Oecologia最新文献

Plant litter is a well-defined pool of organic matter (OM) in which the influence of manganese (Mn) on decomposition (both decomposition rate and the mix of compounds ultimately transferred to soil OM) has been clearly demonstrated in temperate forests. However, no similar study exists on grasslands and the effect of foliar Mn versus soil-derived Mn on litter decomposition is poorly known. We used a 5-month and 12-month field, and 10-month laboratory experiments to evaluate litter decomposition on the Kohala rainfall gradient (Island of Hawai'i) in areas with different foliar and soil Mn abundances, and on which a single plant species (Pennisetum clandestinum) dominates primary production and the litter pool. The chemical imaging analyses of decomposed litter revealed that Mn²⁺ oxidized to Mn³⁺ and Mn⁴⁺ on grass litter during decompositions-hallmarks of Mn-driven litter oxidation. However, these transformations and Mn abundance did not predict greater litter mass loss through decomposition. These observations demonstrate that the importance of Mn to an ecosystem's C cycle does not rely solely on the metal's abundance and availability.

Plants host an array of microbial symbionts, including both bacterial and fungal endophytes located within their roots. While bacterial and fungal endophytes independently alter host plant growth, response to stress and susceptibility to disease, their combined effects on host plants are poorly studied. To tease apart interactions between co-occurring endophytes on plant growth, morphology, physiology, and survival we conducted a greenhouse experiment. Different genotypes of Spartina alterniflora, a foundational salt marsh species, were inoculated with one bacterial endophyte, Kosakonia oryzae, one fungal endophyte, Magnaporthales sp., or co-inoculated. Within the greenhouse, an unplanned herbivory event occurred which allowed insight into the ways bacteria, fungi, and co-inoculation of both endophytic microbes alters plant defense chemicals and changes herbivory. Broadly, the individual inoculation of the bacterial endophyte increased survival, whereas the fungal endophyte increased plant growth traits. Following the herbivory event, the proportion of stems grazed was reduced when plants were inoculated with the individual endophytes and further reduced when both endophytes were present. Across genotypes, anti-herbivore defense chemicals varied by individual and co-inoculation of endophytes. Bacterial inoculation and genotype interactively affected above:below-ground biomass and S. alterniflora survival of ungrazed plants. Overall, our results highlight the variable outcomes of endophyte inoculation on Spartina growth, morphology, phenolics, and survival. This study furthers our understanding of the combined effects of symbionts and plant multitrophic interactions. Further, exploring intra and inter specific effects of plant--microbe symbiosis may be key in better predicting ecosystem level outcomes, particularly in response to global change.

Mutualisms may be more or less sensitive to environmental conditions depending on the diversity and responses of the species involved. Ants frequently form mutualistic associations with plants bearing extrafloral nectaries (EFNs): the ants protect the plants from herbivores and receive food resources (i.e., nectar) in return. As ectotherms, ants are strongly influenced by temperature, and temperature shifts can affect ant-plant interactions in ways that often depend on species functional traits. In this study, we explored the influence of EFN size and leaf surface temperature on ant-plant interactions in a Caatinga dry forest in Brazil. We observed the ants visiting 14 EFN-bearing plant species at different times of day over 12 sampling months; we also measured leaf surface temperatures during these periods. We next quantified EFN size for 68 individuals from the 14 plant species. The observational data were used to characterize the heat tolerance of the attendant ant species (i.e., based on levels of foraging activity). We then evaluated the mutualism's degree of functional resilience using two indices: functional redundancy (i.e., the number of ant species interacting with a given plant species) and thermal response diversity (i.e., variability in the heat tolerance of the ant species interacting with a given plant species). We found that leaf surface temperature, but not EFN size, had an influence on mutualism functional resilience. As temperatures increased, both functional redundancy and thermal response diversity decreased. This result implies that warmer global temperatures could heighten the vulnerability of facultative ant-plant mutualisms, regardless of plant traits.

Understanding how animals navigate novel heterogeneous landscapes is key to predicting species responses to land-use change. Roads are pervasive features of human-altered landscapes, known to alter movement patterns and habitat connectivity of vertebrates like small mammals and amphibians. However, less is known about how roads influence movement of insects, a knowledge gap that is especially glaring in light of recent investments in habitat plantings for insect pollinators along roads verges and medians. In this study, we experimentally investigate behavioral avoidance of roads by a solitary bee and explore whether landscape factors are associated with bee movement in urban Massachusetts, USA. Using mark-recapture surveys, we tracked individual solitary bee (Agapostemon virescens) foraging movements among floral patches separated by roads or grass lawn. We found that roads acted as partial barriers to movements of foraging bees, with road crossings nearly half as likely as along-road movements (36% vs. 64%). Movement probabilities were negatively associated with distance and the proportion of roadway between patches, and positively associated with higher floral resource density at the destination patch. Importantly, our findings also suggest that while roads impede bee movement, they are not complete barriers to dispersal of bees and/or transfer of pollen in urban landscapes. In the context of green space design, our findings suggest that prioritizing contiguous habitat and ensuring higher floral densities along road edges may enhance resource access for pollinators and mitigate the risk of ecological traps.

Soil functional genes in grasslands are crucial for processes like nitrogen fixation, nitrification, denitrification, methane production, and oxidation, integral to nitrogen and methane cycles. However, the impact of global changes on these genes is not well understood. We reviewed 84 studies to examine the effects of nitrogen addition (N), warming (W), increased precipitation (PPT +), decreased precipitation (PPT-), and elevated CO₂ (eCO₂) on these functional genes. For nitrogen cycling, global changes mainly boost genes involved in nitrification but reduce those in denitrification, with nirK being the most sensitive. Most nitrogen fixation-related genes did not show a significant response. Among single factors, N and PPT + have the most significant effects. The impact of global changes on nitrogen cycling genes is largely additive, and their interaction with N is particularly influential. For methane cycling, global changes notably affect mcrA, while only PPT + significantly reduces pmoA. The magnitude and duration of global change treatments are more critical than the treatment form for nitrogen cycling genes. For methane cycling, the form and intensity of nitrogen addition, along with treatment duration, affect pmoA abundance. We also identified a competitive relationship between methane oxidation and nitrification and a complex coupling with denitrification. This study provides new insights into microbial responses in nitrogen and methane cycling under global changes, with significant implications for experimental design and management strategies in grassland ecosystems.

Survival and reproductive success are greatly influenced by how an individual uses its surrounding environment, which can differ across spatial scales. To better understand the habitat-fitness relationships of animals, it is essential to study space use at multiple spatial scales. Here, we used 13 years of capture-mark-recapture and burrow location data to investigate how two different aspects of space use influence the survival and female reproduction in a wild population of eastern chipmunks (Tamias striatus) in southern Québec. We quantified home range size and site fidelity in a population experiencing massive inter-annual variations in food availability due to the masting of American beech trees (Fagus grandifolia). We found that site fidelity tended to increase the probability of reproduction but that this effect was strongly dependent on the context of beech seed production: probability of reproduction was higher for females that were faithful from a mast year to the following non-mast year. Site fidelity was not related to survival and we found no significant effect of home range size on either fitness trait. Our results indicate that, in our study system, different aspects of space use affect fitness traits in different ways. We emphasize the importance of examining multiple spatial scales in related analyses.

This study aims to elucidate the connection between the phylogeny of epiphytic macrolichens and their chemical niches. We analyzed published floristic and environmental data from 90 canopies of Picea glauca x engelmannii across various forest settings in British Columbia. To explore the concordance between a principal coordinates analysis of the cladistic distance matrix and a global non-metric multidimensional scaling of the ecological distance matrix, we used Procrustean randomization tests. The findings uncover a robust association between large-scale macrolichen phylogeny and canopy throughfall chemistry. The high calcium-scores of the studied species effectively distinguished members of the Peltigerales from those of the Lecanorales, although parameters linked with Ca such as Mn, Mg, K, bark-, and soil-pH, may contribute to the niche partitioning along the oligotrophic-mesotrophic gradient. The substantial large-scale phylogenetic variation in the macrolichens' Ca-scores is consistent with an ancient adaptation to specialized chemical environments. Conversely, the minor variation in Ca-scores within families and genera likely stems from more recent adaptation. This study highlights crucial functional and chemical differences between members of the Lecanorales and Peltigerales. The deep phylogenetic connection to the chemical environment underscores the value of lichens as transferable bioindicators for the chemical environment and emphasizes the importance of elucidating the intricate interplay between chemical factors and lichen evolution.

Aquatic pathogens often cannot tolerate drying, and thus their spread, and diversity across a landscape may depend on interactions between hydrological conditions and the movement of infected hosts. The aquatic fungus Batrachochytrium dendrobatidis (Bd) is a nearly ubiquitous pathogen of amphibians and particular lineages have been associated with host declines. By coupling amphibian surveys with molecular pathogen detection and genotyping techniques, we characterized the spatial dynamics and genetic diversity of Bd on a landscape containing both permanent and ephemeral ponds. In doing so, we aimed to clarify how pathogen loads and prevalences vary across seasons and among habitat types, and which host species move the pathogen from place to place. At the start of spring breeding, Bd prevalence was lower on amphibians sampled from ephemeral ponds. For the remainder of the amphibian active season, prevalence was similar across both ephemeral and permanent ponds, with variation in prevalence being well-explained by a hump-shaped relationship with host body temperature. The first amphibians to arrive at these ephemeral ponds infected were species that breed in ephemeral ponds and likely emerged infected from terrestrial hibernacula. However, species from permanent ponds, most of which hibernate aquatically, later visited the ephemeral ponds and these animals had a greater prevalence and load of Bd, suggesting that migrants among ponds and pond types also move Bd across the landscape. The Bd we sampled was genetically diverse within ponds but showed little genetic structure among ponds, host species, or seasons. Taken together, our findings suggest that Bd can be diverse even at small scales and moves readily across a landscape with help from a wide variety of hosts.

Assessing plant-pollinator relationships often employs a snapshot approach to describe the complexity and dynamic involving species interactions. However, this framework overlooks the nuanced changes in species composition, their interactions, and the underlying drivers of such variations. This is particularly evident on less explored temporal scales, such as the dynamic decision-making processes occurring within hours throughout the day. To address these gaps, in this study, we evaluated the temporal and environmental factors shaping the change of species and interactions (beta diversity) between bees and plants throughout the day in a coastal environment in Mexico. In general, we found that the changes in species composition of bees and plants were mainly associated with species turnover throughout the day, while the principal component of changes in interaction composition was interaction rewiring (reassembling of pairwise bee-plant interactions). This was mainly because a few species (6 of 47 bee species, and 5 of 35 plant species) with many interactions remain permanent most of the day, leading to rewiring being the most important component of beta diversity interaction. While environmental conditions such as temperature and humidity did not significantly drive the compositional dissimilarity of species and interactions, we observed that nearby time intervals have a similar composition of species and interactions. In conclusion, our study emphasizes the importance of considering shorter temporal dynamics in understanding species interactions during the day. These insights deepen our understanding of the intricate dynamics shaping plant-pollinator interactions, providing valuable implications for future studies focused on conservation and management strategies.

Global change drivers such as habitat fragmentation, species invasion, and climate warming can act synergistically upon native systems; however, global change drivers can be neutralized if they induce antagonistic interactions in ecological communities. Deadwood comprises a considerable portion of forest carbon, and it functions as refuge, nesting habitat and nutrient source for plant, animal and microbial communities. We predicted that thermophilic termites would increase wood decomposition with experimental warming and in forest edge habitat. Alternately, given that predatory ants also are thermophilic, they might limit termite-mediated decomposition regardless of warming. In addition, we predicted that a non-native, putative termite-specialist ant species would decrease termite activity, and consequently decomposition, when replacing native ants. We tested these hypotheses using experimental warming plots (~ 2.5 °C above ambient) where termites, and their ant predators, have full access and vary in abundance at microscales. We found that termite activity was the strongest control on decomposition of field wood assays, with mass loss increasing 20% with each doubling of termite activity. However, both native and non-native ant abundance increased with experimental warming and, in turn, appeared to equally limit termite activity and, consequently, reduced wood decomposition rates. As a result, experimental warming had little net effect on the decomposition rates-likely because, although termite activity increased somewhat in warmed plots, ant abundances increased more than five times as much. Our results suggest that, in temperate southern U.S. forests, the negative top-down effects of predatory ants on termites outweighed the potential positive influences of warming on termite-driven wood decomposition rates.