No abstract

No abstract

Premise of research. Small populations on small islands are intrinsically more vulnerable to population decline and extinction. Nevertheless, small native populations that occur on multiple islands may have life-history characteristics that buffer impacts from novel disturbance regimes, and, rather than contracting, populations may be expanding. We monitored three populations of the orchid Brassavola cucullata from two Caribbean islands and asked what the likelihood of population persistence is.Methodology. Over 3-4 yr, we recorded growth, fruit production, herbivory, recruitment, and mortality for all plants in each of our populations. We assessed persistence and predicted possible population changes using both population projection models (PPMs) and integral projection models (IPMs). Our results include a mixture of traditional indexes (l and elasticities) and more recent indexes (transient dynamics and nonlinear sensitivities).Pivotal results. Growth, reproduction, and predicted population persistence varied among years and islands. IPMs and PPMs gave similar results. The overall trend is toward a reduction in population growth rates, although population reactivity may buffer this pattern in the short term (l > 1). Populations would be extremely vulnerable to reduction if small plants dominated, yet even with an abundance of large plants, substantial reductions in population density are possible. Medium and larger plants contribute more to the persistence of the population, yet the survival and growth of small individuals might have greater effects on l if retrogression is observed. To attain population stability, effective recruitment rates must increase dramatically.Conclusions. Populations of perennial plants on small islands can fluctuate substantially, suggesting a degree of vulnerability. While B. cucullata shows a general trajectory of decline, there are some signs of stability despite deforestation and herbivore activity. The outlook is precarious for the Saba population given the predominance of younger plants, and all three populations could decline if spasmodic recruitment fails to occur, which may happen if disturbance regimes change and the ongoing warming and drying trends persist.

The introduced tree species Spathodea campanulata (Bignoniaceae) forms novel forests in Puerto Rico, these having emerged after the abandonment of fields in the mid‐20th century and resulting in forests with a new species composition. We assessed bryophyte species richness in these novel forests and sought correlations with geological substrate, past land use, forest edge and patch area, forest structure, elevation, microhabitat diversity, tree species richness, and microclimatic conditions. Transects were established (edge and forest interior) in nine moist forest patches dominated by Spathodea in north‐central Puerto Rico. These Spathodea forest patches ranged from 0.6 to 9 ha. ANOVA, Chi‐square, correlation, and cluster analyses were used in data analyses. We found 57 bryophyte species. There was a significant difference in bryophyte richness among patches. Those on karst exhibited highest bryophyte richness due to microhabitat diversity, past land use, and shorter hydroperiods. Alluvial sites scored lowest in bryophyte species richness, and forest structure was important for bryophyte communities on these sites. Significant differences in temperature, relative humidity, and light intensity were observed between edge and forest interior. These appeared important for establishing bryophyte species cover but not richness and composition. Microhabitat diversity, patch area, and forest age were more related to bryophyte species richness than elevation, exposed edge, and tree species richness, regardless of geologic substrate. Collectively, Spathodea patches were similar to mature forests on the Island with respect to bryophyte species richness and composition. Novel Spathodea forests have conservation value due to their habitat suitability for bryophyte communities.