Evolutionary origins for ecological patterns in space

Abstract

Historically, many biologists assumed that evolution and ecology acted independently because evolution occurred over distances too great to influence most ecological patterns. Today, evidence indicates that evolution can operate over a range of spatial scales, including fine spatial scales. Thus, evolutionary divergence across space might frequently interact with the mechanisms that also determine spatial ecological patterns. Here, we synthesize insights from 500 eco-evolutionary studies and develop a predictive framework that seeks to understand whether and when evolution amplifies, dampens, or creates ecological patterns. We demonstrate that local adaptation can alter everything from spatial variation in population abundances to ecosystem properties. We uncover 14 mechanisms that can mediate the outcome of evolution on spatial ecological patterns. Sometimes, evolution amplifies environmental variation, especially when selection enhances resource uptake or patch selection. The local evolution of foundation or keystone species can create ecological patterns where none existed originally. However, most often, we find that evolution dampens existing environmental gradients, because local adaptation evens out fitness across environments and thus counteracts the variation in associated ecological patterns. Consequently, evolution generally smooths out the underlying heterogeneity in nature, making the world appear less ragged than it would be in the absence of evolution. We end by highlighting the future research needed to inform a fully integrated and predictive biology that accounts for eco-evolutionary interactions in both space and time.

Keywords: eco-evolutionary dynamics; local adaptation; spatial ecology.

Fig. 1.

Widespread evidence for microgeographic adaptation. Many species adapt at surprisingly fine scales as indicated by red lines, including (clockwise from bottom left) banding in land snails, camouflaged isopods, allele frequencies in mice, feeding morphology in fish, feeding behavior in salamanders, herbivore-defended trees, and toxin-tolerant grass.

Fig. 2.

Evolution can dampen, amplify, and create spatial ecological patterns, affecting everything from population abundances to species ranges. (Left) Evolution can dampen an existing ecological spatial pattern across an environmental gradient by reducing the slope. (Middle) Alternatively, evolution might amplify the original ecological spatial pattern. (Right) Evolution can also create a pattern where none existed before by creating a nonzero slope (changing unpatterned into patterned half) or completely novel patterns (e.g., new species composition indicated in purple patches). Numbered mechanisms correspond to those found in Table 1.

Fig. 3.

Results from literature review including overall patterns, by ecological level, by mechanism, and by geographic origin and taxonomic group. Evolution usually dampens existing ecological patterns (blue), especially at population, metapopulation, and range levels. Evolution also can amplify existing patterns (yellow), especially for positive species interactions and resource-related ecosystem properties. Sometimes evolution creates new patterns (orange) when genetic variation within foundation or keystone species creates differences in dependent communities. Fourteen mechanisms grouped into five categories (details in Table 1) explain these divergent outcomes. We depict the dominant continental origins and taxonomic groups (most common species named) with icon size proportional to number of studies. Summed percentages exceed 100% because some studies include multiple effects. In waffle graphs, each block equals five studies or 1% of studies.