Oecologia最新文献

Animal gut microbiomes, particularly those of herbivorous mammals, are strongly shaped by the host diet. However, how dietary composition impacts gut microbiome variation across a population of wild hosts is unknown. To examine the relationship between gut microbiome composition and diet composition across individuals, we employed a multi-omic approach leveraging both 16S rRNA amplicon sequencing and plant DNA metabarcoding (tRNL primer) in 39 wild yellow-bellied marmot fecal samples from the Rocky Mountains. We utilized the 16 s rRNA primer to target microbes and the tRNL primer to target plants. Our results indicate that the marmot gut microbiomes appear to be stable against dietary variation, even across individuals with significantly different diets. We also show that colony membership significantly impacts marmot dietary variation, while age does not. Thus, while diet clearly plays a significant role in shaping mammalian gut microbiomes, our study suggests that diet composition within the same species has a minimal impact on gut microbiome variation, particularly in the absence of experimental manipulations and dietary interventions.

Increasing rainfall deficits threaten the persistence of terrestrial large herbivores, yet, very few studies have investigated the effects of droughts on populations inhabiting anthropized areas, which dominate European landscapes. We investigated how rainfall deficits (measured using the Standardized Precipitation Index, SPI) and local agricultural land use shaped the early growth of fawns and the body mass that they attained by their first winter in a population of European roe deer (Capreolus capreolus) in southwestern France. Using data on 155 new-born fawns, we found that early growth decreased as local woodland availability increased, irrespective of spring rainfall conditions. In contrast, based on data from 218 GPS-monitored juveniles, aged 8-10 months, we found that local landscape composition and seasonal rainfall deficits had interacting effects on winter body mass. The juveniles were generally heavier with higher proportions of meadows in their predicted home range (mean 0.4 kg ± 0.2 SE), but this difference disappeared following dry summers (SPI < 1). Juveniles with low access to summer crops (e.g., 5%) were significantly lighter following dry autumns (mean -0.9 kg ± 0.3 SE), whereas this was not the case for those with higher access to these crops (e.g., 20%). Although populations of large herbivores may respond to harsh climatic conditions by exploiting anthropogenic resources, our results suggest that any compensation effects are strongly dependent on the type of anthropogenic land use and the timing of rainfall deficits, calling for explicitly considering how local climatic conditions and human practices may interact in shaping individual performance and, so, population dynamics.

The nonconsumptive effects associated with the predator-avoidance behaviors of potential prey species may commonly be context-dependent. In this study, we examined how temperature differences between the phyllosphere and the ground change the consequences of predator-avoidance dropping behavior in monarch caterpillars. We hypothesized that these consequences change on both diel and seasonal timescales, and that the risk associated with exposure to potentially high ground temperatures is likely to be greater for smaller caterpillars that have less thermal inertia and movement ability. We conducted field experiments to assess the mortality risk associated with dropping to the ground for different-sized caterpillars at a wide range of ground temperatures. We also assess if a caterpillar's probability of dropping in response to a standardized, simulated attack is consistent with adaptive expectations given variation in observed mortality risk under different conditions. We found that the survivorship consequences of dropping depend on both temperature and caterpillar size and that monarch caterpillars show context-dependent predator-avoidance behaviors consistent with changing adaptive expectations across a wide range of temperatures and body sizes. However, we also observed a potentially nonadaptive willingness to drop at high temperatures, consistent with a biological constraint imposed by increased reactivity. These results contribute to a general knowledge gap regarding the context dependence of nonconsumptive effects in nature.

Natal philopatry, the practice of a mother reproducing in the same region as her natal site, has been documented in numerous species. Studies on marine mammal philopatry have primarily focused on cross-colony scales, leaving a knowledge gap for fine-scale philopatry within colonies. We sought to identify the rate of fine-scale natal philopatry in northern elephant seals, sustained site fidelity across years, and additional drivers of site selection during the breeding season. Using 20 years of mark-recapture data collected from the ~3200-m long Año Nuevo colony in northern California, we discovered high rates of fine-scale philopatry, with females pupping an average of 395 m from where they were born. Females producing pups showed high site fidelity to the site of their first pup production, although the correlation was not as strong as to their natal site. Our results have implications for within-colony genetic connectivity and generational shifts in breeding sites influenced by coastal erosion.

Studying latitudinal cline in life-history traits is crucial for understanding how organisms adapt to seasonal environments and for predicting their potential responses to ongoing climate change. In this study, we systematically examined the life-history traits of the cabbage beetle Colaphellus bowringi collected from six sites spanning a 21° latitudinal range. Our results demonstrated that post-diapause female body weight and fecundity decreased in a stepwise manner with increasing latitude, consistent with the converse Bergmann's rule. This pattern was also found in pupal and adult weight of their offspring. Larval development time increased while growth rate decreased in a stepwise manner with increasing latitude, indicating cogradient variation. We further found that these stepwise changes are associated with voltinism. Specifically, multivoltine populations exhibited one set of life-history trait pattern, bivoltine populations another, and univoltine populations yet another, collectively forming a stepwise pattern. Additionally, male pupae experienced significantly greater weight loss during metamorphosis compared to female pupae, resulting in lower sexual size dimorphism (SSD) in pupae than in adults. This suggests that sex-specific weight loss during metamorphosis mediates SSD. In summary, our study provides a comprehensive example of insect life-history evolution, particularly in the empirical study of stepped variation patterns. These findings enhance our understanding of latitudinal variation in life-history traits.

Nonlinear dynamics govern ecological processes; thus, understanding thresholds is important for measuring and forecasting the effects of climate change and management of natural resources. However, identifying whether and how such thresholds transfer across ecological levels of organization remains challenging. We argue for a broadening of a foundational organismal concept from ecological stoichiometry theory, the threshold elemental ratio (TER), to study how nonlinear dynamics driven by shifts in limitation operate in evolutionary and ecological processes from organisms to ecosystems. Traditionally, TERs are used to describe the elemental ratio at which the limitation of organismal growth shifts from one element to another. Building on this definition, we make a case for broadening the TER beyond organisms to include populations, clades, communities, and ecosystems. We discuss how TERs may be detected and translated across different ecological levels and evolutionary processes through simulation modeling, literature review, and synthesis of empirical examples from diverse systems and scales including: cyanotoxin production in lakes, alder-salmon dynamics, and the Cambrian explosion. Collectively, we argue that TERs are likely widespread and consequential across levels of ecological organization and that such thresholds manifest from a diversity of mechanisms. Thus, applying the TER concept across ecological levels of organization holds promise for advancing our understanding of nonlinear dynamics from the micro-evolutionary to the macro-ecological.

The analysis of stable isotopes of carbon and nitrogen is widely used in ecological investigations. However, sources of variation in isotope ratios of animals are far from being identified, which may bias the interpretation of the results. It has been suggested that stress is a factor that affects isotope ratios and trophic enrichment in animal bodies. Here, we tested the hypothesis that stress due to exposure to a predation threat affects metabolic processes that ultimately result in altered isotope composition of threatened prey. We found that both the nitrogen isotope composition (δ¹⁵N) and trophic enrichment in ¹⁵N isotope (Δ¹⁵N) were affected by threat induced by planktivorous fish in two species of the keystone freshwater pelagic herbivore Daphnia: D. magna and D. pulex. The two species differed from each other with regard to isotope ratios. Despite this, with increasing perceived risk of predation, the δ¹⁵N decreased in both species and, as a consequence, individuals of the two species were depleted in ¹⁵N with respect to their conspecifics not exposed to predation. We have not found evidence that the carbon isotope ratio (δ¹³C) was affected by the predation threat. The eco-physiological responses underlying the induction of antipredatory defences may be responsible for the observed pattern. The effect of predation on the nitrogen isotope ratio (δ¹⁵N and Δ¹⁵N) of consumers should be accounted for when using the analysis of stable isotopes in ecological investigations. Moreover, it could be applied to the fossil record to identify the introduction or removal of planktivorous predators in the paleoenvironment.

The larvae of unionid mussels are obligate parasites. Their survival and metamorphosis into juvenile mussels depend on attaching to physically suitable hosts. Although unionid mussels are important ecosystem engineers, the effects of their shells on the host fish species remain poorly understood. The unionid species, Pronodularia japanensis, uses freshwater gobies (Rhinogobius) as hosts for its larvae. In this study, we conducted microcosm experiments under predation risk from a carnivorous fish, the Korean perch (Coreoperca herzi), to assess whether empty shells of unionid mussels could provide anti-predator refuges for gobies. Additionally, we examined whether shells of the Asian clam (Corbicula) could serve as alternative refuges to the unionid shells. The presence of unionid shells substantially enhanced goby survival after a 48-h predation period, whereas Asian clam shells had no such effect. Video recordings revealed that gobies hid beneath unionid shells but not beneath Asian clam shells. Our findings indicate that the shells of deceased unionids can positively influence potential host fish, suggesting a mutualistic relationship between unionids and host fish mediated through shell-derived refuge effects. Furthermore, our results suggest that replacing unionids with non-native Asian clams in natural habitats may negatively affect host fish populations.

Anthropogenic activities cause the accumulation of biologically reactive nitrogen in ecosystems worldwide, leading to substantial changes in plant community structure and function, particularly in nitrogen-limited grasslands. Responses of plant communities and primary productivity vary depending on the magnitude of eutrophication and climate of the ecosystem, yet the exact form of these relationships is largely unknown. Here, we report results from the first 5 years of an experiment in which nitrogen was added at eight levels, ranging from 0 to 30 g m^-2 at two grassland sites bookending the broad precipitation gradient of the US Central Plains: (1) semi-arid shortgrass steppe and (2) mesic tallgrass prairie. This allowed us to examine the mediating effects of climate on short-term aboveground net primary productivity (ANPP) and plant community responses to nitrogen addition. Although nitrogen addition caused a decrease in plant species richness at both grassland sites, the two sites differed in their responses in ANPP and plant composition. At the shortgrass site, we found no effect of nitrogen addition at any level on ANPP, but compositional change occurred starting at 5 g m^-2. In contrast, ANPP at the tallgrass site increased at 5 g m^-2 then saturated, but no significant compositional change was observed. Collectively, these results provide two key insights: (1) ANPP and plant community responses can be decoupled with short-term nitrogen addition and (2) site-level water limitation can result in contrasting responses of grasslands to 5 years of nitrogen addition, but with these effects manifesting at the same critical load of addition.

Petiole mechanics is essential for displaying leaf lamina efficiently in a shaded forest understory. We investigated the structure, anatomy, and mechanics of the petioles of 25 coexisting woody species in a warm-temperate forest understory and related them to interspecific differences in leaf size, habit (evergreen vs deciduous leaves), and form (simple vs compound leaves). Flexural stiffness of the petioles was greater in large leaves than in small leaves, in evergreen leaves than in deciduous leaves of similar area, and in compound leaves than in simple leaves of similar area. Greater second-order moment of area of petioles was responsible for greater flexural stiffness for species with large leaves and evergreen species. In contrast, the petioles of compound leaves showed a greater modulus of elasticity, but a smaller second-order moment of area compared to those of simple leaves of similar leaf area. Anatomical properties were related to the flexural stiffness and resulted in different biomass costs of the petioles. These results are consistent with the idea that the petioles of compound leaves are analogous to laterally growing branches, in which the increase in density is theoretically efficient in terms of the mass required to produce a branch of a given length. Therefore, different factors constrained the flexural stiffness of petioles among coexisting species of different leaf groups.