Analysis of Insect Trophic Diversity in Two Salt Marsh Communities

This study analyzes tropic relationships of the insect components of two intertidal salt march communities dominated by Salicornia pacifica and Spartina foliosa, respectively. Seasonality of that component is determined and influence of physical microenvironmental factors on trophic diversity is assessed. Adult insect populations were monitored weekly, trophic diversity was computed, and relationships with primary production and litter accumulation were quantified. Temporal diversity trends were similar in both communities although the amplitude was slightly greater in Salicornia. In both communities, herbivore diversity was highest during the spring months while saprovore diversity was highest during midwinter. Predator diversity responded to both herbivore and saprovore diversity, although it was more closely tied to herbivore fluctuations in Salicornia. Standing crop biomass was maximum during October and litter accumulation was highest during Janurary. Two classes of adult insects occurred: peristent species, representing a low percentage of the total species compliment, were present as adults throuhout the year in both marsh communities; seasonal species, on the other hand, were present as adults only during the growing season. Seasonal succession in species of herbivores and saprovores reflected productional and transformational changes in plant matter; predators responded likewise, but more impressive was the numerical response to prey populations by particular predators. Correlations were high between each trophic group and its respective resource. Physical microenvironmental factors, especially temperature and vapor pressure deficit, seemed to be important in cuing larval development, but did not exert a dramtic effect on adult diversity trends. Several strategies of habitat utilization are considered. It is hypothesized that the persistent and seasonal species have evolved as specialists to avoid competitive interactions and maximize resource utilization. During annual expansion of resource states, the salt marsh insect component undergoes speices packing wherein additional species enter the system temporarily to utilize the expanded resource base.