Patterns in abundance and seasonality of insects in the siruvani forest of Western ghats, nilgiri biosphere reserve, southern India.

P R Arun,V S Vijayan

doi:10.1100/tsw.2004.33

Abstract

The seasonal abundance patterns of insects inhabiting the understory vegetation of a mixed deciduous forest were examined with the help of the sweep-net sampling method. During the study period of 2 years, insects were sampled regularly from the understory vegetation of the three selected habitats (moist-deciduous, riverine, and teak plantation) of the mixed deciduous forest. Insect abundance was maximum in the moist-deciduous habitat and minimum in the teak plantation. Generally, insect abundance was the highest during the southwest monsoon in all habitats. The temporal pattern of fluctuations in the insect abundance followed more or less the same pattern in all the three habitats studied. The insect abundance of the understory vegetation varied among the habitats studied, while the pattern of seasonal fluctuations in insect abundance was comparable among habitats. Composition of the insect community also indicated prominent seasonal changes within habitats than interhabitat changes within a season.

Highlights

Seasonal variation in the abundance of a species is an adaptive phenomenon evolved to take maximum advantage from the ambient environmental conditions
Apart from the primary genetic programming, environmental conditions that involve both density-dependent as well as density-independent factors play an important part in insect seasonality
The present paper examines any direct relation between the fluctuations in insect abundance with abiotic environmental parameters such as rainfall, temperature, and humidity

Summary

Introduction

Seasonal variation in the abundance of a species is an adaptive phenomenon evolved to take maximum advantage from the ambient environmental conditions. Presence of distinct larval and imago stages, which differ from each other in many ways, including the feeding mechanisms and even the ecological niche, is a characteristic feature of holometabolous insects. Equipped with the diverse modes of lifestyles and ecological requirements during different life stages, the insects have got an edge over most other organisms in resource utilization potential. One of the major factors on which their success and survival depends is how efficiently they time their lifecycle so as to utilize the maximum resources and environmental conditions. Apart from the primary genetic programming, environmental conditions that involve both density-dependent as well as density-independent factors play an important part in insect seasonality. Density-dependent factors are responsible for regulating the population about its average level of abundance, while the density-independent factors, such as climate and weather, can cause catastrophic changes in the abundance either by enhancing the mortality rate or by triggering a change in

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Conclusion