Oecologia最新文献

Due to ongoing climate change, extreme climatic events are expected to increase in magnitude and frequency. While individual species' responses to thermal extremes are widely studied, the impact of extreme heat events on species interactions and the key functions they provide in communities is understudied. As outcomes of species interactions depend on coordinated physiology and development, the consequences of heat exposure are likely impacted by its timing relative to the organisms' life history traits, but to what extent is unclear. In this study, we evaluate how the timing of heat exposure affects interactions among nine tropical Drosophila-parasitoid species combinations using laboratory microcosm experiments. Interactions were most affected when heat exposure coincided with parasitism, leading to decreased parasitism rates. Parasitism rates also dropped when extreme heat occurred after parasitism in one instance. Experiencing heat exposure before parasitism had little effect. Using a simulation model, we determined that the combined effects of parasitism and heat exposure are generally additive, with no evidence of delayed consequences of heat exposure early in development on parasitism outcomes. Furthermore, we found adult host flies and parasitoids more resistant to heat exposure than their larval stages. Thus, whether more frequent extreme heat events disrupt species interactions globally will depend on their exact timing relative to ontogenetic stages and interactions. Heat exposure impacts the two trophic levels differently. Thus, when heat exposure coincides with parasitism, it may diminish the ability of parasitoids to control their hosts, affecting both natural ecosystems and agricultural environments.

Disturbance and dispersal processes jointly shape assemblage structures across multiple spatial scales. The flood pulse in Amazon rivers is a large-scale natural and seasonal disturbance that affects floodplain forests and fluvial islands. We evaluated how flooding and isolation of fluvial islands act as environmental filters, structuring taxonomic and functional ant assemblages in the Amazon. During the dry season, we collected ground-dwelling and arboreal ants in 12 transects in terra-firme (non-flooded forest), 12 in igapó (flooded forest connected with terra-firme), and 11 in fluvial islands (flooded forest isolated from terra-firme and igapó) in Anavilhanas National Park, Amazonas, Brazil. We recorded 205 ant species and morphospecies. The arboreal ant richness was similar between the environments, but terra-firme forest harbored higher richness in the ground stratum. Ant composition strongly differed between the environments, and the turnover dominates the beta diversity patterns in both the ground and arboreal strata. Cryptobiotic attines, ground-dwelling specialist predators, and raid-hunting predators were extremely rare or absent, while arboreal predators and generalist omnivores were relatively more abundant in fluvial islands. Flooding and spatial isolation were related to ant assemblage structure promoting strong species turnover in fluvial islands. Ant species that exclusively live on the ground can only survive where the influence of floods is minimal because it reduces nesting sites and availability of food resources. Since ant composition is markedly different between environments, fluvial islands contributed to regional turnover in ant species diversity, increasing the conservation value of this habitat at larger scales.

Low concentrations of calcium have been found to slow growth and reproduction of the freshwater zooplankton, Daphnia. Despite experimental evidence linking poor animal performance and low calcium concentrations, there are no theoretical models that link calcium uptake dynamics to Daphnia growth. Here I created a multi-element (carbon (C), phosphorus (P), and calcium (Ca)) model of Daphnia growth that incorporates information on animal Ca uptake and loss, feeding rates, C and P absorption efficiencies, and body nutrient content. This model examines how the relative supplies of Ca, C, and P in food and water affect Daphnia's acquisition of these elements and subsequently, their growth rates. The model demonstrates that animal limitation by Ca switches to C or P with changes in food abundance and C:P ratios above a threshold Ca concentration. While modelled threshold Ca concentrations were remarkably similar to previous empirical estimates, Daphnia growth rates predicted by the model were generally much lower than those previously reported for animals experimentally raised under low Ca concentrations. Further, the model predicts Daphnia to be primarily food quantity or P-limited in lakes of south-central Ontario due to relatively low supply of food C and/or P compared to Ca. While this model would benefit from additional data on Ca uptake parameters, it nonetheless shows the utility of multi-element mass-balance modeling and provides an approach to determine the frequency and strength of Ca-limitation in zooplankton populations in lake ecosystems.

Under predation risk, prey face tradeoffs between foraging, reproduction, and predator avoidance. These tradeoffs can affect life history traits, such as growth, reproduction, and lifespan. By increasing the risk of death, predators can cause prey to prioritize current reproduction at the expense of future reproduction, resulting in earlier reproduction, less growth, and reduced lifespan. Alternatively, predators can cause prey to invest energy in defensive morphology or growth at the expense of reproduction, resulting in reduced or delayed reproduction, larger size, and longer lifespan. Finally, responding to predators can be costly to prey. For example, the energetic cost from reduced foraging can potentially reduce growth, reproduction, and lifespan. Exposing prey to predation risk at different parts of the lifespan can disentangle these potential mechanisms. In this experiment, we tested how the timing of predation cues affects the life history of a freshwater snail pond snail (Physa acuta). We exposed the snails to predation cues in early life (post-hatching to 39 days old), late life (39 to 78 days old), or both and measured how predation exposure early and late in life affected growth, age at first reproduction, total reproduction, and life expectancy. We found that exposure to predation during early life led to a delay in first reproduction, lower life expectancy, and lower fecundity, regardless of cue removal later in life. Exposure to predation cues in late life had no effect on growth, life expectancy, or reproduction. These results suggest a developmental window in which predation risk affects life history traits and suggest a potential cost to prey responding to predators early in life.

Both theory and observations suggest that tree intrinsic water use efficiency (iWUE)-the ratio of photosynthetic carbon assimilation to stomatal conductance to water-increases with atmospheric CO₂. However, the strength of this relationship varies across sites and species, prompting questions about additional physiological constraints and environmental controls on iWUE. In this study, we analyzed tree core carbon isotope ratios to examine trends in, and drivers of, iWUE in 12 tree species common to the temperate forests of eastern North America, where forests have experienced changes in CO₂, climate, and atmospheric pollution in recent decades. Across all site-species combinations, we found that tree iWUE increased 22.3% between 1950 and 2011, coinciding with a 25.2% increase in atmospheric CO₂. iWUE trajectories varied markedly among tree functional groups and within species across sites. Needleleaf evergreen iWUE increased until circa 2002 before declining in recent years, while iWUE of broadleaf deciduous species continued to increase. The analysis of environmental controls on iWUE trends revealed smaller increases in iWUE in trees subjected to higher atmospheric pollution loads. Our results suggest that tree functional characteristics and atmospheric pollution history influence tree response to atmospheric CO₂, with implications for forest carbon and water balance in temperate regions.

Global climate change exposes small endotherms to high ambient temperatures (T_a), increasing the risk of dehydration and hyperthermia. These threats are disproportionately severe on cold adapted small endotherms with limited heat tolerance. Using temperature telemetry and flow through respirometry, we investigated the thermoregulatory strategies of lesser long-eared bats (Nyctophilus geoffroyi) inhabiting a temperate ecosystem. We predicted this population would have low heat tolerance limits and would initiate active thermoregulation at low T_as. We also predicted that, similar to other populations, females would have higher heat tolerance limits and a more conservative water economy than males given their reproductive ecology places a high demand on water reserves. In line with our predictions, the subcutaneous temperature (T_sub), whole animal resting metabolic rate (waRMR) and whole animal evaporative water loss (waEWL) data suggest that they experience heat stress at low T_as. Females could tolerate higher experimental T_as (females = 44 ℃, males = 42 ℃) and initiated evaporative cooling at a significantly higher T_a (37.7 ℃) than males (33.1 ℃), which is considerably lower than other populations of the same species adapted to arid environments. Our results highlight how different environment conditions and contrasting reproductive ecologies between sexes influence the thermoregulatory capacities and strategies of small endotherms. Although this population does not currently face consistent threats from lethal hyperthermia or dehydration, increasing T_as could expose them to sub-lethal fitness costs such as progressive mass loss due to higher energy expenditure for thermoregulation.

This study examines the effects of three light regimes-1) photosynthetic light (PAR) only, 2) PAR + UV-A, and 3) PAR + UV-A + UV-B radiation-on area and biomass growth in two old forest lichens: the widely distributed Lobaria pulmonaria, noted for rapid growth, and the rarer L. virens, with previously undocumented growth rates but known susceptibility to high light. To overcome the constraints of artificial light sources, we utilized solar filters in sun-exposed field conditions to assess how UV impacts growth and influences mycobiont traits (melanic pigmentation, thallus thickness) and photobiont responses (Chl content, Chl fluorescence, CO₂ uptake). While UV exposure significantly reduced growth rates, it did not impact photobiont processes. Lobaria pulmonaria demonstrated robust melanin synthesis under UV-B, preventing photoinhibition and safeguarding chlorophylls, whereas L. virens, with lower melanin production, showed reduced Chl content and increased vulnerability to solar radiation. Enhanced specific thallus mass, a proxy of water holding capacity, correlated with increased melanic pigmentation, suggesting that UV-B also aids in acclimation of drought tolerance. Despite reduced growth, UV exposure promotes acclimation to environmental stressors, revealing a trade-off between growth and acclimation. These findings challenge previous assumptions regarding UV-B susceptibility in shade-adapted old forest lichens and underscore the intricate interplay between lichen growth and acclimation.

Plants have to allocate resources into their growth and reproduction but also in phytochemicals used in interactions with their environment. Some species display an extraordinarily high diversity of such phytochemicals, called chemodiversity. In stands with different neighbors, plot chemodiversity may be even higher and provide associational resistance. Little is known about trade-offs in investment into growth and reproduction versus chemodiversity in plant individuals growing in chemically different neighborhoods.We investigated such trade-offs using the perennial Tanacetum vulgare, which shows differences in leaf terpenoid composition, forming distinct chemotypes. We planted plots consisting of five plants of one of five chemotypes (homogenous neighborhoods) and plots consisting of five different chemotypes (heterogenous) in a field. Plants within each block were offspring from different mother plants (here called maternal genotypes). Over 2 years, plant performance traits related to growth and reproduction were recorded and the leaf terpenoid profiles were measured once. Depending on the chemotype, plants had significantly different chances of flowering. Plants in heterogenous plots produced a higher maximum number of flower heads than those in homogenous plots. The maternal genotype explained some of the variance in growth- and reproduction-related traits. No significant correlations were found between the terpenoid functional Hill diversity (FHD) or its components (terpenoid richness, evenness, and structural disparity) and growth- and reproduction-related plant traits. Our results suggest that both the terpenoid chemotype of an individual and the chemodiversity of its neighborhood can impact reproduction-related traits, possibly driven by interactions of the individual with the environment and different resource allocation.

Light pollution is a widespread threat to dark-adapted species. Attraction to artificial light can have severe, even fatal, consequences with population level repercussions, especially for nocturnal insects. Since most insects are particularly drawn to short-wavelength light, the recent switch to LEDs with a greater emission in the blue range has exacerbated the problem. One potential mitigation measure is to adjust light spectra toward longer wavelengths. However, the effectiveness of this measure may vary among species that differ in their spectral sensitivities. In glow-worms (Lampyris noctiluca), nocturnal beetles with presumably declining abundance, especially blue and white artificial light hamper males' search of yellowish-green glowing females. Here, we assessed whether easing the search by switching to longer wavelengths impacts males' phototactic behavior. We recorded the movements of males in an arena illuminated at one end by either white, yellow, red, or no artificial light. Males displayed positive phototaxis toward yellow and red light, and negative phototaxis toward white light, with the latter also being associated with reduced activity. Therefore, males' attraction to longer wavelengths that resemble the female glow could be an evolutionary trap in human-modified environments with artificial lights of that color range. These results show that different wavelengths can influence disparate behaviors even within a single species and adjustment of outdoor lighting systems, by filtering out the blue part of the spectrum, has limited capacity to solve the light pollution problem.

Global climate change and related environmental stress threaten the survival of long-lived tree species. To ensure survival in increasingly unfavorable environments, trees need to either acclimate through phenotypic plasticity, adapt via genetic differentiation, or migrate to more favorable climates altogether. Nonstructural carbohydrate (NSC) storage is a critical trait that supports proper metabolic function in plants and has been shown to prolong their survival in the face of stress. However, relatively few studies have explored local adaptation of NSC storage, with none to our knowledge focusing on oaks, an abundant and ecologically important genus primarily across the Northern Hemisphere. Here, we used a common garden of oak species to assess whether NSC storage is locally adapted by exploring whether species' native range climate influences NSC storage in the stem. We found that the proportion of soluble sugars, the proportion of starch, and starch concentration were influenced by native range temperature, such that species from hotter regions had a larger proportion of soluble sugars, smaller proportion of starch, and lower starch concentration than species from colder regions. These correlations suggest that some NSC traits (i.e., proportion of sugars/starch) are genetically controlled in the genus Quercus. Our study has implications for how different oak species may respond to and survive under environmental stress and changing climates.