Insect herbivores, density dependence, and the performance of the perennial herb Solanum carolinense.

How insect herbivores affect plant performance is of central importance to basic and applied ecology. A full understanding of herbivore effects on plant performance requires understanding interactions (if any) of herbivore effects with plant density and size because these interactions will be critical for determining how herbivores influence plant population size. However, few studies have considered these interactions, particularly over a wide enough range of densities to detect nonlinear effects.

Intraspecific competition facilitates the evolution of tolerance to insect damage in the perennial plant Solanum carolinense.

Tolerance to herbivory (the degree to which plants maintain fitness after damage) is a key component of plant defense, so understanding how natural selection and evolutionary constraints act on tolerance traits is important to general theories of plant-herbivore interactions. These factors may be affected by plant competition, which often interacts with damage to influence trait expression and fitness. However, few studies have manipulated competitor density to examine the evolutionary effects of competition on tolerance.

Leaf herbivory and drought stress affect floral attractive and defensive traits in Nicotiana quadrivalvis.

Adaptive phenotypic plasticity allows sessile organisms such as plants to match trait expression to the particular environment they experience. Plasticity may be limited, however, by resources in the environment, by responses to prior environmental cues, or by previous interactions with other species, such as competition or herbivory. Thus, understanding the expression of plastic traits and their effects on plant performance requires evaluating trait expression in complex environments, rather than across levels of a single variable.

Sources and consequences of seed size variation in Lupinus perennis (Fabaceae): adaptive and non-adaptive hypotheses.

Seed size variation within species and individuals is common. This variation may be adaptive in heterogeneous landscapes if the fitness consequences of seed size differ among environments or through time. Variation may also arise from constraints that limit control of seed size.

The evolution of androgenesis.

It is well known that some species produce offspring carrying only female chromosomes by processes such as apomixis and parthenogenesis (generically termed "gynogenesis"). There are also several cases of natural reproduction by androgenesis in which diploid offspring carry nuclear chromosomes from only the male parent. We used population genetics models to investigate the conditions for invasion of rare androgenesis alleles and the consequences of their spread.