John G. Lambrinos

HOW INTERACTIONS BETWEEN ECOLOGY AND EVOLUTION INFLUENCE CONTEMPORARY INVASION DYNAMICS

The literature on biological invasions has principally focused on understand- ing the ecological controls and consequences of invasions. Invading populations, however, often experience rapid evolutionary changes associated with or soon after their introduction. Ecological and evolutionary processes can, therefore, potentially interact over relatively short timescales. A number of recent studies have begun to document these interactions and their effect on short-term invasion dynamics: (1) The degree to which founder effects, drift, and in- breeding alter the genetic composition of introduced populations is mediated by migration and dispersal patterns, the population dynamics of founding populations, and life history. The genetic changes associated with founding can themselves feed back on population dynamics and life history. (2) Patterns of human-mediated dispersal and landscape change can influence the frequency and pattern of hybridization, which in turn can alter invasion dynamics. These altered invasion dynamics can influence the frequency and pattern of subsequent hybridization and introgression. (3) Strong selection can rapidly generate eco- typic specialization. Dispersal patterns, founder effects, genetic system, and life history influence the rate of local adaptation, its persistence, and its distribution in a landscape. (4) Introduced populations are subject to selection on life history traits and can serve as selective pressure on the life history traits of native populations. Life history evolution in both natives and aliens can influence ecological interactions and population dynamics, which in turn can influence the evolution of life history. Too few studies have investigated these interactions to definitively assess their overall generality or to determine how the relative interaction strength of ecology and evolution varies across taxa or ecosystems. However, the studies that do exist report interactions from a wide breadth of taxa and from all stages in the invasion process. This suggests that ecological-evolutionary interactions may have a more pervasive influence on contemporary invasion dynamics than previously appreciated, and that at least in some situations an explicit understanding of the contemporary co-influence of ecology and evolution can produce more effective and predictive control strategies.

THE VARIABLE INVASIVE SUCCESS OF CORTADERIA SPECIES IN A COMPLEX LANDSCAPE

It is likely that plant invasions result from complex interactions between species traits, community traits, and abiotic conditions. Despite this, there have been few experimental studies that directly examine these interactions. Two morphologically similar perennial grass species in the genus Cortaderia are currently invasive pests in California, but their patterns of invasion differ. In this study I experimentally compared the performance of the two species across four vegetation types in central California. I examined how the different invasive patterns of the species result from differential responses to environmental factors that vary over relatively small spatial and temporal scales. Cortaderia selloana had consistently higher seed germination than C. jubata, but germination rates interacted significantly with soil disturbance and habitat type, and these interactions varied between experimental years. When mammalian herbivores were excluded, the principal cause of transplant mortality was physiological stress, and C. selloana transplants had greater survivorship than C. jubata transplants in all habitats except maritime chaparral. In the presence of mammalian herbivores, however, herbivory became the dominant source of transplant mortality, and the survivorship of both species was indistinguishable in all habitats. At the seasonal wetland site, patterns of transplant survivorship varied significantly between years, probably as a result of increased competition for water during the second experimental year. Transplants of the two species did not differ significantly in growth except at the seasonal wetland site where C. selloana transplants added significantly more leaf area than C. jubata transplants. These results indicate that the relative invasive potential of C. selloana and C. jubata is strongly moderated by the presence of generalist herbivores. The influence of herbivory is in turn dependent on the community type. In addition, plant competitors can modify the invasive success of the two species, but the effect of competitors varies with seasonal differences in resource supply. Although important mechanisms that influence the invasion process can be identified, the complex invasion dynamics exhibited by these morphologically similar species across relatively small spatial and temporal scales suggest that overly broad invasion rules will be of little practical utility in the regional management of invasive species.

Physical Ecosystem Engineers and the Functioning of Estuaries and Coasts

A great diversity of organisms modify the physical structure of estuarine and coastal environments. These physical ecosystem engineers – particularly, dune and marsh plants, mangroves, seagrasses, kelps, reef-forming corals and bivalves, burrowing crustaceans, and infauna – often have substantive functional impacts over large areas and across distinct geographic regions. Here, we use a general framework for physical ecosystem engineering to illustrate how these organisms can exert control on sedimentary processes, coastal protection, and habitat availability to other organisms. We then discuss the management implications of coastal and estuarine engineering, concluding with a brief prospectus on research and management challenges.

The Importance of Nurse Associations for Three Tropical Alpine Life Forms

Abstract We investigated biotic and abiotic associations for four growth forms in Chiles Parque Nacional Lauca, a tropical alpine puna ecosystem. We determined the biotic associations between Parastrephia lucida (Meyen) Cabr. [Asteraceae] and Festuca orthophylla Pilger. [Poaceae]. To determine if F. orthophylla was acting as a nurse plant for P. lucida, we used chi-square analysis to test for nurse plant effects. Our results indicated that F. orthophylla roots more often on bare ground and that P. lucida grows more often in association with F. orthophylla than would be expected. In testing for abiotic associations, we observed that both a tree, Polylepis tarapacana [Rosaceae], and a cactus, Tephrocactus ignescens [Cactaceae], showed positive abiotic associations with large boulders. These studies indicate that in an extreme environment, such as the South American puna, abiotic and biotic associations are important for plant survival.

Ecological and ecophysiological patterns in a pre-altiplano shrubland of the Andean Cordillera in northern Chile

We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (Δ) of 3.7–7.5‰ through C3 species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of ci:ca ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities.

Plant community variation across a puna landscape in the Chilean Andes

Describimos los patrones de abundancia de las especies vegetales y las formas de vida en la vegetacion de puna en el Parque Nacional Lauca, Chile. A una altitud que excede los 4.300 m de altitud, el habitat extremo de nuestro sitio de estudio presenta relativamente pocas especies. Dichas especies, sin embargo, representan un arreglo diverso de formas de vida organizadas con respecto a distintos gradientes ambientales. Tanto la riqueza de especies como el habito de crecimiento aumentaron en los suelos mas rocosos y en las pendientes expuestas al norte y al este, cuya vegetacion es mas xerofila. Dichos sitios presentaron la mayor abundancia en formas de cojines. Los sitios menos rocosos con un suelo mas desarrollado presentaron una mayor abundancia de pastos y arbustos. Distintos microhabitats fueron ocupados por especies congenericas que con frecuencia divergieron en su habito de crecimiento. Los patrones observados sugieren que el agua y el estres termico son fuerzas criticas que moldean la forma funcional de las especies vegetales asi como la organizacion de las comunidades de plantas en la puna altoandina