The northern Humboldt Current System (nHCS) is an area with high environmental variability that impacts key demographic and community-scale processes. Understanding the role and ecological implications of these interannual or long-term events is crucial in describing the dynamics of the nHCS community. Using catch data from pelagic assessment surveys from 1983 to 2019 and the community trajectory analysis framework, we tested and characterised the patterns and compositional dynamics of the nHCS pelagic fish community over space and time. Spatially, changes were evaluated for ecological regions with similar community composition identified through hierarchical clustering with spatial constraint. We found that the community is in constant inter-annual variability consistent with the long-term warm and cold periods of the system. A long trajectory segment suggests a community regime shift between 1994 and 1999, years associated with a change in the average oceanographic conditions in the system and an extreme El Niño event (1997-98). After 1999, we identified a period where the community was constantly changing and dominated by coastal species. These long-term community changes were not homogeneous over the ecological areas, finding a lower temporal variability in the coastal area than in the northern and offshore. The main factor controlling the spatial and temporal dynamics of the nHCS pelagic fish community seems to be the long and short-term environmental conditions in the system. This study helps to understand the magnitude and direction of pelagic fish community changes and define the community’s recovery process after an event-driven change.

Vapor Pressure Deficit (VPD, atmospheric drought) and soil water potential (Ψsoil, soil drought) have both been reported to affect terrestrial plant water stress, plant functions (growth, stomatal conductance, transpiration) and vulnerability to ecosystem disturbances (mortality or vulnerability to wildfires). Which of atmospheric drought or soil drought has the greatest influence on these responses is yet an unresolved question. Using a state-of-the-art soil-plant-atmosphere hydraulic model, we conducted an in-silico experiment where VPD and Ψsoil were manipulated one at a time to quantify the relative importance of atmospheric vs soil drought on most critical plant functions. The model simulates the combined effects of soil drought and atmospheric drought on plant water potential (ΨPlant), a physiologically meaningful metric of plant water status driving plant turgor, stomatal conductance, hydraulic conductance or water content, and thus mortality and fire risks. Contrary to expectations, we showed that VPD had a weaker effect than Ψsoil on tree water stress and forest disturbances risk (i.e leaf moisture content). While physiological responses associated with low water stress such as stomatal closure or turgor loss could be driven by both VPD or soil drought, consequences of extreme water stress such as hydraulic failure, leaf desiccation and vulnerability to wildfires were almost exclusively driven by low Ψsoil. Our results therefore suggest that most plant functions are affected by VPD through its cumulative effect on Ψsoil via increased plant transpiration, rather than through a direct instantaneous effect on plant water potential. We argue that plant hydraulics provide a strong foundation for predicting tree and terrestrial ecosystem responses to climate changes and propose a list of explanations and testable hypotheses to reconcile plant hydraulic theory and observations of soil and atmospheric drought effects on plant functions.

Growing evidence that individuals of many generalist animals behave as resource specialists has attracted research interest for its ecological and evolutionary implications. Although variation in resource preferences is critical for developing a general theory of individual specialization, it remains to be shown whether diverging preferences can arise among individuals sharing a similar environment and whether these are stable enough to be ecologically relevant. We addressed these issues by means of common garden experiments in feral pigeons (Columba livia), a species known to exhibit resource specialization in the wild. Food-choice experiments on wild-caught pigeons and their captive-bred descendants showed that variation in food preferences can easily arise within a population and that this variation may represent a substantial fraction of the population niche. However, a cross-fostering experiment revealed that the genetic and early common-environment components of food preferences were low, reducing their stability and eroding niche variation in the long-term.