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USGS2010

Sandhill crane abundance and nesting ecology at Grays Lake, Idaho

We examined population size and factors influencing nest survival of greater sandhill cranes (Grus canadensis tabida) at Grays Lake National Wildlife Refuge, Idaho, USA, during 1997-2000. Average local population of cranes from late April to early May, 1998-2000, was 735 cranes, 34% higher than that reported for May 1970-1971. We estimated 228 (SE = 30) nests in the basin core (excluding renests), 14% higher than a 1971 estimate. Apparent nest success in our study (x?? = 60%, n = 519 nests) was lower than reported for Grays Lake 30-50 years earlier. Daily survival rates (DSRs) of all nests averaged 0.9707 (41.2%). The best model explaining nest survival included year and water depth and their interaction. Nest survival was highest (DSR = 0.9827) in 1998 compared with other years (0.9698-0.9707). Nest survival changed little relative to water depth in 1998, when flooding was extensive and alternative prey (microtines) irrupted, but declined markedly with lower water levels in 2000, the driest year studied. Hypotheses relating nest survival to vegetation height, land use (idle, summer grazing, fall grazing), and date were not supported. In a before-after-control-impact design using 12 experimental fields, nest survival differed among years but not among management treatments (idle, fall graze, fall burn, and summer-graze-idle rotation), nor was there an interaction between year and treatments. However, DSRs in fall-burn fields declined from 0.9781 in 1997-1998 to 0.9503 in 1999-2000 (posttreatment). Changes in the predator community have likely contributed to declines in nest success since the 1950s and 1970s. Our results did not support earlier concerns about effects of habitat management practices on crane productivity. Nest survival could best be enhanced by managing spring water levels. Managers should continue censuses during late April to evaluate long-term relationships to habitat conditions and management.

Journal of Wildlife Management↗

USGS2005

White-tailed deer ecology and management on Fire Island

Deer populations have grown dramatically on Fire Island National Seashore (FIlS) since 1983. Trend data reveal a dichotomy in deer dynamics. In the eastern half of the island, deer density appears to have stabilized between 25-35 deer/km2. In the western half of the island, deer densities are 3-4 times as high in residential communities. Concomitant with that increase has been a general decline in physical stature of some animals, visible impacts on island vegetation, especially in the Sunken Forest, and a perceived increase in the frequency of human and deer interactions. Intensive research on FIlS has shown that deer occupy relatively predictable home ranges throughout the year, but can and do move up and down the island. Impacts of deer on vegetation are most dramatic in the Sunken Forest. Most obvious are the effects of browsing on the herb layer of the Sunken Forest. The least obvious, but perhaps more significant impact is the stark lack of regeneration of canopy tree species since about 1970, which coincides with the initiation of the deer population irruption. A number of herbs and shrubs have been greatly reduced in the understory, and their propagules from the soil. Deer do not readily transmit the bacterium that causes Lyme disease to other organisms, but deer are important hosts for adult ticks which underscores their importance in the transmission pathway of the disease to humans. Deer on FIlS, while occasionally docile, are still wild animals and should be treated as such. Some animals are relatively unafraid of humans due to the absence of predation and a lack of harassment. This in turn has contributed to a longstanding tradition of feeding deer by many residents and visitors, particularly in western portions of the island. Feeding affects both the behavior and population dynamics of deer inhabiting Fire Island. Recent efforts to reduce deer feeding by visitors and residents have been very effective. Ongoing experiments with Porcine Zona Pellucida immunocontraception demonstrate some promise of this technology as a population management tool.. Success appears to be linked directly to factors affecting access to deer, which vary considerably among treatment locations. Continued high National Park Service visibility among communities in the form of interpretive programs, extension and outreach activities, and continued support of research and monitoring of deer and their effects on island biota are keys to successful resolution of persistent issues.

Technical Report↗

USGS2021

Age-structured Jolly-Seber model expands inference and improves parameter estimation from capture-recapture data

Understanding the influence of individual attributes on demographic processes is a key objective of wildlife population studies. Capture-recapture and age data are commonly collected to investigate hypotheses about survival, reproduction, and viability. We present a novel age-structured Jolly-Seber model that incorporates age and capture-recapture data to provide comprehensive information on population dynamics, including abundance, age-dependent survival, recruitment, age structure, and population growth rates. We applied our model to a multi-year capture-recapture study of polar bears (Ursus maritimus) in western Hudson Bay, Canada (20122018), where management and conservation require a detailed understanding of how polar bears respond to climate change and other factors. In simulation studies, the age-structured Jolly-Seber model improved precision of survival, recruitment, and annual abundance estimates relative to standard Jolly-Seber models that omit age information. Furthermore, incorporating age information improved precision of population growth rates, increased power to detect trends in abundance, and allowed direct estimation of age-dependent survival and changes in annual age structure. Our case study provided detailed evidence for senescence in polar bear survival. Median survival estimates were lower (<0.95) for individuals aged <5 years, remained high (>0.95) for individuals aged 722 years, and subsequently declined to near zero for individuals >30 years. We also detected cascading effects of large recruitment classes on population age structure, which created major shifts in age structure when these classes entered the population and then again when they reached prime breeding ages (1015 years old). Overall, age-structured Jolly-Seber models provide a flexible means to investigate ecological and evolutionary processes that shape populations (e.g., via senescence, life expectancy, and lifetime reproductive success) while improving our ability to investigate population dynamics and forecast population changes from capture-recapture data.

PLoS ONE↗

USGS2011

Seasonal timing of first rain storms affects rare plant population dynamics

A major challenge in forecasting the ecological consequences of climate change is understanding the relative importance of changes to mean conditions vs. changes to discrete climatic events, such as storms, frosts, or droughts. Here we show that the first major storm of the growing season strongly influences the population dynamics of three rare and endangered annual plant species in a coastal California (USA) ecosystem. In a field experiment we used moisture barriers and water addition to manipulate the timing and temperature associated with first major rains of the season. The three focal species showed two- to fivefold variation in per capita population growth rates between the different storm treatments, comparable to variation found in a prior experiment imposing eightfold differences in season-long precipitation. Variation in germination was a major demographic driver of how two of three species responded to the first rains. For one of these species, the timing of the storm was the most critical determinant of its germination, while the other showed enhanced germination with colder storm temperatures. The role of temperature was further supported by laboratory trials showing enhanced germination in cooler treatments. Our work suggests that, because of species-specific cues for demographic transitions such as germination, changes to discrete climate events may be as, if not more, important than changes to season-long variables.

Ecology↗

USGS2021

Informing wetland management with waterfowl movement and sanctuary use responses to human-induced disturbance

Long-term environmental management to prevent waterfowl population declines is informed by ecology, movement behavior and habitat use patterns. Extrinsic factors, such as human-induced disturbance, can cause behavioral changes which may influence movement and resource needs, driving variation that affects management efficacy. To better understand the relationship between human-based disturbance and animal movement and habitat use, and their potential effects on management, we GPS tracked 15 dabbling ducks in California over ~4-weeks before, during and after the start of a recreational hunting season in October/November 2018. We recorded locations at 2-min intervals across three separate 24-h tracking phases: Phase 1) two weeks before the start of the hunting season (control (undisturbed) movement); Phase 2) the hunting season opening weekend; and Phase 3) a hunting weekend two weeks after opening weekend. We used GLMM models to analyze variation in movement and habitat use under hunting pressure compared with ‘normal’ observed patterns prior to commencement of hunting. We also compared responses to differing levels of disturbance related to the time of day (high - shooting/~daytime); moderate - non-lethal (~crepuscular); and low - night). During opening weekend flight (% time and distance) more than doubled during moderate and low disturbance and increased by ~50% during high disturbance compared with the pre-season weekend. Sanctuary use tripled during moderate and low disturbance and increased ~50% during high disturbance. Two weeks later flight decreased in all disturbance levels but was only less than the pre-season levels during high disturbance. In contrast, sanctuary use only decreased at night, although not to pre-season levels, while daytime doubled from ~45% to >80%. Birds adjust rapidly to disturbance and our results have implications for energetics models that estimate population food requirements. Management would benefit from reassessing the juxtaposition of essential sanctuary and feeding habitats to optimize wetland management for waterfowl.

Journal of Environmental Management↗

USGS2008

Thermal and energetic constraints on ectotherm abundance: A global test using lizards

Population densities of birds and mammals have been shown to decrease with body mass at approximately the same rate as metabolic rates increase, indicating that energetic needs constrain endotherm population densities. In ectotherms, the exponential increase of metabolic rate with body temperature suggests that environmental temperature may additionally constrain population densities. Here we test simple bioenergetic models for an ecologically important group of ectothermic vertebrates by examining 483 lizard populations. We find that lizard population densities decrease as a power law of body mass with a slope approximately inverse to the slope of the relationship between metabolic rates and body mass. Energy availability should limit population densities. As predicted, environmental productivity has a positive effect on lizard density, strengthening the relationship between lizard density and body mass. In contrast, the effect of environmental temperature is at most weak due to behavioral thermoregulation, thermal evolution, or the temperature dependence of ectotherm performance. Our results provide initial insights into how energy needs and availability differentially constrain ectotherm and endotherm density across broad spatial scales. ?? 2008 by the Ecological Society of America.

Ecology↗

USGS2023

Effects of sucker gigging on fish populations in Oklahoma scenic rivers

Suckers (Catostomidae) are ecologically important, and some support popular fisheries, despite not being considered ‘sport fish’ in most states. Gigging suckers is a popular and culturally significant pastime in the Ozark Highlands, but little is known about the effect of gigging harvest on population dynamics of suckers. Therefore, research is needed to determine safe levels of sucker harvest that ensure sustainability of sucker gigging and protect overall ecosystem function. The objectives of this study were to: 1) determine the spatial distribution of common sucker species during spawning season (when sucker gigging is most effective), 2) determine the population size, age structure , and total mortality rate for common sucker species, and 3) model the effects of different harvest rates on sucker populations to determine the harvest rate at which growth overfishing and recruitment overfishing begin. Suckers were sampled using electrofishing, modified fyke netting, gillnetting, hoop netting, and seining and marked with passive integrated transponder (PIT) tags to provide information about population size, demographics, and coarse-scale movement patterns. A subset of fish sampled using the above gears and additional fish collected during gigging tournaments in 2017-2019 and 2021-2022 (no tournament was held in 2020) were used for age analyses. Tournament data collected prior to the initiation of this project were obtained from the state agency. Data from gigging tournaments indicated Golden Redhorse Moxostoma erythrurum, Black Redhorse M. duquesnei, White Sucker Catostomus commersonii, and Spotted Sucker Minytrema melanops were vulnerable to gigging harvest. Selection by giggers for larger individuals was apparent for all species except Golden Redhorse in 2019. Spotted Suckers constituted most fish harvested, but the proportion of each species harvested still varied among years. A total of 943 fish were aged from samples obtained from 2017 to 2022 and results from subsequent analyses indicated a high degree of variation in growth rates within and among species. Over 4,700 suckers were tagged with PIT tags and over 400 recaptures of these tagged fish were made since autumn 2018. Preliminary analyses indicate survival was consistent across samples and species, and detection rates varied by sampling event (3-month periods). Our most likely top multistrata model suggested that a large portion of fish within the upper Spavinaw, lower Spavinaw, and reservoir sections remain in these locations year-round (means: 0.46 – 0.67). Despite this, transition probabilities are still high for movement from upper Spavinaw to lower Spavinaw (mean: 0.32) and from lower Spavinaw to upper Spavinaw (mean: 0.38). Likewise, transition probabilities were high for movement from lower Spavinaw to the reservoir (mean: 0.15) and from the reservoir to lower Spavinaw (mean: 0.32). Transition probabilities between upper Spavinaw and the reservoir were low in both directions (means < 0.01). Population sizes, growth trajectories and length-weight relationships varied among species. Preliminary harvest models suggest species-specific regulation may be scientifically appropriate; however, it may be difficult for giggers to identify species while gigging. Based on our model results, there appears to be little risk of recruitment or growth overfishing for any species at current exploitation levels.

Oklahoma↗

USGS2024

Ecology of an insular snake assemblage in coastal Maine

Wildlife populations at the peripheries of their distributions or on isolated islands often display divergent and poorly understood morphological or life-history characteristics compared to core populations. We used a capture–mark–recapture dataset collected over a 19-year period to characterize a northern, insular snake assemblage in coastal Maine. We captured 611 individual snakes of 4 species ( Thamnophis sirtalis [Common Gartersnake; n = 221 individuals], Diadophis punctatus [Ring-necked Snake; n = 258 individuals], Storeria occipitomaculata [Red-bellied Snake; n = 81 individuals], and Opheodrys vernalis [Smooth Greensnake; n = 51 individuals]) and recorded 104 recaptures. We provide some of the first data on growth, reproduction, and movement for these species in northern New England, expanding our understanding of insular and northern snake populations. Specifically, we found that Common Gartersnakes fed primarily on earthworms and amphibians and grew rapidly, in accordance with mainland populations, but exhibited smaller size at maturity and average litter sizes. We captured an unusually large number of Ring-necked Snakes, which are uncommon elsewhere in Maine, and recorded an apparently localized nesting area for this species, as well as relatively long-distance (230–300 m) dispersal away from that location. In our population, female Ring-necked Snakes mature in their third year, and this species exhibits weak sexual size dimorphism (SSD). We found the ecology of Red-bellied Snakes at our study site to be similar to other populations, with individuals feeding on slugs, and females maturing in their second year; however, our population exhibited the strongest pattern of (female-biased) SSD. Smooth Greensnakes were restricted to the most extensive old-field habitat within our study site and fed on a variety of arthropods. We confirmed communal nesting and short incubation period for this species and provide among the first data on growth and longevity (at least 7 years) of this relatively understudied species.

Maine↗

USGS2014

Identifying monitoring gaps for amphibian populations in a North American biodiversity hotspot, the southeastern USA

I review the primary literature to ascertain the status of amphibian monitoring efforts in the southeastern USA, a “hotspot” for biodiversity in North America. This effort revealed taxonomic, geographic and ecological disparities in studies of amphibian populations in this region. Of the species of anurans and caudates known to occur in the Southeast, 73.8 and 33.3 %, respectively, have been monitored continuously for at least 4 years. Anurans are generally shorter-lived than are caudates and, thus, have been studied for the equivalent of at least one population turnover more than have caudates. The percentage of species (of those occurring in a given state) monitored continuously for at least 4 years was lowest for Alabama and Mississippi and highest for Florida for both taxa. The vast majority of studies (69.6 %) were conducted on species that inhabit natural freshwater wetlands, in contrast to other aquatic and terrestrial habitats. Species considered threatened by the International Union for Conservation of Nature comprised only 7.7 % of 65 species that have been studied consistently. The majority of comparative studies of contemporary versus historical occurrences were potentially biased by the use of “presence-only” historical data and resurveys of short duration. Other issues, such as inadequate temporal and spatial scale and neglect of different sources of error, were common. Awareness of these data gaps and sampling and statistical issues may help facilitate informed decisions in setting future monitoring priorities, particularly with respect to species, habitats and locations that have been largely overlooked in past and ongoing studies.

Alabama, Florida, Georgia, Louisiana, Mississippi,↗

USGS2019

Planning for ecological drought: Integrating ecosystem services and vulnerability assessment

As research recognizes the importance of ecological impacts of drought to natural and human communities, drought planning processes need to better incorporate ecological impacts. Drought planning currently recognizes the vulnerability of some ecological impacts from drought (e.g., loss of instream flow affecting fish populations). However, planning often does not identify all the ecological aspects in a landscape that stakeholders value, nor does it examine the extent to which those aspects are vulnerable to drought. One approach for identifying ecological aspects is ecosystem services (ES) -- i.e., the benefits humans receive from nature. To incorporate ecological impacts into drought planning in the Upper Missouri Headwaters region (Montana, USA), we combined ES elicitation using the Common International Classification of Ecosystem Services and a vulnerability assessment using semi-structured interviews. We juxtaposed results from the interviews and the ES elicitation to assess which ES might be vulnerable to drought and which impacts from interviews were associated with losses of ES. While both methods suggested common drought vulnerabilities, each method also suggested drought vulnerabilities not reported using the other method. The ES elicitation produced more detail about services present in the UMH ecosystem today while interviews resulted in more discussion about ecological transformation from future droughts. Results suggest that some combination of open-ended vulnerability assessment methods and ES elicitation using a structured framework can result in greater understanding of ecological drought vulnerability in a given region.

Montana↗

USGS2011

Millennial precipitation reconstruction for the Jemez Mountains, New Mexico, reveals changing drought signal

Drought is a recurring phenomenon in the American Southwest. Since the frequency and severity of hydrologic droughts and other hydroclimatic events are of critical importance to the ecology and rapidly growing human population of this region, knowledge of long-term natural hydroclimatic variability is valuable for resource managers and policy-makers. An October–June precipitation reconstruction for the period AD 824–2007 was developed from multi-century tree-ring records of Pseudotsuga menziesii (Douglas-fir), Pinus strobiformis (Southwestern white pine) and Pinus ponderosa (Ponderosa pine) for the Jemez Mountains in Northern New Mexico. Calibration and verification statistics for the period 1896–2007 show a high level of skill, and account for a significant portion of the observed variance (>50%) irrespective of which period is used to develop or verify the regression model. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1896–2007). A recent segment of the reconstruction (2000–2006) emerges as the driest 7-year period sensed by the trees in the entire record. That this period was only moderately dry in precipitation anomaly likely indicates accentuated stress from other factors, such as warmer temperatures. Correlation field maps of actual and reconstructed October–June total precipitation, sea surface temperatures and 500-mb geopotential heights show characteristics that are similar to those indicative of El Niño–Southern Oscillation patterns, particularly with regard to ocean and atmospheric conditions in the equatorial and north Pacific. Our 1184-year reconstruction of hydroclimatic variability provides long-term perspective on current and 20th century wet and dry events in Northern New Mexico, is useful to guide expectations of future variability, aids sustainable water management, provides scenarios for drought planning and as inputs for hydrologic models under a broader range of conditions than those provided by historical climate records.

New Mexico↗

USGS2005

Relation of desert pupfish abundance to selected environmental variables in natural and manmade habitats in the Salton Sea basin

We assessed the relation between abundance of desert pupfish, Cyprinodon macularius, and selected biological and physicochemical variables in natural and manmade habitats within the Salton Sea Basin. Field sampling in a natural tributary, Salt Creek, and three agricultural drains captured eight species including pupfish (1.1% of the total catch), the only native species encountered. According to Bray-Curtis resemblance functions, fish species assemblages differed mostly between Salt Creek and the drains (i.e., the three drains had relatively similar species assemblages). Pupfish numbers and environmental variables varied among sites and sample periods. Canonical correlation showed that pupfish abundance was positively correlated with abundance of western mosquitofish, Gambusia affinis, and negatively correlated with abundance of porthole livebearers, Poeciliopsis gracilis, tilapias (Sarotherodon mossambica and Tilapia zillii), longjaw mudsuckers, Gillichthys mirabilis, and mollies (Poecilia latipinnaandPoecilia mexicana). In addition, pupfish abundance was positively correlated with cover, pH, and salinity, and negatively correlated with sediment factor (a measure of sediment grain size) and dissolved oxygen. Pupfish abundance was generally highest in habitats where water quality extremes (especially high pH and salinity, and low dissolved oxygen) seemingly limited the occurrence of nonnative fishes. This study also documented evidence of predation by mudsuckers on pupfish. These findings support the contention of many resource managers that pupfish populations are adversely influenced by ecological interactions with nonnative fishes. ?? Springer 2005.

California↗

USGS2025

Electric field-induced detachment and vibration analysis for Sea Lamprey

Objective: Sea lamprey Petromyzon marinus , a known ecological threat to native fish populations in the Great Lakes, use their oral suction disc to navigate challenging environments when moving upstream to spawn. This study investigated the physiological response of adult sea lamprey to detach under pulsed direct current electric fields. Methods: Adult sea lampreys in an attaching position were exposed to pulsed direct current electric fields at four different field strengths (0.7, 1.1, 1.3, and 1.9 V/cm). Behavioral responses, including detachment and vibration, were observed and analyzed. Fast Fourier Transform analysis was applied to vibration data to quantify the frequency of vibration exhibited by non-detached sea lamprey. Statistical correlations between detachment rates and vibration responses to sea lamprey sex, weight, and length were evaluated to determine influencing factors. Results: The highest detachment rate (91%) was observed at 1.1 V/cm, with the detachment rate above 70% for other field strengths. Fast Fourier Transform analysis revealed that the vibration frequencies closely matched the signal while stronger fields elicited a more pronounced vibration amplitude without significantly increasing detachment. Non-detached sea lampreys exhibited “twitching” behavior synchronized with the electric field frequency. Sex, weight, and length had minimal influence on detachment rates and vibration responses. Conclusion: This study provided insights into the behavioral responses of sea lamprey under electric fields, highlighting the potential for optimizing electric deterrents for selective control. While not all sea lampreys detach during electroshocking, understanding their behavior can be crucial in maximizing detachment rates and contributing to improved management strategies for this invasive species.

Transactions of the American Fisheries Society↗

USGS2008

Evolutionary divergence of giant tortoises in Galapagos

The giant tortoises in the Galapagos Archipelago diverge considerably in size, and in shape and other carapace characteristics. The saddleback morphotype is known only from insular faunas lacking large terrestrial predators (i.e. Galapagos and Mauritius) and in Galapagos is associated with xeric habitats where vertical feeding range and vertical reach in agonistic encounters are adaptive. The large domed morphotype is associated with relatively cool, mesic habitats where intraspecific competition for food and other resources may be less intense than in xeric habitats. Other external characteristics that differ between tortoise populations are also correlated with ecological variation. Tortoises have radiated into a mosaic of ecological conditions in the Galapagos but critical data are lacking on the role of genetic and environmental controls on phenotypic variation. Morphological divergence in tortoises is potentially a better indicator of present ecological conditions than of evolutionary relationships.

Galapagos Islands↗

USGS2024

Factors influencing the prevalence of hyperpigmented melanistic lesions in smallmouth bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania

Hyperpigmented melanistic lesions (HPMLs) are a visual anomaly documented on the skin of smallmouth bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania and in numerous other geographical locations. Currently, there is a lack of information on environmental and fish characteristics that may influence the prevalence of HPMLs associated with a recently described Adomavirus . The goal of this study was to understand potential drivers associated with HPMLs in socioeconomically and ecologically important riverine smallmouth bass populations. A total of 16,220 smallmouth bass were collected and examined for HPMLs between 2012 and 2022 in the Susquehanna River Basin. Overall, HPMLs were documented on 2.9% of fish collected. The interaction between temperature and fish size suggested differing relationships between shorter and longer fish with respect to temperature. Predicted probability of HPML prevalence ranged from 1.1% (95% CI = 0.3, 3.2) at 4°C to 0.01% (CI = 0.00, 0.04) at 26°C for an age-0 (125 mm) fish. In contrast, predicted probability of HPML prevalence ranged from 10.5% (95% CI = 5.8, 18.9) at 4°C to 0.8% (CI = 0.4, 1.5) at 26°C for an adult (322 mm) fish. Overall, HPMLs were more common in longer fish during cooler temperature periods which also corresponds to key life history periods for smallmouth bass (e.g., pre-spawn and overwintering) and could represent different exposure histories for juvenile and adult fish.

Pennsylvania↗

USGS2026

Assessment of Chinook Salmon smolt survival at offsite release locations in the Sacramento River across wet and dry years

We used acoustic telemetry to estimate survival of tagged release groups, and quantify differences between alternative hatchery release strategies. To assess whether offsite release could increase survival of hatchery fish relative to those released at the hatchery, we compare survival during emigration of hatchery fall Chinook Salmon (FCS, Oncorhynchus tshawytscha ) smolts released onsite, at Coleman National Fish Hatchery (NFH), to those released at alternative offsite locations downstream in the upper Sacramento River, California. Approximately 300 fish in each release group were implanted with acoustic tags in the 3-year study during 2019, 2021, and 2022. Environmental conditions in the emigration corridor varied between study years, with extended high flows in 2019, whereas drought conditions and a flat hydrograph occurred in 2021 and 2022. Survival across years appeared to reflect environmental conditions, with higher overall survival seen in 2019. Survival differences between release sites generally showed higher cumulative survival to Knights Landing or Chipps Island for the downstream release groups, compared to the onsite releases during 2021 and 2022. This information suggests hatchery releases of FCS from Coleman NFH at downstream release sites may benefit emigration survival during years of drought and sub-optimal in-river conditions, compared to standard onsite releases. Hatchery managers can use information from this study to diversify the portfolio of release strategies, which may be useful to buffer against extreme variations of adult abundance by spreading risks across space and time. Ultimately, offsite releases may be a useful tool for adaptive management of these culturally, ecologically, and economically important salmon populations.

California↗

USGS2008

Length variation in age-0 westslope cutthroat trout at multiple spatial scales

Phenotypic diversity provides ecological and evolutionary functions, stabilizing populations in variable environments. Although benefits of larger body size in juvenile fishes are well documented, size variation may have value as well. We explored the distribution of length and length variation in age-0 westslope cutthroat trout Oncorhynchus clarkii lewisi at three spatial scales: area (102 km2), stream (101 km2), and site (100 km2). In addition, we examined relationships between length variables (mean length and interquartile range of length) and instream (temperature and conductivity) and landscape (aspect, elevation, headwater distance, and valley width) variables that were expected to be associated with fish size. Conductivity was included as a surrogate for productivity. Most variation in mean length and interquartile range of fish length was found among areas (62.2% and 62.6%, respectively). Mean length also varied among streams and sites (21.9% and 15.8%, respectively). Similarly, interquartile range of fish length varied among streams and sites (19.1% and 18.3%, respectively). Both length variables were associated with temperature and elevation. Mean fish length was also associated with conductivity, but the association between interquartile length range and conductivity was weak. We conclude that the conservation of variation in phenotypic attributes, such as length, in westslope cutthroat trout may require conservation of viable populations across broad areas and across environmental gradients that are associated with growth. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗

USGS2007

Population inertia and its sensitivity to changes in vital rates and population structure

Because the (st)age structure of a population may rarely be stable, studies of transient population dynamics and population momentum are becoming ever more popular. Yet, studies of "population momentum" are restricted in the sense that they describe the inertia of population size resulting from a demographic transition to the stationary population growth rate. Although rarely mentioned, inertia in population size is a general phenomenon and can be produced by any demographic transition or perturbation. Because population size is of central importance in demography, conservation, and management, formulas relating the sensitivity of population inertia to changes in underlying vital rates and population structure could provide much-needed insight into the dynamics of populations with unstable (st)age structure. Here, we derive such formulas, which are readily computable, and provide examples of their potential use in studies of life history and applied arenas of population study. ?? 2007 by the Ecological Society of America.

Ecology↗