4. Discussion

               From the data collected, it was clearly found that dragonflies were more likely to be found in areas that were more disturbed or open while damselflies were more likely to be found in shaded streams as shown in Table 2. The higher Dissolved Oxygen values and predators also favoured the damselflies rather than dragonflies as described by McPeek (2008). The development of morphological defence mechanism strategies such as longer abdominal spines in damselfly larval stages are believed to reduce the level of predation by fishes. Dragonflies on the other hand, are more likely to be found in stagnant water bodies devoid of predators such as fishes. (McPeek, 2008). There is however, an exception in Stream He, where the low levels of DO does not affect the damselflies population adversely.

            Water quality parameters such as high dissolved oxygen levels of at least 5.71 mg/L suggest that some odonates such as Tyriobapta torrida  has a preferred physiochemical habitat while others like Vestalis amethystinna could be found in varying levels of dissolved oxygen. The most obvious was the case at the Stream Hd, where almost all species collected were dragonflies. It seems that dragonflies have developed strategies to thrive in turbid waters that are devoid of predators such as fishes as an evolutionary mechanism against predation as proposed by McPeek (2008). Hence Dragonflies and Damselflies adopted different strategies in evolutionary development against predation.

            Generally, by selecting specific features of different dragonflies and damselflies, we can use them as indicators of ecological health of water resources in our catchment areas based on this initial baseline study. The distribution map developed can be used to make deductions about the odonates as a bio-indicator for ecological health of freshwater resources in the Upper MacRitchie Basin.

In stream Ha, no odonates were collected. This could be attributed to the degraded stream environment at the headwaters of the stream Ha as observed by the investigator. In 2000, a landslide at the headwaters of stream Ha could have changed the habitat. However, there were no significant water quality parameters that indicated any significant stress factors except for a low dissolved oxygen levels in stream Ha. The absence of odonates could be used as an indicator of environmental stress rather than poor water quality, which is a limitation of this method.