THE DISTRIBUTION AND ABUNDANCE OF DRAGONFLIES IN NATURE RESERVES IN ESSEX
Student name: Michelle Garrett
Supervisor: Alastair Grant
Keywords: Ecology
Year submitted: 1993
Abstract:
The distribution and abindance of Odonata was studied within and between three nature reserves in Essex, chosen because of their diversity of habitats and different waterbody types. The objective was to determine whether there was any significant difference in Odonata species and numbers between these sites, and if so, whether this could be explained by habitat type, and/or waterbody type and quality.
The importance of the sites studied was assessed using Odonata species distribution and abundance as an indicator, with particular reference to those species recorded as being in decline.
Counts of observed Odonata were undertaken over a four week period. Water quality at the three sites was determined by testing the chemical parameters of pH, phosphorus and nitrate to determine whether this could be a limiting factor for influencing the abundance of Odonata. An assessment of vegetation was made at each habitat with regard for possible oviposition, emergence, and shelter sites.
There was a significant difference in total Odonata numbers between the three sites. When observing each species separately there was a significant difference in abundance of individuals between each habitat within the three sites.
Different Odonata species have their own individual habitat requirements, which could explain the difference in distribution and abundance of the species observed between the habitats and sites. The variation in the water quality parameters could also have an influence. In a wider context the length of time the reserves have been established, and their size and surroundings could be an explanation.
The importance of habitat conservation has been highlighted by the study, with the emphasis on the maintenance and management of aquatic habitats, to protect Odonata species from further decline.
