Ecosphere最新文献

Changes in the seasonal environment substantially influence organisms. Understanding how species respond to such changes, such as in their feeding interactions and physiology, is key to predicting their resilience to both seasonal and longer term climate changes. The Sitka Sound in Southeast Alaska, USA, is an attractive natural laboratory for studying change, as the marine environment experiences substantial seasonal fluctuations in parameters such as temperature, pH, and productivity between summer and winter. By sampling a suite of dominant macrophyte algae and their benthic herbivores in winter (January) and summer (July) 2019, we investigated how producers and their primary consumers may respond to seasonal change inferred through fatty acid trophic markers. We used a fatty acid logratio selection and analysis approach to ask the following: (1) Do fatty acid biomarkers for algae differ between seasons? (2) Do the same fatty acid biomarkers differ between seasons when applied to herbivores, with herbivore fatty acids tracking the presumed trophic resources? (3) Do fatty acid biomarkers for herbivores differ between seasons, when considered independently from algae? Comparing logratio sets selected each for the algae and the herbivore fatty acids, we found that algae fatty acids were different between our sampling seasons, but the algae-selected fatty acid logratios did not clearly separate most herbivores by season. In contrast, the herbivore-selected logratios strongly distinguished herbivore species between the January and June samplings. Further, dispersions of fatty acid logratios were greater within herbivore species in the winter than in the summer, potentially due to the utilization of more diverse resources when preferred algae are less abundant. In total, results suggest that herbivores are not simply tracking the seasonal fatty acid changes in the dominant algae as trophic resources; instead, herbivore fatty acid seasonal changes may occur largely through some other nonexclusive mechanisms, such as omnivory, reductions or shifts in dietary composition, and/or endogenous physiological responses. Thus, the benthic herbivores in our study appear not to be locked into their diets when faced with seasonal change and may use a range of strategies, including diet diversification, to cope with environmental variation.

As the demand for wind energy development increases across much of the Great Plains region, there is a need to understand how this type of energy generation may impact wildlife. Due to their extensive range across areas with high wind resources, plains sharp-tailed grouse (Tympanuchus phasianellus jamesiTympanuchus phasianellus jamesi) represent a valuable species to evaluate how selection and survival are associated with existing wind energy infrastructure. We used spatial and demographic data collected from radio-marked female sharp-tailed grouse to evaluate resource selection (nest, brood-rearing, and breeding season) and survival (nest and female) near existing wind energy infrastructure during the April to August breeding season over a 3-year period from 2020 to 2022 in northeastern South Dakota, USA. We monitored 119 GPS-marked females captured at eight leks over the study period. We did not find evidence that females selected nest sites in relation to wind energy infrastructure but found that females with broods and females during the breeding season (April–August) avoided areas near high densities of wind turbines within 1.0 and 5.0 km of their home range, respectively. We found consistent selection for lower lengths of transmission lines across all life stages at the home range scale. We did not detect an effect of wind energy infrastructure on nest or female survival. Based on the results of our study, limiting the siting (the process of selecting the optimal location for a project and the associated features) of wind turbines within 5.0 km of sharp-tailed grouse breeding habitat may represent an important siting tool to minimize avoidance of otherwise suitable habitats.

The vertical gradient of light in closed-canopy forests selects for trees with different adult statures, but our understanding of how stature affects forest diversity and demography is unclear. In a species-rich rainforest in Cameroon, we quantified the contributions of four growth forms of increasing adult stature (treelet, understory, canopy, emergent species) to forest structure and diversity, and investigated variation in life history trade-offs across growth forms. Treelets had the highest stem density, contributed the most to forest diversity, and diverged from larger statured species in terms of demographic trade-offs. Growth rates were slower for smaller statured than for larger statured species, and at the adult stage, treelets had significantly lower mortality than other growth forms. We observed significant interspecific trade-off relationships between staure and demographic rates that often differed between growth forms. Recruitment rate strongly declined with adult stature for all growth forms, but recruitment per reproductive adult declined only for emergents. While we observed a significant growth-mortality trade-off across all species, the trade-off was similar across growth forms. Smaller statured species in our study are not light-demanding but rather treelet and understory species that live entirely in the shaded understory. Differences in how historical biogeography has shaped species pools may ultimately cause variation in how adult stature contributes to tropical forest diversity.

Efficient foraging plays a critical role in fitness, yet food choices and underlying nutritional goals vary among animals. To understand those choices and therefore the importance of different food resources, many studies estimate food preferences by applying electivity indices that account for resource availabilities. However, the general applicability of electivity indices in biologically relevant foraging scenarios is unclear. Our major aims were to find effective methods to estimate animals' food choices and to investigate long-term food choices and underlying nutritional goals of the red colobus monkey (Piliocolobus tephrosceles) in Kibale National Park, Uganda, an endangered folivore. We used simulations of different foraging conditions to evaluate the applicability of electivity indices in biologically relevant scenarios to help interpret our results. Then, we used long-term data collected between 2006 and 2016 on the feeding behavior and ecology of red colobus to determine the consumption frequencies of different foods and their food preferences. Based on these results and nutritional concentrations of young leaves of frequently consumed tree species, we investigated the importance of the protein-to-fiber ratio in their diet. Our simulations highlight limitations of electivity indices in biologically relevant foraging scenarios. Further, red colobus clearly chose young leaves over other plant parts, and, considering species and plant part, red colobus fed on many different items, but few dominated their diet. The availability and spatial distribution varied across the most consumed foods, but red colobus preferences remained mostly stable over time. Protein-to-fiber ratio had no association with preference but with consumption frequencies of different young leaves. The limitations of electivity indices in different foraging conditions underline the importance of comparing food preferences with consumption frequencies to assess the importance of different food resources. Our results provide a robust understanding of the food choices and nutritional goals of a leaf-eating animal that can ultimately be used for implementing more effective conservation measures by directing habitat protection or restoration efforts toward these resources.

Bats are acknowledged as suppliers of essential ecosystem services such as insect pest control in agroecosystems. Little is known, however, on how bat assemblages respond to the gradients imposed by anthropogenic landscapes and farming practices and how these environmental effects translate into changes in bat foraging. In this study, we use cider apple crop in northern Spain as a model to address the filtering effects of landscape composition and orchard management on, simultaneously, quantitative and qualitative characteristics of bat local assemblages and their foraging activity. For that, we carried out acoustic monitoring of bats and sampled pest moth abundance across a wider range of apple orchards covering different landscape contexts and local management conditions. We found that bat assemblages markedly varied across orchards, according mostly to landscape composition gradients but with contrasting landscape effects on different assemblage characteristics. Namely, higher levels of rural urbanization and lower cover of seminatural woody habitats around orchards promoted bat total activity and the number of bat species/species complexes. However, this also altered bat assemblage composition, increasing dominance by the most abundant species, and decreased bat functional diversity. Additionally, a greater cover of apple tree canopy within the orchards decreased bat total activity. Landscape gradients led into predictable variations of bat foraging activity, suggesting a potential persistence of pest control services even in landscapes with limited seminatural habitat cover. The present study highlights the differential responses of bat assemblages to apple crop landscape and orchard-scale conditions, hindering the establishment of straightforward management guidelines. Further analysis on the relationship between bat assemblage characteristics and pest control is necessary to understand how ecosystem services can be promoted through management in the apple agroecosystem.

Coastal ecosystems are at the nexus of many high priority challenges in environmental sciences, including predicting the influences of compounding disturbances exacerbated by climate change on biogeochemical cycling. While research in coastal science is fundamentally transdisciplinary—as drivers of biogeochemical and ecological processes often span scientific and environmental domains—traditional place–based approaches are still often employed to understand coastal ecosystems. We argue that a macrosystems science perspective, including the integration across distributed research sites, is crucial to understand how compounding disturbances affect coastal ecosystems. We suggest that many grand challenge questions, such as advancing continental-scale process understanding of extreme events and global change, will only be addressed in coastal ecosystems using a network-of-networks approach. We identify specific ways that existing research efforts can maximize benefit across multiple interested parties, and where additional infrastructure investments might increase return-on-investment along the coast, using the coastal continental United States as a case study.

While dominant species are known to be important in ecosystem functioning and community assembly, biodiversity responses to the presence of dominant species can be highly variable. Dominant species can increase the importance of deterministic community assembly by competitively excluding species in a consistent way across local communities, resulting in low site-to-site variation in community composition (beta-diversity) and nonrandom community structure. In contrast, dominant species could increase the importance of stochastic community assembly by reducing the total number of individuals in local communities (community size), resulting in high beta-diversity and more random community structure. We tested these hypotheses in a large, temperate oak-hickory forest plot containing a locally dominant tree species, pawpaw (Asimina triloba; Annonaceae), an understory tree species that occurs in dense, clonal patches in forests throughout the east-central United States. We determined how the presence of pawpaw influences local species diversity, community size, and beta-diversity by measuring the abundance of all vascular plant species in 1 × 1-m plots both inside and outside pawpaw patches. To test whether the presence of pawpaw influences local assembly processes, we compared observed patterns of beta-diversity inside and outside patches to a null model in which communities were assembled at random with respect to species identity. We found lower local species diversity, lower community size, and higher observed beta-diversity inside pawpaw patches than outside pawpaw patches. Moreover, standardized effect sizes of beta-diversity from the null model were lower inside pawpaw patches than outside pawpaw patches, indicating more random species composition inside pawpaw patches. Together these results suggest that pawpaw increases the importance of stochastic relative to deterministic community assembly at local scales, likely by decreasing overall numbers of individuals and increasing random local extinctions inside patches. Our findings provide insights into the ecological processes by which locally dominant tree species shape the assembly and diversity of understory plant communities at different spatial scales.

The dominant conceptual model for how river flow affects when and where riparian hardwood trees establish (the “recruitment box model”) considers streamflow recession and a survivable rate of stage decline to predict survival of seedling desiccation. However, to become established, plants must also survive the pre-seedling life stages and avoid inundation and scour mortality in high flows. We examine the relative importance of these flow-dependent mechanisms by representing them in a two-dimensional simulation model. Analysis of the model as applied to a low-gradient reach of a large mountain river indicates that the soil characteristic determining moisture elevation (the “capillary fringe” height) is the most important process driving establishment rates; also important are the dates of seed deposition, inundation mortality, and the time needed for sprouted seeds to develop roots. Root growth rate had only moderate effect on seedling survival. These results indicate that the conventional conceptual model of establishment is incomplete. At our site, natural rates of decline in soil moisture elevation exceeded root growth rates, so widespread establishment required periods of near-steady flows. Further, under both reservoir-controlled and unimpaired flow regimes, establishment was strongly determined by post-deposition flow increases: seeds deposited at elevations low enough to support rooting were often killed via inundation or scour in flow fluctuations that occurred under both reservoir-regulated and unregulated flow scenarios. When soil moisture dynamics are represented even simply, the survivable rate of stage decline is not constant but depends on capillary fringe height, seed elevation, and the duration of stage decline. A more complete conceptual model of hardwood establishment considers that seeds need to be deposited where soil is moist long enough to develop roots but far enough from the water's edge to avoid mortality in flow fluctuations; for soil moisture to remain within reach of roots, which could require unusually steady flows, a high capillary fringe, or favorable groundwater gradients; and to avoid mortality due to scour or inundation in winter high flows. Model sensitivity and lack of literature suggest the time and moisture requirements for seeds to develop roots and inundation mortality of seedlings as research priorities.

Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) control nitrification in terrestrial systems. Soil pH and substrate availability (NH₄⁺) can influence community composition, which may affect the contributions of these organisms to nitrification in forest soils. Using high-throughput sequencing, we identified the amoA of AOA and AOB from northern forest stands that occur across a natural gradient of nitrification, soil pH, and net N mineralization (i.e., NH₄⁺ availability). Specifically, we investigated changes in relative abundance and community composition of AOA and AOB across a soil pH and net N mineralization gradient, and how turnover in community composition is linked to nitrification. We found that soil pH was a stronger driver of AOA and AOB relative abundance than was NH₄⁺ availability. Generally, AOA and AOB turnover were positively associated with soil pH; however, some AOA taxa also displayed a negative association. Interestingly, the relative abundance of only a small number of AOA and AOB taxa was significantly associated with net nitrification rates. Our findings reveal that coexisting taxonomical groups of ammonia-oxidizers in forest soils have diverse responses to environmental factors, which influence how ammonia-oxidizer communities are structured, likely having direct implications for nitrification and the regulation of N cycling in forest systems.

In wet regions, temperature increases can prompt increases in vegetation growth. Vegetation responses are determined in part by N and P availability, yet the relative importance of N- versus P-cycling supporting growth is unclear. Prompted by studies demonstrating that warming-enhanced N cycling supports greater productivity and soil C stocks in warmer forests along a wet boreal forest transect, we tested the hypothesis that enhanced organic matter cycling supports greater P demand in relatively warm forests. We further asked whether evidence from soil and litterfall fluxes indicates increases in P demand are met in these forests or potentially pose a limit on warming-enhanced productivity. Elevated tree growth and litterfall rates coupled with similar litterfall P concentrations suggest P demand is greater at warmer sites. By assessing multiple soil N and P stocks, inputs, and stoichiometry, we observed three lines of evidence indicating that this greater P demand is met through a combination of plant tissue plasticity and adequate surface soil P supplies. First, warming-enhanced N-cycling results in an increase in N:P of surface soils and litterfall inputs indicating a reduction in needle litter P relative to N. Second, organic layer C:P and P stocks were maintained across latitude despite increases in litterfall P inputs in the warmest forests suggesting increased cycling and retention of P by trees. Third, in contrast with soil N, estimates of soil P residence times are not coupled with those of C, and soil C:P does not correlate with tree growth across sites signifying that N, not P, may limit tree growth in these forests. Results here provide evidence that increased productivity with warming and enhanced N cycling in wet boreal forests is not likely to be limited by available P over the decadal timescale represented by the temperature gradient along this climate transect. However, similarities observed between warming-enhanced N availability in the current study's forests and that in boreal forests receiving high N additions indicate a need to better understand how boreal trees may adapt to shifts away from N limitation. Such new knowledge is needed to improve our understanding of the longevity of this important climate feedback.