Camila Medeiros, University of California, Los Angeles, discusses her article: Simplification of woody plant trait networks among communities along a climatic aridity gradient
Motivation
Plants are enormously diverse across regions, even within specific ecosystems, and zooming in on individual plants, one finds great diversity among their traits. Variation of all kinds of traits can play a role in plant specialization to the environment, i.e., those that represent different plant organs (leaf, stem, roots), levels of organization (dimensions, structure, anatomy, nutrient composition), and functions (from photosynthesis to drought tolerance).
Inspired by the use of network analysis in recent decades to provide insights into system organization from genes to food webs to transportation infrastructure to social groups, plant ecologists have begun to use this approach to provide fresh answers to long-standing questions about whole plant adaptation, and how communities diverge in their phenotypes. In trait networks, traits are visualized as nodes and statistical trait-trait relationships as connections of a network.
Our study
The biodiverse California Floristic Province, CAFP, is an endlessly enlightening system to examine shifts in trait network architecture across a climatic gradient. The work is urgent because many of these ecosystems are under severe threat by humans (i.e., deforestation, land conversion) and natural disturbances (i.e., severe drought events, fire).
For each ecosystem across the CAFP, we created networks of the interrelationships among a wide range of traits measured for the most abundant species in each ecosystem. From these networks, we extracted indices of network complexity and connectivity and tested their relationship to climatic aridity, ecosystem productivity, and diversity. Finally, we focused on how traits themselves varied in their roles within these trait networks. We hypothesized that traits that are connected with more traits would be those that tend to vary less across species, as they would help maintain the “stability” of the networks.
Results and outlook
Consistent with our hypotheses, across communities from arid to moist, the network architecture varied from less to more interconnected and complex. Further, focusing on traits within the networks, traits with less variation across species were more interconnected.
We found a strong responsiveness of plant trait network architecture to climate across these communities that span a pronounced aridity gradient. This work provides evidence that a wide range of traits shift together when comparing communities. Communities in more arid environments showed a lower degree of phenotypic integration (i.e., connectivity and complexity), consistent with lesser niche differentiation. Our study highlights avenues to use trait networks to clarify plant environmental adaptation and trait associations that would influence species distributions, community assembly, and ecosystem resilience under changing climate.
