheries have remained closed or curtailed for nearly 20 years. The reasons for the decline are unknown and actions to assist recovery have been constrained by limited information regarding natal origin, life history and habitat use. We addressed this issue using strontium isotope ratios (87Sr/86Sr) in otoliths collected over four decades in Lake Koocanusa, the reservoir on the Kootenai River above Libby Dam. Due to the geologic heterogeneity of the basin and resulting variation in water 87Sr/86Sr, the assignment probability for Burbot to their region of natal origin approached unity. Otolith 87Sr/86Sr also indicated the population was comprised of mainstem‐ and tributary‐origin forms and their relative abundance changed over time. Mainstem Burbot was most abundant during the 1970s and 2000s, whereas tributary forms dominated between these periods. We suggest ecosystem changes following impoundment contributed to this shift in life history forms and the overall decline of the population. Our findings underscore the need for additional investigations of these impacts to guide restoration efforts.

Rapid Colonization of Upstream Habitats by Oncorhynchus Mykiss Following Culvert Modification

AbstractHabitat fragmentation threatens the persistence of fish populations, and road crossings (e.g., culverts) are particularly problematic because they are globally ubiquitous and can block access to critical habitats. Barrier removal or modifications that allow upstream access can result in expanded distributions, increased abundances, and gene flow among historically isolated populations. Actions that promote connectivity, gene flow, and the potential expression of multiple life history forms (e.g., anadromy in Pacific salmon Oncorhynchus spp.) are thought to buffer against extinction and are increasingly important given the high rates of imperilment for many fish species. We collected genetic samples from juvenile O. mykiss (anadromous steelhead and resident Rainbow Trout) prior to and following the modification of a culvert that served as a historical barrier to upstream movement and tested for changes in genetic composition through time. Prior to culvert modification, levels of genetic diversity were low and genetic differentiation with reference collections of anadromous steelhead was high. After treatment, we observed increased levels of genetic diversity, larger estimates of effective population size, and decreased genetic differentiation with steelhead, indicating an influx of individuals from a downstream population. Using an inexpensive genetic‐based monitoring approach, we show that culvert modification can result in the rapid reestablishment of connectivity between historically isolated populations.

Effect of paternal life-history form and egg size on offspring life-history traits in masu salmon Oncorhynchus masou

Effect of paternal life-history form and egg size on offspring life-history traits in masu salmon Oncorhynchus masou

Systematic affinities of Zygophylacidae (Cnidaria: Hydrozoa: Macrocolonia) with descriptions of 15 deep-sea species

AbstractHydrozoans (Cnidaria) are distributed worldwide and exhibit alternating benthic polyp (hydroid) and pelagic medusan life-history forms. Zygophylacidae are a hydrozoan family with an exclusive hydroid stage throughout their life cycle. Within Hydrozoa, they are unusual in that a relatively large proportion (50%) of species occur in deep waters, but their validity and systematic affinities have been controversial for more than a century. Here, 97 deep-sea specimens, collected by manned submersible or bottom dredging, were investigated using an integrative taxonomical approach. Molecular data concatenating the 16S, 18S and 28S rRNA genes support the validity of Zygophylacidae and their placement within Macrocolonia, instead of Lafoeida. Fourteen zygophylacids and one relevant lafoeid are described or re-described, including three newly proposed species: Zygophylax lighti sp. nov. and Z. tankahkeei sp. nov. from the South China Sea, Z. pseudosibogae sp. nov. from Portugal and five species introduced by Eberhard Stechow (1883–1959) through the re-examination of type material. Four candidate generic diagnoses are discussed for future Zygophylacidae fine systematics by integrating a taxonomic review of all 74 zygophylacids. Morphological characters such as long hydrothecae and complex protective gonothecal structures mostly present in the deep-sea zygophylacids are heuristic for future functional morphology and evolutionary studies.

Does fragmented river connectivity alter the reproductive behavior of the potamodromous fish Alburnus vistonicus?

Blocked riverine spawning migration routes constitute one of the main threats of potamodromous fish that require well-connected habitats of high quality to maintain their unique life-history form. Alburnus vistonicus, a potamodromous species inhabiting the Vistonis freshwater system in northern Greece, manages to cope with wide salinity fluctuations in Vistonis Lake, but the impact of the fragmented connectivity of the lake’s two main freshwater suppliers, Kosynthos and Kompsatos rivers, has not been assessed. We analyzed the species whole reproductive cycle and we divided it into phases. Cyclicity was observed in gonadosomatic index and oocyte diameter, while total fecundity remained constant prior to the onset of the spawning season. Stomach fullness and condition factor differed among the surveyed habitats. Successful spawning and multiple spawning were verified, as well as spawning migration and potamodromy. However, mature females with markers of recent spawning activity were captured also in the lake, suggesting spawning occurrence in the lake or a previously undocumented oscillatory behavior between the lake and the rivers during the spawning season and between sequential spawning events. Either behavior may serve as a mechanism to overcome the restricted spawning migration routes due to the fragmented river connectivity.

Evolutionary history and ecology shape the diversity and abundance of phytochemical arsenals across monkeyflowers.

We examine the extent to which phylogenetic effects and ecology are associated with macroevolutionary patterns of phytochemical defence production across the Mimulus phylogeny. We grew plants from 21 species representing the five major sections of the Mimulus phylogeny in a common garden to assess how the arsenals (NMDS groupings) and abundances (concentrations) of a phytochemical defence, phenylpropanoid glycosides (PPGs), vary across the phylogeny. Very few PPGs are widespread across the genus, but many are common to multiple sections of the genus. Phytochemical arsenals cluster among sections in an NMDS and are not associated with total concentration of PPGs. There is a strong phylogenetic signal for phytochemical arsenal composition across the Mimulus genus, whereas ecological variables such as growing season length, latitude, and elevation do not significantly influence arsenal. In contrast, there is little phylogenetic signal for total PPG concentration, and this trait is significantly influenced by several ecological factors. Phytochemical arsenals and abundances are influenced by plant life history form. Both phylogenetic effects and ecology are related to phytochemical patterns across species, albeit in different ways. The independence of phytochemical defence concentrations from arsenal compositions indicates that these aspects of defence may continue to evolve independently of one another.

The Impacts of Dam Construction and Removal on the Genetics of Recovering Steelhead (Oncorhynchus mykiss) Populations across the Elwha River Watershed

Dam construction and longitudinal river habitat fragmentation disrupt important life histories and movement of aquatic species. This is especially true for Oncorhynchus mykiss that exhibits both migratory (steelhead) and non-migratory (resident rainbow) forms. While the negative effects of dams on salmonids have been extensively documented, few studies have had the opportunity to compare population genetic diversity and structure prior to and following dam removal. Here we examine the impacts of the removal of two dams on the Elwha River on the population genetics of O. mykiss. Genetic data were produced from >1200 samples collected prior to dam removal from both life history forms, and post-dam removal from steelhead. We identified three genetic clusters prior to dam removal primarily explained by isolation due to dams and natural barriers. Following dam removal, genetic structure decreased and admixture increased. Despite large O. mykiss population declines after dam construction, we did not detect shifts in population genetic diversity or allele frequencies of loci putatively involved in migratory phenotypic variation. Steelhead descendants from formerly below and above dammed populations recolonized the river rapidly after dam removal, suggesting that dam construction did not significantly reduce genetic diversity underlying O. mykiss life history strategies. These results have significant evolutionary implications for the conservation of migratory adaptive potential in O. mykiss populations above current anthropogenic barriers.

Relationship Timelines, Dyadic Interviews, and Visual Representations: Implementation of an Adapted Visual Qualitative Technique

Increasingly popular in qualitative and mixed-methods research design, visual timelines help organize participants’ life histories with an emphasis on temporality and the context in which important life events and experiences take place. Often, research using timelines focuses on individual participants. Yet, we know that life events, experiences, and decisions that individuals highlight in life history and narrative forms of research are relational in nature. Dyadic interviews allow for participant interaction, exploration of relationality, and the potential for increased breadth and depth in data collection. Recently, LGBTQ+ researchers have begun to evaluate dyadic approaches to timeline research. This paper describes a dyadic approach to timeline development designed to be combined with dyadic narrative interviews. We explain the data elicitation process, utility and value derived from the approach, and detail the development of post hoc linear, graphic timelines. This complementary approach leverages the strengths of dyadic narrative interviews and visual qualitative data synthesis and analysis to explore shared lives in context, highlighting their value as applied in research focused on a sample of sexual minority female couples (a community in which particular types of health disparities have been documented) from across the United States engaged in a series of clinically intensive shared decisions.

A habitat‐based assessment of the role of competition in plant invasions

Abstract Many invasion theories invoke resource competition as the primary mechanism of invader advantage. These include Darwin's naturalization hypothesis (DNH), which treats phylogenetic similarity as a proxy for niche overlap and competitive intensity, and the evolutionary imbalance hypothesis (EIH), which suggests the phylogenetic diversity (PD) of an introduced species’ native range is an indicator of its competitive ability. Few tests of invasion theory, however, consider habitat characteristics associated with the role of competition in community assembly. In particular, plant invasions of habitats characterized by high environmental stress and disturbance levels should rarely be driven by competition. This suggests tests of EIH and DNH are habitat dependent, and their relative importance in invasiveness models should be predictable based on habitat qualities related to competitive intensity. Using a dataset of plant invasions in New Zealand (NZ) natural areas that distinguishes naturalized species according to both habitat type and community impact, we evaluated the predictive ability of factors related to EIH, DNH and covariates including year of introduction, introduction mode and life history attributes, in driving species invasiveness. We hypothesized that EIH and DNH would be more important predictors of invasiveness in forested habitats and decline in importance as communities shifted towards those more dominated by herbaceous species and/or more sparsely vegetated. We found mixed support for the role of competition linked to DNH and EIH as a driver of invasions in relation to habitat type. Native range PD was among the best predictors of invasiveness in forests, and declined in importance in more disturbed habitats, supporting EIH. In contrast, phylogenetic nearest neighbour distance (PNND) of invaders to native communities was more important in disturbed environments, suggesting competition does not drive DNH. Further, for most habitats and across all of NZ, neither PD nor PNND was as important as year of introduction or life history and growth form attributes in predicting invasiveness. Synthesis. Although both native range PD and PNND predict the invasiveness of naturalized plants in NZ, the results of our habitat‐specific models indicate that only PD is consistent with an invasion mechanism based on competitive ability. Effects of PNND were greatest in grasslands that have been extensively modified by fire and grazing, suggesting they are more likely driven by invader pre‐adaptation to modified habitat conditions. Due to the importance of matching species' traits to environmental context, invasiveness risk assessments perform better when applied to invaders of particular habitats.

Kokanee–sockeye salmon hybridization leads to intermediate morphology and resident life history: implications for fisheries management

Stocking programs designed to return extirpated species to their historical range have become increasingly prevalent, punctuating the need to better understand the risks posed to recipient ecosystems. Here, we investigated the genetic and biological consequences of an anadromous sockeye salmon (Oncorhynchus nerka) stocking program in Skaha Lake, British Columbia, where substantial levels of hybridization and introgression with the native freshwater resident ecotype (kokanee) have been detected. We genetically assigned 543 individuals (adult spawners, age-0 juveniles) to estimate stock proportions (pure-stock sockeye, pure-stock kokanee, or hybrid) between 2010 and 2017, with a subset undergoing otolith microchemistry analysis to determine migratory life history and maternal ancestry. The proportion of hybrid spawners varied from 5% to 20% across sampling years, while that of hybrid age-0 juveniles remained relatively constant (∼11%). Hybrid spawners exhibited intermediate size relative to pure stocks, with the vast majority being nonanadromous (92%) and of resident maternal ancestry (76%). Our results provide empirical support for previously hypothesized mechanisms of hybridization between O. nerka life-history forms and underscore the importance of continued monitoring of stocking programs to quantify long-term fitness impacts of introgression and refine management strategies.

Evaluating the potential for prezygotic isolation and hybridization between landlocked and anadromous alewife (Alosa pseudoharengus) following secondary contact.

The recent increase in river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of prezygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith‐derived age estimates. In addition, we analyzed long‐term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3%–13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The degree of spawning time overlap was primarily driven by annual and population‐level variation in the timing of spawning by landlocked alewife, whereas the timing and duration of spawning for anadromous alewife were found to be relatively invariant among years in our study system. For alewife and many other anadromous fish species, the increase in fish passage river restoration projects in the coming decades will re‐establish habitat connectivity and may bring isolated populations into contact. Hybridization between life history forms may occur when prezygotic isolating mechanisms are minimal, leading to potentially rapid ecological and evolutionary changes in restored habitats.

Dam trout: Genetic variability in Oncorhynchus mykiss above and below barriers in three Columbia River systems prior to restoring migrational access.

Restoration of access to lost habitat for threatened and endangered fishes above currently impassable dams represents a major undertaking. Biological monitoring is critical to understand the dynamics and success of anadromous recolonization as, in the case of Oncorhynchus mykiss, anadromous steelhead populations are reconnected with their conspecific resident rainbow trout counterparts. We evaluate three river systems in the Lower Columbia River basin: the White Salmon, Sandy, and Lewis rivers that are in the process of removing and/or providing passage around existing human-made barriers in O. mykiss riverine habitat. In these instances, now isolated resident rainbow trout populations will be exposed to competition and/or genetic introgression with steelhead and vice versa. Our genetic analyses of 2,158 fish using 13 DNA microsatellite (mSAT) loci indicated that within each basin anadromous O. mykiss were genetically distinct from and significantly more diverse than their resident above-dam trout counterparts. Above long-standing natural impassable barriers, each of these watersheds also harbors unique rainbow trout gene pools with reduced levels of genetic diversity. Despite frequent releases of non-native steelhead and rainbow trout in each river, hatchery releases do not appear to have had a significant genetic effect on the population structure of O. mykiss in any of these watersheds. Simulation results suggest there is a high likelihood of identifying anadromous x resident individuals in the Lewis and White Salmon rivers, and slightly less so in the Sandy River. These genetic data are a prerequisite for informed monitoring, managing, and conserving the different life history forms during upstream recolonization when sympatry of life history forms of O. mykiss is restored.

The Genetic Architecture Underlying the Evolution of a Rare Piscivorous Life History Form in Brown Trout after Secondary Contact and Strong Introgression.

Identifying the genetic basis underlying phenotypic divergence and reproductive isolation is a longstanding problem in evolutionary biology. Genetic signals of adaptation and reproductive isolation are often confounded by a wide range of factors, such as variation in demographic history or genomic features. Brown trout (Salmo trutta) in the Loch Maree catchment, Scotland, exhibit reproductively isolated divergent life history morphs, including a rare piscivorous (ferox) life history form displaying larger body size, greater longevity and delayed maturation compared to sympatric benthivorous brown trout. Using a dataset of 16,066 SNPs, we analyzed the evolutionary history and genetic architecture underlying this divergence. We found that ferox trout and benthivorous brown trout most likely evolved after recent secondary contact of two distinct glacial lineages, and identified 33 genomic outlier windows across the genome, of which several have most likely formed through selection. We further identified twelve candidate genes and biological pathways related to growth, development and immune response potentially underpinning the observed phenotypic differences. The identification of clear genomic signals divergent between life history phenotypes and potentially linked to reproductive isolation, through size assortative mating, as well as the identification of the underlying demographic history, highlights the power of genomic studies of young species pairs for understanding the factors shaping genetic differentiation.

Rodent herbivory differentially affects mortality rates of 14 native plant species with contrasting life history and growth form traits.

Ecosystems are transformed by changes in disturbance regimes including wildfire and herbivory. Rodent consumers can have strong top-down effects on plant community assembly through seed predation, but their impacts on post-germination seedling establishment via seedling herbivory need better characterization, particularly in deserts. To test the legacy effects of fire history, and native rodent consumers on seedling establishment, we evaluated factorial combinations of experimental exclusion of rodents and fire history (burned vs. unburned) on seedling survival of 14 native plant species that vary in their life history strategies and growth form in the Mojave Desert. Seedlings were placed into the experimental plots, and seedling survival was monitored daily for 8days. The legacy effects of fire history had minimal effects on seedling survival, but rodent exclusion, year, and their interaction were strongly significant. Seedling survival rates were nearly sixfold greater in rodent exclusion plots compared to control plots in 2012 (53 vs. 9%) and 17-fold greater in 2013 (17 vs. 1%). The dramatic increase in seedling mortality from 2012 to 2013 was likely driven by an increase in rodent abundance and an outbreak of grasshoppers that appears to have intensified the rodent effect. There was strong variability in plant species survival in response to rodent herbivory with annual plants and forb species showing lower survival than perennial plants and shrub species. These results indicate that rodent consumers can strongly regulate seedling survival of native plant species with potentially strong regulatory effects on plant community development.