Community dynamics and diversity of ground dwelling arthropods assemblages in a maize based agroforestry system in Mtwapa, coastal Kenya
Kamunya, Esther Wairimu
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The effect of diversification and intensification in agro ecosystems to arthropod diversity is not well understood, mainly because conservationists have greatly ignored agro ecosystems, while most of the research work has been for a long time, directed towards the so called undisturbed systems like the natural forests. This study was intended to contribute towards evaluating relationships in agro ecosystems and to assess the impacts cropping systems on the diversity and dynamics of soil dwelling arthropods. During the first phase of this study, Pitfall trapping was conducted every two weeks in all the plots from June 1999 to February 2000 and the arthropods collected classified to family level. Treatments consisted of different crop combinations and practices involving alley cropping and intercropping of maize, cowpea, Leucaena, and Gliricidia (mlgc), mulching (mu) and use of pesticides (p). An additional unmanaged field (um) was sampled for comparison with the managed agro ecosystems. This gave a total of eleven treatments in 1999-2000 cropping seasons (June 1999-February 2000). During the 2000-2001 (June 2000-February 2001) cropping seasons two additional sole cowpea treatments, one of which was treated with pesticides, (c and c+p) were sampled. Pitfalls were served weekly instead of fortnightly as in the previous seasons and arthropods identified further to Genus and species level where possible. Thereafter, Shannon Weiner (H') and Simpson-Yule (D) diversity indices, evenness (J) and species richness (S) were calculated for all the plots. The data obtained was then subjected to analysis of variance to test for treatment differences. A total of 8,184 arthropods belonging to 20 families were collected during the long and short rains of 1999-2000. The family Formicidae was the most abundant accounting for 84.34% of the total samples. The unmanaged system (um) and the maize intercropped with leucaena, gliricidia and cowpea (mlgc) had the highest Species richness (S=8.25), for both treatments). There was a significant difference (P<0.05) only in evenness with (um) being significantly different from all the others, and the maize monocrop (m) being significantly different from maize+cowpea (mc). During the long and short rains of 2000-2001 a total number of 146 958 arthropods were collected belonging to the five major orders in the samples, namely Hymenoptera, Coleoptera, Orthoptera, Blattoidea and Aranae. Of the five orders, the order Hymenoptera was the most abundant (78.44%). A total number of 70 different species representing 26 families were identified. Species richness (S) was not significantly different (P>0.05) between treatments. However species diversity (D and H') and evenness (J) was significantly different (P<0.05) between treatments, with the unmanaged system recording significantly greater diversity that all the other treatments. Orthogonal contrasts however indicated that this difference was not significant between the unmanaged plots and some plots with agro forestry tree species, while it was significant in the other treatments. There was low species diversity in treatments in which pesticides were applied as well as those without mulch as compared to the mulched.
- MST-Zoological Sciences