Ecology最新文献

A fundamental question in ecology is why plant communities have large trait space yet strong coordination among those traits across large scales, despite these patterns seeming contradictory. Answering this question requires quantitatively linking the geographic distribution of trait space and coordination with gross primary productivity (GPP). We leveraged an unprecedented large-scale dataset of nine leaf traits for 5718 species-site combinations with simultaneous field measurements of plant community composition in 64 naturally assembled communities to investigate trait spaces (hypervolume, quantity dimension) and trait compactness (coordination, efficiency dimension) and their influence on GPP. Trait space and compactness combined explained 72% of the variation of GPP. Interestingly, a larger trait space (more diverse trait combinations) drove higher GPP in resource-poor communities, while higher trait compactness (greater coordination of traits) determined higher GPP in resource-rich communities. Our findings provide a new perspective that natural plant communities increase both trait space and compactness to improve GPP, shedding light on the development of multidimensional functional ecology.

The enemy release hypothesis posits that introduced species escape some of their predators, pathogens, and parasites when they move to a new range. We used a systematic review to compile data from 691 contrasts of enemy release spanning plants, animals, and algae in aquatic and terrestrial systems worldwide. Data from 311 biogeographic contrasts (between home and new range) revealed that on average, a species experiences only 43% as much enemy pressure in their introduced range as they experience in their native range. Data from 380 community contrasts (between native and introduced species) revealed that introduced species experience on average 70% of the enemy pressure that their native congeners endure. Interestingly, one third (36%) of contrasts showed higher, rather than lower, enemy pressure on the introduced population. Enemy release was well supported in contrasts of the diversity of enemies and enemy damage but not significant in contrasts of host fitness, suggesting that while introduced populations are attacked by fewer enemies, this does not always result in higher fitness. We also found that biogeographic enemy release was higher in mollusks and fish but lower in insects and algae, indicating that certain taxa may be favored by enemy release. We hope that an improved understanding of the extent to which introduced species are released from enemy pressures will help managers to identify good opportunities for biocontrol and to understand the factors likely to be affecting the success of invasive species.

Thermophilization of communities, or shifts in composition favoring more warm-adapted species, over time and space is a common response to warming from global climate change and localized effects of land-use change. However, the interplay between community thermophilization driven by temporal warming in global climate and spatial warming in local climate is not well explored empirically. Here, we use long-term ecological monitoring of ground-dwelling arthropod communities over twenty years, sited in desert and urbanized habitats, to address the joint effects of spatiotemporal warming on community thermophilization. We found spatial convergence of high community thermophily among warm desert and highly urbanized sites, implicating temperature as a major driver of community composition. However, we found unexpected temporal declines in community thermophily, the magnitude of which depended upon space. Declines were found in urbanized sites, but not desert sites. There was evidence of both increases in occurrence of heat-intolerant taxa and decreases in heat-tolerant taxa from urban sites. Our study demonstrates the contingency of responses to recent climate change based on contemporary land-use change.

Trait-based approaches can improve ecological understanding by linking fitness to the environment. The trilateral life history model is an expansion of r- and K-selection theory that reflects trade-offs between juvenile survival, fecundity, and generation time and describes differential survival of species across environmental gradients. We used this framework to generate and test hypotheses regarding community assembly and the validity of such a model in two disparate taxonomic groups, freshwater mussels and fish. We assessed the distribution of mussel and fish life history strategies across 80 sites spanning aspects of the river continuum concept within the Ouachita Highlands (USA) and asked if their distributions are predicted by a similar life history strategy framework. Because mussel and fish assemblages should both be structured by selective forces in an up- to downstream trajectory, we expected both taxa to converge on more species-rich assemblages with a greater proportion of equilibrium strategists in larger, more stable downstream habitats. We found that both mussel and fish species richness increased with watershed area as well as the proportion of equilibrium strategists in the assemblages. Our study validates the use of the trilateral life history model to test hypotheses about the distribution patterns of two coevolved taxonomic groups.

Algal dynamics are fundamental drivers of lotic ecosystem processes. Although rivers tend to be heterotrophic and have low standing stocks of autotrophic biomass, filamentous algae can cause nuisance algal blooms that alter the structure of the autotrophic assemblage. Still, the influence of these blooms on ecosystem processes can be variable. Here, we examined the structural and functional contribution of filamentous and epilithic algae by linking algal biomass measurements to daily primary production fluxes throughout two growing seasons in six sites along the Upper Clark Fork River, an open canopy, snow melt river in western Montana, USA. We partitioned daily productivity estimates across different algal groups using the spatial and temporal variability in algal assemblages across our six sites. By using reach-scale metabolism estimates, we assessed the in situ functional rates of individual algal groups. Throughout two growing seasons, we measured high fluxes of ecosystem productivity and spatially variable filamentous algal blooms. We found that the filamentous algal blooms determined the ecosystem structure in terms of total biomass and algal turnover times, but not the ecosystem functions of gross primary productivity, ecosystem respiration, or net production. Whole-reach estimates of epilithic and filamentous algae growth rates were 0.30 and 0.026 day$��{\hspace{0.17em}}^{�-�1�}�$ respectively, which are similar to rates measured in mesocosms. The epilithic algae grew and turned over rapidly, dominating total biomass production and driving ecosystem function while filamentous algae grew slowly and built up large amounts of biomass during a growing season, shaping the structure, but not function, of the ecosystem.

How do individuals tolerate both hot and cold climates of our planet? One possibility is that organisms have plastic traits, such as thermal tolerance, that allow them to function in highly variable environments. In this study, we tested whether phenotypic plasticity of temperature tolerance (i.e., acclimatization in the field and acclimation in the lab) occurs in the red harvester ant, Pogonomyrmex barbatus, at two temporal scales. We first measured the upper and lower critical thermal limits (CT_max and CT_min) of ants monthly for 2 years while concurrently measuring environmental conditions. Both CT_max and CT_min covaried with temperature in a predictable way; values increased in a positive, linear manner. We then experimentally tested whether CT_max and CT_min could shift within a shorter time period by exposing subcolonies of ants to cool (10°C), moderate (20°C), and hot (30°C) temperatures for 10 days. CT_max increased only slightly at the hottest temperature treatment (+1.2°C); however, CT_min increased considerably under both moderate (+2.6°C) and hot treatments (+3.8°C). Combined, our results suggest that the thermal tolerance of ants may be more plastic than originally hypothesized, potentially aiding an already thermophilic clade in future climate scenarios.

Costs of reproduction are predicted to shift under climate change, but the extent to which weaker or stronger costs influence population responses to interannual climate variation is unknown. We asked how seasonal climate, manipulated rainfall, and costs of reproduction influence vital rates and population growth in a long-lived herbaceous perennial plant, Primula hendersonii, across an ongoing rainfall manipulation experiment in oak savanna of northwestern North America. Simulated drought reduced population growth rates, and vital rates (e.g., probability of flowering, individual growth) responded individualistically to variation in winter, spring, and summer temperatures, although not to variation in seasonal precipitation. However, only warmer spring temperatures were associated with a decline in population growth rates. Although we observed a weak negative effect of past reproduction on growth and future reproduction for large individuals, these costs of reproduction ultimately did not influence population growth. Further, observational and manipulative experiments to detect costs of reproduction suggest subtle differences in cost expression. We show that direct climate drivers had a stronger effect on population growth than indirect changes in costs of reproduction and may be more important for understanding population persistence under climate change.

Climate change impacts ecosystems directly through differences in species-specific responses as well as indirectly through changes to the strength of species interactions. To predict how species will be impacted by ongoing environmental change, we need to better understand the relative roles of these direct and indirect effects. Salinity is a strong driver of ecological patterns and processes, and salinity regimes in coastal regions are expected to be altered by climate change through the intensification of the hydrological cycle and via climate-driven shifts in the timing and strength of the spring freshet. We hypothesized that hyposalinity can indirectly affect the intertidal community by excluding a dominant guild of herbivores, limpets in the genus Lottia. To test this hypothesis, we (1) conducted intertidal diversity surveys in regions of high versus seasonally low salinity in the Strait of Georgia, British Columbia, (2) conducted laboratory salinity tolerance trials for two important grazers (Lottia pelta and Lottia digitalis) and one primary producer (Ulva sp.), and (3) experimentally manipulated the abundance of grazers in these two regions. We show that rocky intertidal shores from two regions of disparate salinity regimes are distinct in their intertidal communities: low salinity sites were composed primarily of Mytilus trossulus, Fucus distichus, and Ulva sp., whereas high salinity sites were dominated by Chthamalus dalli, Lottia spp., and Mastocarpus sp. Our laboratory trials confirmed that freshwater inputs experienced in the low salinity region resulted in hyposaline levels which exceeded the tolerance of Lottia spp., but not that of Ulva sp. Further, we show that by excluding grazers in high salinity sites, these communities more closely resemble those of the low salinity sites than those of other high salinity sites with grazers present. Together, these results demonstrate that the pattern of distinct estuarine intertidal communities in low versus high salinity regions in the Strait of Georgia may be largely driven by the indirect effects of freshwater inputs, mediated by salinity-driven differences in herbivore population size and thus grazing pressure.