Warming and shifts in litter quality drive multiple responses in freshwater detritivore communities.

Aquatic detritivores are highly sensitive to changes in temperature and leaf litter quality caused by increases in atmospheric CO2. While impacts on detritivores are evident at the organismal and population level, the mechanisms shaping ecological communities remain unclear. Here, we conducted field and laboratory experiments to examine the interactive effects of changes in leaf litter quality, due to increasing atmospheric CO2, and warming, on detritivore survival (at both organismal and community levels) and detritus consumption rates. Detritivore community consisted of the collector-gathering Polypedilum (Chironomidae), the scraper and facultative filtering-collector Atalophlebiinae (Leptophlebiidae), and Calamoceratidae (Trichoptera), a typical shredder. Our findings reveal intricate responses across taxonomic levels. At the organismal level, poor-quality leaf litter decreased survivorship of Polypedilum and Atalophlebiinae. We observed taxon-specific responses to warming, with varying effects on growth and consumption rates. Notably, species interactions (competition, facilitation) might have mediated detritivore responses to climate stressors, influencing community dynamics. While poor-quality leaf litter and warming independently affected detritivore larvae abundance of Atalophebiinae and Calamoceratidae, their combined effects altered detritus consumption and emergence of adults of Atalophlebiinae. Furthermore, warming influenced species abundances differently, likely exacerbating intraspecific competition in some taxa while accelerating development in others. Our study underscores the importance of considering complex ecological interactions in predicting the impact of climate change on freshwater ecosystem functioning. Understanding these emergent properties contributes to a better understanding of how detritivore communities may respond to future environmental conditions, providing valuable insights for ecosystem management and conservation efforts.

Precipitation and predation risk alter the diversity and behavior of pollinators and reduce plant fitness.

Biotic and abiotic factors may individually or interactively disrupt plant-pollinator interactions, influencing plant fitness. Although variations in temperature and precipitation are expected to modify the overall impact of predators on plant-pollinator interactions, few empirical studies have assessed if these weather conditions influence anti-predator behaviors and how this context-dependent response may cascade down to plant fitness. To answer this question, we manipulated predation risk (using artificial spiders) in different years to investigate how natural variation in temperature and precipitation may affect diversity (richness and composition) and behavioral (visitation) responses of flower-visiting insects to predation risk, and how these effects influence plant fitness. Our findings indicate that predation risk and an increase in precipitation independently reduced plant fitness (i.e., seed set) by decreasing flower visitation. Predation risk reduced pollinator visitation and richness, and altered species composition of pollinators. Additionally, an increase in precipitation was associated with lower flower visitation and pollinator richness but did not alter pollinator species composition. However, maximum daily temperature did not affect any component of the pollinator assemblage or plant fitness. Our results indicate that biotic and abiotic drivers have different impacts on pollinator behavior and diversity with consequences for plant fitness components. Even small variation in precipitation conditions promotes complex and substantial cascading effects on plants by affecting both pollinator communities and the outcome of plant-pollinator interactions. Tropical communities are expected to be highly susceptible to climatic changes, and these changes may have drastic consequences for biotic interactions in the tropics.

The role of spider hunting mode on the strength of spider-plant mutualisms.

The strength and outcome of mutualistic interactions can be highly dependent on the combination of traits of the species involved. Distinct foraging strategies (e.g., hunting mode) of mutualistic predators may cause predator-prey interactions to vary, potentially affecting the strength of trophic cascades. We evaluate the causes of variation in the strength of spider-plant mutualisms by focusing on contrasting hunting modes of two spiders: an actively hunting lynx spider (Peucetia sp.) and a sit-and-wait crab spider (Misumenops argenteus). We manipulated spider species composition by assigning each plant to one of the following treatments: (1) no spiders; (2) sit-and-wait spiders only; (3) actively hunting spiders only; (4) actively hunting + sit-and-wait spiders. We then examined the independent and interactive effects of spider species on floral herbivory and fitness of the glandular trichome-bearing plant, Trichogoniopsis adenantha (Asteraceae). Both spider species increased plant fitness by suppressing herbivores and increasing ovary fertilization, but the overall net benefit of spiders was contingent on spider hunting mode. Sit-and-wait spiders promoted stronger positive cascading effects compared to actively hunting spiders. The combination of spider species suppressed herbivores in an additive manner; their combined impact on plant fitness, however, was lower than expected, suggesting that the inter-specific interaction between spiders is slightly antagonistic. Thus, both spider species combined weakened the strength of this spider-plant mutualism. Our findings offer a general framework for understanding the critical role of predator foraging mode in trophic cascades.