Small effective size limits performance in a novel environment

Abstract

Understanding what limits or facilitates species' responses to human‐induced habitat change can provide insight for the control of invasive species and the conservation of small populations, as well as an arena for studying adaptation to realistic novel environments. Small effective size of ancestral populations could limit the establishment in, or response to, a novel or altered habitat because of low genetic variation for ecologically important traits, and/or because small populations harbor fixed deleterious mutations. I estimated the fitness of individuals from populations of the endangered plant Hypericum cumulicola, of known census and effective size, transplanted into native scrub habitat and unpaved roadsides, which are a novel habitat for this species. I found a significant positive relationship between estimates of population size and mean fitness, but only in the novel roadside habitat. Fitness was more than 200% greater in the roadside habitat than the scrub, mostly due to increased fecundity. These results combined with previous estimates of heterosis in this species suggest that fixed deleterious mutations could contribute to lower fitness of field transplants from small populations in the novel environment.

A demographic ménage à trois: interactions between disturbances both amplify and dampen population dynamics of an endemic plant

“…Shorter‐lived scrub endemics of the same region, such as Hypericum cumulicola and Paronychia chartacea (Quintana‐Ascencio, Weekley & Menges ; Schafer et al . ; Oakley ), experienced higher fecundity but more variable survival in roadsides. Higher survival rates in L. ohlingerae and increasing fecundity in roadsides may result from decreased competition in this human‐disturbed habitat (Petrů & Menges ).…”

“…Anthropogenic disturbance along sandy roads can increase fecundity, likely due to reduced below‐ground competition, and population instability (Quintana‐Ascencio, Weekley & Menges ; Schafer et al . ; Oakley ). Anthropogenic disturbances can also interact with other drivers, such as herbivory and fire, in affecting populations.…”

Does source population size affect performance in new environments?

“…By examining the performance of multiple populations in natural common gardens and reciprocal transplants, however, we were able to further clarify some aspects of the relationship between population size and performance. Common garden experiments allowed us to control for confounding effects if fitness is only examined observationally in each population's native environment (Oakley ) or through home‐away comparisons. Similar to our home versus away analysis, we found that large populations tended to exhibit improved performance in their native environments relative to novel environments.…”

“…Small populations either (i) outperformed large populations (Hooftman et al. ), (ii) exhibited no loss of fitness or were outperformed by larger populations only in more benign environmental conditions (Oakley ), or (iii) exhibited reduced performance in increasingly dissimilar environments relative to their native environment (Bowman et al. ).…”

Conservation genetics and breeding system of Penstemon debilis (Plantaginaceae), a rare beardtongue endemic to oil shale talus in western Colorado, USA

“…As gene flow between populations decreases, genetic drift may also cause populations to become differentiated from one another (Ledig et al, ; Gemmill et al, ; Young & Clarke, ). Small populations are also vulnerable to environmental stochasticity, catastrophe, and loss of habitat to human activities (Ouborg et al, ; Oakley, ), resulting in reduced capacity for adaptation to changing conditions (Willi et al, ). Rare, endemic plant species with edaphic specializations are especially vulnerable to extinction or extirpation due to loss of habitat and subsequent population size reduction (Frankham, ; Leimu et al, ; Reed, ; Gordon et al, ).…”