Environmental management typically seeks to increase or maintain the population sizes of desirable species and to decrease population sizes of undesirable pests, pathogens, or invaders. With changes in population size come long-recognized changes in ecological processes that act in a density-dependent fashion. While the ecological effects of density dependence have been well studied, the evolutionary effects of changes in population size, via changes in ecological interactions with community members, are underappreciated. Here, we provide examples of changing selective pressures on, or evolution in, species as a result of changes in either density of conspecifics or changes in the frequency of heterospecific versus conspecific interactions. We also discuss the management implications of such evolutionary responses in species that have experienced rapid increases or decreases in density caused by human actions.

Domestication of crops has changed how crops shape their associated microbial communities compared with their progenitors. However, studies testing how crop domestication-driven differences in rhizosphere microbial communities affect plant health are limited mostly to specific symbiont pairings. By conducting a soil manipulation greenhouse study, we examined plant growth and yield in response to differences in microbial communities and nutrient availability across a variety of wild, landrace, and commercially available 'Modern' potatoes. Coupled with this, we conducted 16S and internal transcribed spacer (ITS) amplicon sequencing to examine plant host- and soil treatment-driven differences in microbial community composition on potato plant roots. We found that the plant response to microbes (PRM) was context dependent. In low nutrient conditions, landraces responded positively to the presence of live soil microbial inocula. Conversely, modern potato varieties responded positively only in high nutrient conditions. Amplicon sequencing found differences in bacterial communities due to environmental and temporal factors. However, potato clade (e.g. Andigenum, Chiletanum, Solanum berthaultii, and 'Modern') alone did not lead to differences in microbial communities that accounted for PRM differences. Differences in PRM between landraces and modern potatoes, and the correlation of PRM to microbial diversity, suggest that domestication and subsequent breeding have altered the S. tuberosum response to rhizosphere microbiomes between Andigenum, Chiletanum, and North American potato varieties.