California Sea Grant College Program

There are a wide variety of ecological and genetic factors that influence the rate of population growth. As an invading species changes its habitat, varying selective regime may change it in turn. Spartina alterniflora Loisel has been introduced around the world and is a clonal estuarine weed of both environmental and economic concern. Recruitment by seed is a relatively uncommon event in the native range of this plant where fitness is enhanced by vegetative persistence. Invaded regions provide an essentially unoccupied niche facilitating rapid propagation by seed. The invaded community and the source location may differ in selective pressure leading to a distinct response trajectory in the invader. Genetic adaptation can occur as a result of intrinsic ecological selective pressures, including Allee effects, reduction of some component of fitness with decreasing population density, and low genetic variability. This wind-pollinated exotic suffers from an Allee effect, caused by pollen limitation. The Allee effect reduces fecundity at a more than a ten-fold magnitude at low density, contrasting with the competitive, highly dense nature of the native range. Knowledge of density effects is a critical, though often omitted, requirement for empirical testing of much life-history evolution theory. Changes in life history traits following selection can then affect the rate and characteristics of population growth. I found the invader to have much greater reproductive effort, initiate reproduction both younger and smaller, has a greater risk of death with greater reproductive effort and to have greater self-compatibility than natives. The study of the interaction of biology and life history evolution of an invading organism with the ecology of the recipient community provides an opportunity to address the consequences to subsequent population expansion.

Additionally, we assessed pathogen-vectoring risks of a planthopper, Prokelisia marginata, proposed as an agent of biological control. We identified a list of possible pathogens and amplified sections of bacterial DNA and sequenced the fragments to assay whether bacterial DNA extracted from both plants and insects, is potentially pathogenic. We found no evidence of transmissible pathogens but found that putatively specific PCR primers for Pseudomonas bacteria amplified a variety of other bacteria.