Oecologia最新文献

Many plant species are moving to higher elevations due to global warming, but the effects of these elevational shifts on plant-pollinator interactions are not well understood. This study aimed to examine how flower visitation and seed set of lowland plants change after they shift uphill, and whether they compete for pollinators with plants native to the mountains. We conducted an experiment using two plant groups: lowland species pre-planted in a greenhouse and transplanted to both lowland and mountain sites, and mountain species. Pollinators were recorded at lowland sites for planted species and at mountain sites for both planted and native species. We also used pan traps in white, yellow, and blue colours to collect pollinators at both sites. Afterwards, seed sets of the planted species were counted to compare pollination success between elevations. Flower visitation rates on planted species were not significantly affected by elevation, although pollinator abundance in pan traps was higher in the mountains. The pollinator spectrum varied across elevations and plant species, influenced by flower and pan trap colour. However, planted species produced more seeds at lowland sites, indicating higher pollination success there. Overall, we found no evidence of competitive advantage for range-shifting lowland species in terms of pollination.

Pollinator behaviour during floral visits shapes plant mating opportunities, influencing the likelihood of outcrossing versus selfing. These behaviours may be affected by plant responses to antagonists such as insect herbivores. This study aimed to better understand how insect herbivory affects visitation behaviour of two pollinator community members of field mustard (Brassica rapa): the buff-tailed bumblebee (Bombus terrestris) and the large cabbage white butterfly (Pieris brassicae). In field tent experiments, we allowed caterpillars of P. brassicae to develop from leaf-feeding early instars to flower-feeding late instars and assessed pollinator response to undamaged and damaged plants during 10-min observations. We recorded behaviours with potential effect on outcrossing: (first) choice and overall plant preference, plant visit duration, number and duration of flower visits per plant, and distance travelled between plant visits. Bumblebees visited more plants and flowers, but spent less time per flower than butterflies did. Bumblebees often travelled to neighboring plants, whereas butterflies often flew longer distances to reach a next plant. Herbivory by large florivorous caterpillars altered butterfly plant choice-mostly towards plants with caterpillars, but not their behaviour on the plant. Bumblebees did not alter their choices, but changed their behaviour on the plant: they visited more flowers on plants with herbivory. However, herbivory by small leaf-feeding caterpillars did not affect the behaviour of either pollinator. Our results show that pollinator community members respond differently to herbivory and that this response changes over time, potentially affecting plant mating patterns.

Electrical infrastructure networks are predicted to greatly expand in response to the expected 48% increase in global energy demand by 2040. While assessments of electrical infrastructure are abundant, mixed effects on animal diversity have been reported, warranting further evaluation to determine true effects. We conducted a systematic literature review covering individual, population, and community-level assessments to determine the impacts posed to animal biodiversity by electrical infrastructure and the measures to reduce impacts. Our results show that the literature around electrical infrastructure and animal biodiversity has grown exponentially since the start of the millennium and is biased towards birds and mammals in economically developed countries. We found the majority of reported impacts were negative, occurring primarily through barrier effects (collision) and use of linear features as a resource (electrocution), causing significant population impacts in select species. However, we also found that electrical infrastructure provided positive effects (increased habitat provisioning) to certain taxonomic groups (e.g. corvids, storks), which suggests the potential to encourage conservation efforts using appropriate mitigation on electrical infrastructure. We found the majority of current literature detailed mitigation measures focused on reducing collisions through line (51%) and tower alterations (30%), but often omitted the impacts of EMF, noise, and UV, indicating significant knowledge gaps. On a wider scale, we found that mortality from electrical infrastructure ranked lower than building collisions and predation from feral cats, but remained higher than other anthropogenic energy sources, indicating the potential to cause significant impacts to large-bodied bird species if not addressed.

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.