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Environmental variation along an elevational gradient can yield phenotypic differentiation resulting from varying selection pressures on plant traits related to seasonal responses. Thus, genetic clines can evolve in a suite of traits, including the circadian clock, that drives daily cycling in varied traits and that shares its genetic background with adaptation to seasonality. We used populations of annual Mimulus laciniatus from different elevations in the Sierra Nevada in California to explore among-population differentiation in the circadian clock, flowering responses to photoperiod, and phenological traits (days to cotyledon emergence, days to flowering, and days to seed ripening) in controlled common-garden conditions. Further, we examined correlations of these traits with environmental variables related to temperature and precipitation. We observed that the circadian period in leaf movement was differentiated among populations sampled within about 100 km, with population means varying by 1.6 h. Significant local genetic variation occurred within 2 populations in which circadian period among families varied by up to 1.8 h. Replicated treatments with variable ecologically relevant photoperiods revealed marked population differentiation in critical day length for flowering that ranged from 11.0 to 14.1 h, corresponding to the time period between late February and mid-May in the wild. Flowering time varied among populations in a 14-h photoperiod. Regardless of this substantial population-level diversity, obvious linear clinality in trait variability across elevations could not be determined based on our genotypic sample; it is possible that more complex spatial patterns of variation arise in complex terrains such as those in the Sierra Nevada. Moreover, we did not find statistically significant bivariate correlations between population means of different traits. Our research contributes to the understanding of genetic variation in the circadian clock and in seasonal responses in natural populations, highlighting the need for more comprehensive investigations on the association between the clock and other adaptive traits in plants. [ABSTRACT FROM AUTHOR]

Foundation species and invasive species strongly influence community diversity and structure, but typically in different ways. However, when widespread invasive species provide novel habitat within a community, their net effect may depend on both the environment and community composition. Fouling communities in northern and southern California harbors were surveyed to determine whether there was variation between two locations in the percent cover of an invasive bryozoan, Watersipora subtorquata (d'Orbigny, 1852), and its relationship to community diversity and composition in these two environments. Diversity significantly differed between locations and had a location-dependent association with W. subtorquata abundance. Communities were significantly dissimilar between locations, and W. subtorquata abundance had the highest percent contribution to community dissimilarity when compared to other species in the community. These results suggest that invasive species may have both facilitative and inhibitive relationships with species in a community, but that the net balance of these interactions depends on both the environmental and community context. [ABSTRACT FROM AUTHOR]

Clines of biological variation result from variation in physical environmental conditions. We report new reproductive data for a population of antelope ground squirrels, Ammospermophilus leucurus, at the northern geographic limit of this species. We then analyze reproductive patterns at 3 sites spanning the entire north-south extent of the geographic range, covering more than 2,500 km and 21 degrees of latitude. The overall breeding season of populations is relatively short in Oregon (42°N) and California (37°N), but in Baja California (24°N) it encompasses half a year. Mean litter size decreases significantly from north to south, from 9.3 (SD = 1.8) per litter in Oregon to 5.9 (SD = 1.5) in Baja California. Major shifts in seasonality of precipitation and ecosystem composition and diversity are associated with longer breeding season and lower litter size at the southern geographic extreme of A. leucurus. The environmental predictability for the northern populations is due to "constancy," whereas the predictability at the southern extreme is due to "contingency." The observed latitudinal reproductive patterns represent local responses of populations to environmental conditions and the related characteristics of North America's major desert ecosystems. [ABSTRACT FROM AUTHOR]

Both foundation species and introduced species have exceptional influence on community diversity and structure, though they have historically been thought to have opposite effects. However, when introduced species can provide novel habitat within a community, their benefit to the community as a foundation species may outweigh their cost as an invader. The magnitude or direction of species interactions can depend on the environment, thus the net effect of introduced foundation species can vary across different environmental factors. A settlement tile experiment was conducted on the fouling communities of California harbors to determine whether the effects of a widespread invasive bryozoan, Watersipora subtorquata , vary between two locations in its California range, Alamitos Bay and Bodega Harbor. Treatments with live and dead colonies and two sizes of blank tiles were used to evaluate the effects of colony structure and available bare substrate on both mobile and sessile species in the community. Though mobile invertebrate communities in each location across treatments were not significantly dissimilar to each other, communities on large tiles were significantly dissimilar to other communities in each location. Mobile species richness was greatest on live colony and small tiles in Bodega, but greatest on dead colony and large tiles in Alamitos. Both the diversity and community structure of sessile invertebrates across treatments differed significantly between regions. Diversity was greatest on dead colony tiles in Alamitos, where communities were more dissimilar across treatments, but was greatest on live W. subtorquata tiles in Bodega where communities were less dissimilar across treatments. These results highlight the potential for W. subtorquata to have location-dependent net effects on the community throughout its invasive range as a foundation species. • No significant effect of W. subtorquata on benthic community diversity or richness. • Location-dependent effects on benthic community dissimilarity by W. subtorquata. • W. subtorquata competes with colonial tunicates for space; inhibits lateral growth. • Novel example of facilitation; sponge epizoic on W. subtorquata colonies. [ABSTRACT FROM AUTHOR]