Oecologia最新文献

Invasive species success in novel habitats is shaped by the interplay between propagule pressure and environmental resistance. Although high propagule pressure often drives invasion, establishment can fail when strong resistance limits new recruits. Disturbance may reduce resistance by disrupting resident communities and increasing resource availability especially for fast-growing species. To test the generality of these dynamics, Oxalis stricta L. was used as a model invader and turfgrass assemblages as generalized low-diversity systems common in anthropogenic landscapes. In a controlled glasshouse experiment, O. stricta and manipulated environmental resistance were introduced through variation in plant cover, soil moisture, and nutrients. Despite producing more than 400,000 seeds in 17 weeks, O. stricta was almost entirely excluded from vegetated trays (< 2% cover, no reproduction), whereas cover in bare soil often approached 100%. After colonization, seedpod production plateaued at ~ 75% cover, consistent with negative density dependence. Supplemental watering increased O. stricta growth in bare soil, whereas fertilization had little direct effect but shifted turfgrass competition which further suppressed invasion. These results suggest that even extreme propagule pressure is insufficient to overcome strong environmental resistance. At the same time, the ability of O. stricta to self-pollinate and persist in disturbed microsites indicated that minimal founder populations may still establish under fluctuating conditions.

Cross-system fluxes of aquatic insects rich in omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFAs), specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may subsidise insectivorous vertebrates that are suffering due to terrestrial insect declines. The benefits of high ω-3 LC-PUFA diets, such as improved growth and immunocompetence, have previously been demonstrated for riparian insectivores. Understanding the potential for aquatic insects to benefit a range of species is necessary for informing land management practices. Using the spotted flycatcher (Muscicapa striata), a habitat-generalist, insectivorous bird as a model, we tested how blood plasma ω-3 LC-PUFA concentrations and the ratio of ω-6:ω-3 fatty acids were related to the body condition of 14 adults and 84 chicks in the wild. We measured how variation in ω-3 LC-PUFAs and ω-6:ω-3 was related to river proximity, to test whether they were related to aquatic insect availability. We assessed how these relationships may extend beyond the individual level by monitoring flying insect availability throughout two breeding seasons and testing its ability to predict reproductive success. EPA was positively correlated with body condition in chicks and adults and declined with distance from a river. Conversely, ω-6:ω-3 was negatively correlated with body condition and increased with distance from a river. Breeding success was positively correlated with aquatic insect availability, suggesting that access to a high ω-3 LC-PUFA diet has the potential to mitigate declines in generalist insectivores. Our results highlight how the maintenance or creation of high-quality freshwater habitats may be promoted in a conservation context for non-riparian species.

One of the main causes of poor ecological surface water quality in Europe is nutrient enrichment due to agricultural activities. Riparian buffer zones, the vegetative zones between agricultural land and surface waters, have proven to retain and remove nutrients, yet with highly variable effectivity. So far, the role of invertebrates as an explanation for this variability remains severely overlooked. Therefore, this study aimed to assess the contribution of invertebrates to nutrient retention and removal processes of riparian buffer zones. Only four articles on invertebrate activity in riparian buffer zones were found, which focused on their role in denitrification and nitrate leaching, ignoring the variety of other processes that contribute to buffer zone effectivity. Therefore, knowledge on the role of invertebrates available from other ecosystems was synthesized and extrapolated to riparian buffer zones. It is concluded that the effects of invertebrates on nutrient retention and removal processes often depend on specific species or functional groups, the intensity of bioturbation and feeding activity, as well as on the soil and sediment characteristics. We have made a strong case here that these same invertebrate-environment interactions are also likely to occur in buffer zone ecosystems, mediating nutrient dynamics. To efficiently tackle the most pressing knowledge gaps, the three most important components of future research should be: (1) the quantification of species-specific contribution of invertebrates, (2) the effects of lumbricid communities, and (3) the effects of their large-scale behavior on nutrient dynamics in hydrologically dynamic riparian buffer zones.

Nitrogen (N) and phosphorus (P) allocation strategies are central to plant ecology, yet most studies oversimplify stems by ignoring the functional divergence between bark and wood. In addition, the combination of stoichiometric homeostasis and network analysis to elucidate adaptation strategies between evergreen and deciduous species has rarely been investigated. Here, we measured N and P concentrations across the plant-soil system (leaf, bark, wood, root, and soil) in 75 subtropical woody species (44 evergreen and 31 deciduous). Bark exhibited a lower N vs. P scaling exponent (α = 0.80) compared to wood (α ≈ 1.0). Functionally similar organs (e.g., leaf-bark in photosynthesis, wood-root in transport) showed isometric N and P allocation (α ≈ 1.0), whereas functionally divergent organs (e.g., leaf-root) followed an allometric scaling relationship (α < 1.0), aligning with the functional similarity rule. Compared to deciduous species, evergreen species exhibited greater stoichiometric homeostasis, higher network edge density (0.61 vs. 0.25; indicating stronger resource integration), and reduced modularity (0.09 vs. 0.31; reflecting functional interdependence rather than division). Our findings demonstrate that evergreen and deciduous species adopt divergent strategies through homeostasis and network structure differentiation, and highlight the need to refine ecosystem models by incorporating bark-wood differentiated N-P allocation mechanisms.

Identifying and monitoring the processes underlying changes in individual life-history traits and population size are essential to better predict natural populations' responses to environmental changes and sustainably manage natural resources. In marine ecosystems, the global decline in small pelagic fish (SPF) growth and survival capacities was linked to overfishing and climate change, but the underlying mechanisms remain elusive, although SPF play a central ecological role and sustain large fisheries. To address this issue, we combined a set of physiological markers (assessing digestive enzyme activity, oxidative, chronic, and nutritional stress) and environmental variables for sardine (Sardina pilchardus) in three environmentally contrasted areas surrounding the French coast. Overall, we found sardines with higher chronic stress, lower content in eicosapentaenoic acid (EPA), and lower digestive enzyme activity in the Gulf of Lions, an area marked by a 30% decline in sardine size-at-age and a strong adult overmortality. In contrast, sardines from the English Channel, where no such demographic decline is observed, exhibited better physiological conditions. Sardines appeared to be in poorer physiological health under warmer sea surface temperatures and lower phytoplankton concentrations. However, links between physiology and environmental variability were less clear in the Bay of Biscay, an area with similar growth and survival declines than in the Gulf of Lions. These findings highlight the critical impact of environmental factors on the physiological status and overall health of sardine populations but with global and local patterns of response, emphasizing the unique challenges faced by each population of this species.

Assessing reproductive status and the nutrient allocation strategies animals use to reproduce is integral for evaluating their vulnerability to environmental change; however, the elusive nature of many animals hinders our ability to assess the impact of these vital life history events on homeostasis. We developed a proxy for assessing protein balance in capital-breeding southern right whales (Eubalaena australis) based on carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope analysis of amino acids (AA) in skin biopsy samples (n = 82) collected from free-ranging whales. Most AA in lactating females (cows) had higher δ¹³C but lower δ¹⁵N values in comparison to adult non-lactating females and adult males, suggesting they route fat stores for milk production and use protein reserves to maintain tissues. Lower AA δ¹⁵N values are likely associated with protein sparing and/or modifications to the urea cycle to retain or recycle nitrogen during reproduction. Nursing calves had distinctive AA δ¹³C and δ¹⁵N patterns compared to cows and adults, likely driven by the acquisition of protein from milk and the use of maternal resources in utero to support the high metabolic demands associated with rapid growth. Adult males and non-lactating adult females had nearly identical AA δ¹³C and δ¹⁵N patterns, suggesting they use similar nutrient allocation strategies while fasting. Patterns in δ¹³C and δ¹⁵N values among AA yielded correct classification of demographic groups with 98% accuracy and identification of lactating cows with 100% accuracy, showing that this new method holds promise for identifying the reproductive status of capital breeding mammals.

When foraging optimally, mammalian herbivores should select food items that confer the greatest nutritional benefits (e.g., crude protein and non-structural carbohydrates) and impose minimal-to-no costs (e.g., plant secondary metabolites [PSMs]). PSMs, such as tannins, deter herbivores by providing post-ingestive feedback cues that the forager experiences after consumption, and are therefore difficult for herbivores to avoid altogether. However, some PSMs, such as terpenes, are also volatile organic compounds (VOCs) that become gaseous at ambient temperatures and can be detected by herbivores via scent prior to ingestion. Our objective was to discern if the foraging preferences of white-tailed deer, a near ubiquitous herbivore in North America, were influenced by the nutritional or anti-nutritional constituents of trees during summer and winter. We also examined VOCs emitted by trees during summer and tested for a potential relationship between VOC emissions and deer sniffing behavior or foraging preference. During summer, deer preferred trees with a high non-structural carbohydrate content. After sniffing trees that emitted a large proportion of terpenes, deer appeared to be averse to begin foraging. During winter, deer preferred trees with a low crude protein content and a high tannin content. When deer foraged from trees with high terpene contents, they consumed less than they did from low terpene trees. Our results show that white-tailed deer foraging behavior is influenced by plant nutritional constituents. Additionally, we suggest that differences in VOCs among tree species may provide deer with cues of plant quality that could play a role when selecting forage items.

Releasing captive-reared animals into the wild is a common population management practise, but their inexperience with predators often leads to high post-release mortality. Although captive animals can be trained to recognize and respond to predatory cues, the post-release survival benefits of this method remain uncertain. Additionally, how factors related to captive breeding and rearing-such as hybridization and disease, which can affect learning and memory-influence the effectiveness of antipredator training has not been investigated. We conducted two experiments with Atlantic salmon (Salmo salar), during which they first underwent antipredator training via paired exposure to predator cues (Northern pike, Esox lucius) and conspecific alarm cues, followed by release into semi-natural streams for predation trials with live pike. The first experiment focused on post-release behaviours and demonstrated innate predator avoidance that was not enhanced by the training. In the second experiment, genetic background (purebred versus hybrid crosses) and parasite infection status (trematode eye fluke, Diplostomum pseudospathaceum) of the salmon were manipulated to assess their effects on antipredator learning. This experiment demonstrated a clear survival benefit from the training, which was not influenced by either the genetic background or infection. The variation in effectiveness of the antipredator training between the experiments may be attributed to different experimental environments and developmental stages of the salmon. Overall, our findings suggest that antipredator training conducted under specific conditions enhances post-release survival of captive-reared salmon, providing valuable insights for reintroduction and population augmentation programmes.

Sexual selection due to mate preference for certain traits can maintain phenotypic diversity within populations and species. In taxa with discrete phenotypes, such as color polymorphic species, assortative mating may lead to disruptive selection and sympatric divergence, yet how such interactions vary over species' ranges remains poorly understood. To address this shortcoming, we examined spatial patterns of sexual size dimorphism and presumptive male-female mating pairs based on body size and coloration in the color polymorphic Eastern Red-backed Salamander, Plethodon cinereus. This species exhibits two common color morphs, striped and unstriped, that also differ in other elements of their biology, including ecology, behavior, and morphology. Across six populations that vary in color morph frequency, we predicted each site would show female-biased sexual size dimorphism and a positive body size relationship between presumptive mating pairs. In polymorphic sites, we also predicted that morphs would demonstrate color-based assortative mating, with larger body size as an associated trait. We found female-biased sexual size dimorphism in three of six study sites, while a positive body size relationship between male and female pairs was documented in four populations, and no evidence of male-female associations by color and body size was found in polymorphic populations. The spatial variation across all of our study axes demonstrates the importance of geographic context in shaping sexual selection dynamics and patterns of local adaptation.

Despite the prevalence of both Harmonia axyridis and its fungal ectoparasite Hesperomyces harmoniae across the globe, few studies have explored the impact of Hesperomyces harmoniae on the immune system and thermal performance of Harmonia axyridis, both of which are important traits for the continued geographic range expansion of this invasive species. Since He. harmoniae does impose a cost on Ha. axyridis (overwintering survival), we predicted that infected ladybirds collected from the field would have an increased immune response and decreased phenotypic performance compared to uninfected ladybirds. Moreover, these effects would depend on the season in which ladybirds were collected (summer growing vs autumn pre-overwintering season). In general, collection season had a significant effect on all physiological traits we assayed. All hemolymph parameters significantly decreased from summer to autumn. Ladybird movement activity and range of utilized temperatures increased from summer to autumn, whereas, average preferred temperature decreased from summer to autumn. Unsurprisingly, summer ladybirds were more heat tolerant and autumn ladybirds were more cold tolerant. He. harmoniae infection had almost no impact on any of the investigated traits. The only exception to this was with respect to cold tolerance, He. harmoniae infected ladybirds being less cold tolerant than uninfected ladybirds. Therefore, infection by this fungus does not appear to be physiologically severe enough to elicit a whole-body negative effect on its host ladybird, but instead, may deplete specific internal resources that negatively impact cold tolerance.