Most of the weeds found in this study are dominant because they are all aquatic and lowland weeds that benefit from the closeness of the area to a river. The change in the habitat from swampy to sandy soil contributed to the transition from exclusively a mangrove community to a weed community. Loss of mangrove forest as a result of anthropogenic action lead to a loss of the ecosystem services they provide e.g. carbon sequestration, fire wood and basket production and fisheries. The weed are not known to provide any significant ecosystem services to the environment apart from being host to some disease parasites, causing bush fires and acting as a nuisance in the environment. The species Mariscus longibracteatus are more dominant because they are aquatic weed that grow in wet grounds in forest zones. They are of the family Cyperaceae . They are large tufted sedge that can grow to about 1 m, and are produced from seeds. Their seeds are tiny and are propagated by wind. They have very prominent spikes on an inflorescence, which sticks to clothing and facilitates dispersal and propagation.
This has made them to be found in any environment. Although they are mangrove forest plants, but are introduced through human activities such as logging, sand filling, construction and reclamation. High concentration of Zn can be ascribed to increased land runoffs and influx of metal-rich water in the weed root soil giving rise to elevated metal levels. Similarly, elevated levels of metals in weed root soil were observed in Pondicherry Harbor . However, it was found that the total concentrations of all selected heavy metals in the weed root soil were below the critical soil concentration values , which reflect the topography and bed rock of the area as the origin of these metals. Several studies of plant phenology and insects have focused on the relationship between plants and the life cycle or population dynamics of phytophagous insects.Published studies on the influence of plant phenology on carabid beetles have examined the consumption of weed seeds by carabid species,grow lights for cannabis as well as the role of weeds as a refuge and dispersal aid for carabids in agroecosystems There are also reports of weedy plants causing changes in the carabid community structure Feeding habits of carabid beetles range from carnivory to phytophagy, but there are also carabid species with more-specialized feeding behaviors .
For example, in terms of phytophagy, carabids can be classified into two groups: 1) those that are carnivorous but supplement their diets with vegetation; and 2) those that are seed consumers Thus, in addition to being recognized as important biological control agents of crop pests, carabids are also an important group of seed feeders and, thus, can act efficiently to reduce the size of weed populations in agroecosystems Carabids and crickets dominate the granivorous taxa of temperate regions whereas ants are dominant in the tropics . Among the carabid beetles, the Harpalini and Zabrini tribes contain the most granivores Despite the rich carabid fauna in Brazilian agroecosystems there are no specific studies from this region on carabid beetles as weed seed consumers or on their relationship with the phenological stages of weedy plants. The only studies published on the feeding habits of Brazilian carabids were by Barbosa et al. , who evaluated the effect of different diet types on biological aspects of two carabid species, and Matta et al. , who determined the types of food within the digestive tract of carabids associated with herbaceous plants and colored cotton.
It is also worth noting that the life cycle of Brazilian carabids inhabiting agroecosystems is almost unknown; however there is information available about seasonal activity of several dominant carabid species in the state of São Paulo . Therefore, in the current study, a survey of adult carabids was carried out in the edge habitat covered by weedy plants and located between a forest fragment and a soybean/corn crop or an orange orchard in five sites in northeastern São Paulo state, Brazil. The objective was to determine the changes in the density of carabid species in relation to different phenological stages of weeds. We considered the increased number of individuals of a carabid species during the reproductive stages of weedy plants, an indication of preference to feed on seeds of agricultural weeds.