Analysis of interspecific competition in perennial plants using life table response experiments

The impact of interspecific competition is usually measured by its effect upon plant growth, neglecting impacts upon other stages of the life cycle such as fecundity which have a direct influence upon individual fitness and the asymptotic population growth rate of a population (lambda). We used parameterized matrix models for three perennial plant species grown with and without interspecific competition to illustrate how the methodology of Life Table Response Experiments (LTRE) can be used to link any change in population dynamics to changes in any part of the life cycle. Plants were herbaceous grassland species grown for two years in a field experiment at Rothamsted Experimental Station, England. Interspecific competition reduced X by over 90% in all species. Survival and growth were slightly affected by competition whereas plant fecundity was greatly reduced. Nearly all of the observed difference in X between the competition treatments was explained by the fecundity terms, and more precisely by a large difference in the number of seeds, and a high sensitivity of X to the germination rate. Whereas most competition studies focus on the measurement of change in individual fitness, our study illustrates how informative it is to take account not only of the effect of competition upon vital rates but also of how different vital rates affect population growth rate

Seed dispersal of Solanum thomasiifolium Sendtner (Solanaceae) in the Linhares Forest, Espírito Santo state, Brazil Dispersão de sementes de Solanum thomasiifolium Sendtner (Solanaceae) na Floresta de Linhares, Espírito Santo, Brasil

The aim of this study was to analyse seed dispersal and establishment of Solanum thomasiifolium in an area of "nativo" vegetation in Espirito Santo state on the southeastern Brazilian coast. Ten species of birds, the crab-eating fox (Cerdocyon thous), and one species of lizard (Tropidurus torquatus) fed on S. thomasiifolium fruits and dispersed viable seeds in their faeces. The proportional contribution of each of these groups to seed dispersal was 77% (birds), 19% (crab-eating fox) and 4% (lizards). Ants also contributed to seed dispersal. More seeds were deposited in vegetation islands than in the surrounding open areas. Germination rates of seeds collected directly from fruit (control), bird droppings, the faeces of crab-eating foxes and lizards were, respectively, 64, 64, 53, and 80 %. Differences among these rates were all significant, except between birds and control. Lizards were important as seed carriers between nearby islands and they expelled a higher proportion of viable seeds. Birds and the crab-eating foxes did not enhance seed germination, but promoted seed dispersal over a wider area. Plant architecture, fruit productivity, fruit characteristics and the diversity of frugivores are important for the success of S. thomasiifolium in habitat colonization.<br>O propósito deste estudo foi analisar a dispersão de sementes e o estabelecimento de Solanum thomasiifolium em uma área de vegetação de "nativo" no Estado do Espírito Santo, na costa do sudeste do Brasil. Dez espécies de aves, o cachorro-do-mato (Cerdocyon thous) e uma espécie de lagarto (Tropidurus torquatus) alimentaram-se de frutos de S. thomasiifolium e dispersaram sementes viáveis em suas fezes. A contribuição proporcional de cada um destes grupos na dispersão de sementes foi de 77% para aves, 19% para o cachorro-do-mato e 4% para o lagarto. Formigas também contribuíram com a dispersão de sementes. Mais sementes foram depositadas nas ilhas de vegetação do que nas áreas abertas vizinhas. As taxas de germinação de sementes oriundas de frutos (controle), fezes de aves, fezes do cachorro do mato e do lagarto foram, respectivamente, 64 %, 64 %, 53% e 80%. As diferenças entre estas taxas foram todas significativas, exceto entre o controle e fezes de aves. Lagartos foram importantes como transportadores de sementes entre ilhas de vegetação próximas e defecaram uma grande proporção de sementes viáveis. As aves e o cachorro-do-mato não aumentaram a germinação de sementes, mas promoveram a dispersão sobre uma área maior. A arquitetura da planta, a produtividade de frutos, as características do fruto e a diversidade de frugívoros são importante no sucesso de S. thomasiifolium para colonização do habitat