Biology subjects

Ohlberger, J.

Publications and source records attributed to Ohlberger, J..

4 recordsLinked to original sources

bioRxiv2024

Accounting for salmon body size declines in fishery management can reduce conservation risks

Changes in population demographic structure can have tangible but unknown effects on management effectiveness. Fishery management of Pacific salmon is often informed by estimates of the number of spawners expected to produce maximum sustainable yield (SMSY), which implicitly assumes that reproductive output per spawner does not change over time. However, many salmon populations have experienced long-term trends in age, sex, and length-at-age compositions that have resulted in smaller body sizes of mature fish. We present an empirically-based simulation approach for evaluating management implications of declining reproductive output that results from shifting demographics. We simulated populations with or without demographic trends, selective or unselective harvests, and harvest policies based on assessment methods that did or did not account for demographic trends when estimating SMSY. A management strategy evaluation showed that expected mean harvests and run sizes were reduced when populations exhibited negative demographic trends. Reduced abundances and increased conservation risks could be partially mitigated by using a stock-recruit analysis based on egg mass instead of spawner abundance, or by using a precautionary management strategy where target escapements were higher than the estimated SMSY, especially in fisheries that selectively removed large fish. Accounting for demographic trends in stock-recruit analyses resulted in up to 25% higher run sizes and up to 20% lower conservation risks compared to traditional methods when trends toward smaller, younger, and male-biased runs were present in the population. Conservation of population demographic structure may be critical for sustaining productive fish populations and their benefits to ecosystems and people.

ecology↗

bioRxiv2024

Non-linear growth-temperature relationship leads toopposite responses to warming in cold versus warmpopulations

Body size is a key functional trait that has declined in many biological communities, partly due to changes in individual growth rates in response to climate warming. However, our understanding of growth responses in natural ecosystems is limited by relatively short time series without large temperature contrasts and unknown levels of adaptation to local temperatures across populations. In this study, we collated back-calculated length-at-age data for the fish Eurasian perch (Perca fluviatilis) from 10 populations along the Baltic Sea coast between 1953-2015 (142023 length-at-age measurements). We fitted individual-level growth trajectories using the von Bertalanffy growth equation, and reconstructed local temperature time series using generalized additive models fitted to three data sources. Leveraging a uniquely large temperature contrast due to climate change and artificial heating, we then estimated population-specific and global growth-temperature relationships using Bayesian mixed models, and evaluated if they conformed to local adaption or not. We found little evidence for local adaptation in the temperature-dependence of individual growth curves. Instead, population-specific curves mapped onto a global curve, resulting in body growth increasing with warming in cold populations but decreasing in warm populations. Understanding to which degree the effects of warming on growth and size are population-specific is critical for generalizing predictions of climate impacts on growth, which is a key biological trait affecting multiple levels of biological organisation from individuals to ecosystem functioning.

ecology↗

bioRxiv2021

Optimum growth temperature declines with body size within fish species

According to the temperature-size rule, warming of aquatic ecosystems is generally predicted to increase individual growth rates but reduce asymptotic body sizes of ectotherms. However, we lack a comprehensive understanding of how growth and key processes affecting it, such as consumption and metabolism, depend on both temperature and body mass within species. This limits our ability to inform growth models, link experimental data to observed growth patterns, and advance mechanistic food web models. To examine the combined effects of body size and temperature on individual growth, as well as the link between maximum consumption, metabolism and body growth, we conducted a systematic review and compiled experimental data on fishes from 52 studies that combined body mass and temperature treatments. By fitting hierarchical models accounting for variation between species, we estimated how maximum consumption and metabolic rate scale jointly with temperature and body mass within species. We found that whole-organism maximum consumption increases more slowly with body mass than metabolism, and is unimodal over the full temperature range, which leads to the prediction that optimum growth temperatures decline with body size. Using an independent dataset, we confirmed this negative relationship between optimum growth temperature and body size. Small individuals of a given population may therefore exhibit increased growth with initial warming, whereas larger conspecifics could be the first to experience negative impacts of warming on growth. These findings help advance mechanistic models of individual growth and food web dynamics and improve our understanding of how climate warming affects the growth and size structure of aquatic ectotherms.

ecology↗

bioRxiv2018

Size-based ecological interactions drive food web responses to climate warming

Predicting the impacts of climate change on animal populations and communities requires understanding of feedbacks between direct physiological responses and indirect effects via ecological interactions. Food-dependent body growth and within-species size variation have major effects on dynamics of populations and communities through feedbacks between individual performance and population size structure. Moreover, evidence suggests a link between temperature and population size structure, but we lack an understanding of how this is mediated by species interactions when life history processes are food-dependent. Here, we use a dynamic stage-structured biomass model with food-, size- and temperature-dependent life history processes to assess how temperature affects coexistence, stability and size structure in a tri-trophic food chain. We show that predator biomass densities decline with warming either gradually or in the form of collapses, depending on which consumer life stage they predominantly feed on. Collapses occur when warming destabilizes the community and induces alternative stable states via Allee effects, which emerge when predators promote their own food source through predation. By contrast, warming at low temperatures stabilizes the community as limit cycles turn to fixed point dynamics, unless predators feed only on juveniles. Elevated costs of being large in warmer environments accelerate the decline in predator persistence and mean body size of the community. These results suggest that predator persistence in warmer climates may be lower than previously acknowledged when accounting for size- and food-dependence of life history processes, and that interactions within and between species can mediate the effects of warming on food web stability.\n\nSignificanceClimate warming is altering the dynamics and structure of aquatic ecosystems worldwide. Predicting food web reorganization under rising temperatures requires an understanding of physiological responses and ecological interactions of organisms, both of which depend on body size. We show that size variation within species, food-dependent growth and ecological interactions critically affect how food chains respond to warming. Specifically, warming can stabilize or destabilize food chains and expose predators to increased risk of sudden collapses, resulting in alternative stable food web states. Increasing temperatures can cause abrupt reductions in mean community body size, primarily due to loss of top predators. The potential loss of biodiversity and shifts in ecosystem stability are among the major challenges caused by a warming climate.

ecology↗