Biology subjects

Walter, J. A.

Publications and source records attributed to Walter, J. A..

5 recordsLinked to original sources

bioRxiv2023

How environmental drivers of spatial synchrony interact

Spatial synchrony, the tendency for populations across space to show correlated fluctuations, is a fundamental feature of population dynamics, linked to central topics of ecology such as population cycling, extinction risk, and ecosystem stability. A common mechanism of spatial synchrony is the Moran effect, whereby spatially synchronized environmental signals drive population dynamics and hence induce population synchrony. After reviewing recent progress in understanding Moran effects, we here elaborate a general theory of how Moran effects of different environmental drivers acting on the same populations can interact, either synergistically or destructively, to produce either substantially more or markedly less population synchrony than would otherwise occur. We provide intuition for how this newly recognized mechanism works through theoretical case studies and application of our theory to California populations of giant kelp. We argue that Moran interactions should be common. Our theory and analysis explain an important new aspect of a fundamental feature of spatiotemporal population dynamics.

ecology↗

bioRxiv2022

Habitat use differences mediate anthropogenic threat exposure in white sturgeon

Understanding intraspecific variation in habitat use, particularly of long-lived fishes across multiple life history stages, is core to improved conservation management. Here, we present results from a synthesis of acoustic telemetry data for large juvenile and adult white sturgeon (Acipenser transmontanus) from 2010 to 2017 in the San Francisco Estuary and Sacramento River ecosystems. We focused primarily on uncovering spatial patterns of inferred habitat occupancy across life stages, and on linking habitat use to population threats. We found substantial differences in habitat use across individuals and over time that was related to fish age class. However, differences in habitat use were not explained by fish sex or water year flow conditions. We estimated an index of angling exposure, which showed that fish entering reproductive maturity, which historically were of harvestable size, were detected less often than other sizes in areas with high angler pressure, suggesting possible behavioral avoidance of areas of high angler pressure. Additionally, we used historical data to evaluate potential exposure of white sturgeon to a severe red tide event in late summer 2022. We found that >50% of reproductive-age fish may have been residing in areas affected by the red tide. Future monitoring and management of white sturgeon might benefit from examining multiple phases of white sturgeon life history. For example, additional tracking studies could improve understanding of juvenile habitat use, adult survival rates, patterns of anadromy, and cross-basin habitat utilization.

ecology↗

bioRxiv2021

Geographic variation in larval cold tolerance and exposure across the invasion front of a widely established forest insect

As the global climate changes, high and low temperature extremes can drive changes in species distributions. Across the range of a species, thermal tolerance can experience plasticity and may undergo selection, shaping resilience to temperature stress. In this study, we measured variation in the lower thermal tolerance of early instar larvae of an invasive forest insect, Lymantria dispar dispar L. (Lepidoptera: Erebidae), using populations sourced from the climatically diverse invasion of the Eastern United States. In two chill coma recovery experiments, we recorded recovery time following a period of exposure to a non-lethal cold temperature. A third experiment quantified growth responses after chill coma recovery to evaluate sublethal effects. Our results indicate that cold tolerance is linked to regional climate, with individuals from cold climate populations recovering faster from chill coma. While this geographic gradient is seen in many species, detecting this pattern is notable for an introduced species founded from a single point-source introduction. We demonstrate that the cold temperatures used in our experiments occur in nature from cold snaps after spring hatching, but negative impacts to growth and survival appear low. We expect that population differences in cold temperature performance manifest more from differences in temperature-dependent growth than acute exposure. Evaluating intraspecific variation in cold tolerance increases our understanding of the role of climatic gradients on the physiology of an invasive species, and contributes to tools for predicting further expansion. Summary StatementChill coma recovery experiments demonstrate geographic variation in cold temperature tolerance for a widespread invasive species, and the risk of early season exposure differs across the invasion front.

physiology↗

bioRxiv2021

Using simulated temperature regimes to test growth and development of an invasive forest insect under climate change

Temperature and its impact on fitness are fundamental for understanding range shifts and population dynamics under climate change. Geographic climate heterogeneity, behavioural and physiological plasticity, and thermal adaptation to local climates makes predicting the responses of species to climate change complex. Using larvae from seven geographically distinct wild populations in the eastern United States of the non-native forest pest Lymantria dispar dispar (L.), we conducted a simulated reciprocal transplant experiment in environmental chambers using six custom temperature regimes representing contemporary conditions near the southern and northern extremes of the US invasion front and projections under two climate change scenarios for the year 2050. Larval growth rates increased with climate warming compared to current thermal regimes and responses differed by population. A significant population-by-treatment interaction indicated that growth rates increased more when a source population experienced the warming scenarios for their region, especially for southern populations. Our study demonstrates the utility of simulating thermal regimes under climate change in environmental chambers and emphasizes how the impacts from future increases in temperature can be heterogeneous due to geographic differences in climate-related performance among populations.

ecology↗

bioRxiv2021

Intraspecific variation in migration timing of green sturgeon in the Sacramento River system

BackgroundUnderstanding movement patterns of anadromous fishes is critical to conservation management of declining wild populations and preservation of habitats. Yet, infrequent observations of individual animals fundamentally constrain accurate descriptions of movement dynamics. MethodsIn this study, we synthesized over a decade (2006-2018) of acoustic telemetry tracking observations of green sturgeon (Acipenser medirostris) in the Sacramento River system to describe major anadromous movement patterns. ResultsWe observed that green sturgeon exhibited a unimodal in-migration during the spring months but had a bimodal distribution of out-migration timing, split between an early out-migration (32%) group during May - June, or alternatively, holding in the river until a late out-migration (68%), November - January. Focusing on these out-migration groups, we found that river discharge, but not water temperature, may cue the timing of migration, and that fish showed a tendency to maintain out-migration timing between subsequent spawning migration events. ConclusionsWe recommend that life history descriptions of green sturgeon in this region reflect the distinct out-migration periods described here. Furthermore, we encourage the continued use of biotelemetry to describe migration timing and life history variation, not only this population but other green sturgeon populations and other species.

ecology↗