Oecologia最新文献

Pulses of plant resources can influence the spatial aggregation and population dynamics of primary consumers, but the extent to which these effects cascade up the food chain to affect secondary consumers remains poorly understood. Mast fruiting events in Southeast Asian dipterocarp forests, for example, are known to impact a wide range of bird and mammal granivores, but it remains unclear whether the predators of these vertebrates are indirectly affected by seed production. Here, we assess bottom-up effects of masting on a suite of primary and secondary consumers in a tropical rainforest in Borneo, using structural equation models to characterize a network of frugivore/granivores and carnivores. The models were parameterized using 10 years of camera trap and seed availability data collected between 2013 and 2024, spanning two major masting events. These models also account for an outbreak of introduced disease (African swine fever) and the reduced abundance of human visitors in the forest during the COVID-19 pandemic. Dipterocarp seed availability was correlated with the intensity of local site use by omnivorous Malay civets (Viverra tangalunga) and bearded pigs (Sus barbatus), but not granivorous murid rodents or pheasants. Leopard cat site use was correlated with murid rodents, but not pheasants. These findings suggest that masting in this ecosystem is associated with site use intensity of some large-bodied primary consumers but not smaller granivores, and therefore did not percolate up the food web to influence the predators of these taxa, in contrast to research from temperate masting systems.

Human-induced changes in nitrogen (N) and phosphorus (P) global cycles and availability significantly impact plant growth and nutritional composition, thereby affecting ecosystem dynamics. However, research on the effects of increased nutrient availability often focuses on plant community-level effects, overlooking interspecific variability and neglecting impacts on higher trophic levels. Using a controlled fertilization experiment with six tree species that naturally occur in the Cerrado biome (Brazilian savannas), we showed that there is substantial interspecific variation in how plants respond to nutrient changes. This reflects the existence of competitive advantage for certain native species under a scenario of increased soil nutrient availability. Such effects propagated to higher trophic levels (herbivores and their predators), also varying between plant host species. The strength and direction of N input effect depended on P levels and the type of herbivores. Large invertebrate leaf herbivores were less affected than phytophagous mites. Impacts on higher trophic levels (predatory mites) were less pronounced than on phytophagous mites. Overall, we show that ongoing soil nutrient enrichment has the potential to alter interspecific competition dynamics in plant communities with consequences for ecological interaction partners. These findings have important implications for conservation and ecosystem management, especially in areas highly exposed to soil nutrient enrichment due to farming and industrial activities.

Understanding the influence of species interactions on community structure and biodiversity is a long-standing goal in ecology. While species interactions are predicted to be vulnerable to environmental change, how the environment influences species interactions is not well understood. We used a network analysis approach to examine how network structure and dissimilarity of one type of mixed-species animal group, army ant-following birds, varied along rainfall and habitat suitability (i.e., fragmentation) gradients in Panama. Network structure varied across both gradients and there was high interaction dissimilarity across networks, owing to both species turnover and rewiring. These results highlight the role of the environment in structuring species interactions. Importantly, there was total dissolution of ant-following groups at sites with lower habitat suitability. In drier sites, networks were more speciose, cohesive, and well-connected compared to wetter forests, potentially because of the increased benefits of attending swarms in drier sites. The high cohesion and connections found suggest that ant-following birds may be particularly vulnerable to the loss of important species and environmental change. These ant swarms are an important, shared food resource that draws together a diverse and tightly connected group of birds. Understanding the relationships between the environment and species interactions contributes to our ability to predict how species interactions will change in the future, with cascading effects on community structure and biodiversity.

Nitrogen enrichment leads to diversity loss of plant community in grasslands, and it typically enhances productivity in short-term scale but decreases it in the long term. Short-term negative N effect on stability has generally been primarily attributed to species synchrony rather than species loss. However, the persistent species loss caused by long-term N enrichment may result in high population variability, ultimately contributing to variability in community productivity. Here, we report results of a 19 year-long experiment that manipulated livestock exclusion and N enrichment in an alpine grassland to test their effects on species richness and stability of aboveground productivity through the years. Results demonstrated that the stability of aboveground productivity declined during the first non-overlapping 5 year window which was primarily driven by increased species synchrony. In the second non-overlapping time window, decrease in stability was largely driven by compounded effects of persistent synchrony and amplified dominant species variability. In the third and fourth non-overlapping 5 year windows, functional diversity loss and subordinate species variability contributed to a continued decline in stability. Mechanistically, the losses of species and functional diversity under different N forms shaped temporal patterns of synchrony and population variability, explaining decrease in stability. These findings reveal a time-dependent destabilization cascade, i.e., initial synchrony-driven fluctuations evolved into a dual effect of synchrony and dominant species variability, ultimately disrupted by population variability. We posit that diversity help to sustains grassland functioning not only  by increasing productivity, but also by maintaining a dynamic balance between synchrony and population variability. This highlights the necessity of conserving plant diversity to secure ecosystem functioning under global change.

The megaherbivore concept suggests that mammals >1000 kg are insensitive to predation as adults. Consequently, their space use should be largely driven by resources. This does not account for the fact that megaherbivores have been hunted by humans for >100,000 years and likely evolved innate responses against human predation. Recent studies indeed show that megaherbivores, such as elephants and rhino, strongly respond to human voices. Few, however, have examined the relative influence of resource versus human risk drivers on the landscape use of megaherbivores. Using a long-term dataset from aerial rhino surveys and poaching events in Hluhluwe-iMfolozi Park, South Africa, we investigated how resource and human risk factors shape the landscape distribution of white rhinoceros (Ceratotherium simum). We used rainfall, fire, catena position, and terrain ruggedness as resource drivers and poaching intensity, and distance to human sound-generating infrastructure as human risk drivers. Both resource and human risk drivers affected rhino landscape distribution. Rhino preferred valley bottoms over midlands and uplands, and the use of the latter two habitats increased during the dry season. During drier wet seasons, rhinos increased their upland habitat use. Rhino avoided the park's fenceline and other infrastructure (roads and camps). Poaching intensity did not influence rhino landscape use. Avoidance of human infrastructures may reduce the effective size of protected areas for rhino. Future work should assess how rhino respond to resources and risk over shorter timescales. Our findings encourage a re-evaluation of the megaherbivore concept to include humans as drivers of their ecology.

The thermal landscape is a key driver of habitat selection by ectotherms, which must optimize body temperatures with other life history requirements such as prey acquisition, predator avoidance, mate searching, and reproduction. For snakes in temperate regions, the thermal consequences of varying habitat use will have profound effects. The detailed study of the summer migration of northern western rattlesnakes (Crotalus oreganus) away from their winter hibernacula has revealed striking differences between individuals and populations in habitat use that ranges from low-elevation grasslands to higher elevation forests. We investigated the implications of this different summer habitat 'choice' on the thermoregulation, thermoregulatory behaviour, and body condition of individuals in southern British Columbia, Canada. Using data from 30 telemetered male snakes carrying implanted thermologgers at multiple study sites, we determined that snakes that remained in lower elevation grassland (open) habitats faced overall fewer thermoregulatory constraints (higher average body temperature, more accurate thermoregulation) than individuals that migrated relatively greater distances into forests. However, despite this cost of forest habitat use, snakes that migrated into forests exhibited significantly better end-of-season body condition and gained proportionally more weight over the active season than snakes remaining in open habitats. Our findings reveal a complex interplay of costs and benefits that individual snakes experience according to the habitat in which they base themselves during the short northern summer.

In seasonal environments climatic variability shapes the timing, duration, and magnitude of primary production with effects that may percolate upward through food chains. While the role of spring phenology and implications of trophic mismatches have been documented in some bird species, including waterfowl, there is little research on the role of growing season duration or overall productivity. Duck species breeding in the western boreal forest (WBF) of North America vary widely in their average timing and plasticity for breeding dates, which may set up differing sensitivity to spring phenology. In contrast, increases in growing season duration and productivity may positively impact species regardless of life history through the extension of the breeding season and bottom-up trophic enrichment. We tested these hypotheses using breeding population estimates for 8 species (or species groups) of ducks and normalized difference vegetation index to infer spring phenology, length of growing season, and growing season productivity for duck survey areas in the WBF, 1982-2019. Spring phenology had mixed effects on species' population growth rates, and effects were generally not consistent with mediation by average breeding dates or plasticity. Length of season and productivity effects showed some species' population growth rates decreasing following longer seasons or higher productivity, opposite our predictions. These results suggest that, for secondary consumers like ducks, the role of growing season characteristics may be mediated or superseded by more complex biotic and abiotic interactions than can be explained with simple annual summaries of growing season characteristics.

Accurate interpretation of an organism's isotopic composition relies heavily on the assumption of steady state, which is often violated owing to limited appreciation for isotope incorporation. We present amino acid (AA) nitrogen isotope (δ¹⁵N) records from the tail hair of an African elephant (Loxodonta africana) that frequently migrated between the Samburu National Wildlife Reserve and Mount Kenya-these regions have drastically different baseline δ¹⁵N values of ~ 10‰. We used this baseline isotopic variation to estimate ¹⁵N incorporation for 13 AAs. We observe that incorporation in most AAs is best described by a two-pool reaction progress variable. Amino acids closely connected with metabolic nitrogen cycling that have higher rates of trans- and deamination, often termed 'trophic AAs', exhibited higher contributions from a short pool (41-75%) with faster incorporation (T₅₀ = 5-37 days). Conversely, AAs associated with lower rates of trans- and deamination, often termed 'source AAs', exhibited higher contributions from a long pool (50-64%) with slower incorporation (T₅₀ > 365 days). Calculation of relative trophic position using glutamic acid and phenylalanine revealed high variabslitty across the time series (TP = 0.3-3.2), suggesting a decoupling of isotopic steady state between AAs as the individual moved among ecosystems with inherently different δ¹⁵N baselines. Failure to consider that incorporation varies across AAs associated with different degrees of nitrogen mobilization has broad implications for trophic position estimates using AA δ¹⁵N values and could lead to erroneous interpretation across ecological systems.

Species coexistence is shaped by how individuals share limiting resources such as space, food, and shelter. Theory predicts that niche differentiation promotes coexistence, depending on habitat characteristics, behavioral traits, and the intensity of competition. Niche use may vary across life stages, as ontogenetic shifts alter habitat use and species interactions. We investigated habitat segregation, niche overlap, and the role of non-crop vegetation in affecting coccinellid coexistence across life stages through semi-controlled experiments and field sampling at 42 sites. Species showed consistent differences in habitat and microhabitat use across developmental stages, influenced by innate behaviors and plastic responses to interspecific interactions. Superior competitors (Hippodamia convergens and Harmonia axyridis) generally dominated prey-rich crop areas during egg, larval, and adult stages, but shifted to sheltered sites outside the plants during pupation. In contrast, Eriopis connexa used soil microhabitats throughout its life cycle, reducing niche overlap with other species. Cycloneda sanguinea, a competitively inferior species, persisted by exploiting non-crop plants, which increased spatial heterogeneity and resource availability. Non-crop vegetation thus promoted coexistence by enabling spatial segregation and reducing presumed competitive asymmetries across life stages. These patterns highlight how the strength of species interactions and spatial partitioning changes ontogenetically, reflecting both behavioral flexibility and the influence of habitat features. We propose a plastic functional classification of species based on their behavioral responses to potential competition-risk scenarios across life stages, ranging from risk-tolerant generalists to conditional risk-avoiders and niche-fidelity strategists, that could be broadened and adapted to other study systems.