Effects of Water Flow Speed on the Abundance of Individuals of Animal Species Ko Chin Wa Tsang Faan Ho Wong Hin Ching

Variables Independent variable - speed of water flow Dependent variable - abundance of individuals of animal species Controlled variables - water depth (shallow), river bed substrate composition (pebbles and small stones), time for sampling at each location (approximately 20 minutes), number of people sampling (2)

Hypothesis Number of individuals rises for slowly flowing water, until the optimum flow speed is reached, then the number of individuals starts to fall for fast flowing water.

Materials and Methods Designate three shallow regions (for easier sampling) that have roughly the same river bed substrate composition (pebbles and small stones) with different water flow rates. A water flow meter - measure the water flow speed A stop watch - measure the time for collecting samples and ensure a fair test by using the same time at each location A 0.5m x 0.5m quadrat - sample as many animal species within the boundary of the quadrat as possible, within 20 minutes Pick up the stones to see any hidden species Identify the species and make a table for counting the number of individuals

Results

Blue - Viviparous Snail Green - Water Skater Yellow - Water Penny Red - Damselfly Nymph Purple - Mayfly Nymph Orange - Dragonfly Nymph

Still water

Water flowing at moderate speed

Fast flowing water

Analysis and Summary Water flow speed rises for slowly flowing water Still water has no appreciable current Oxygen concentration is low Water turbidity is high Limited source of nutrients A rise of water flow rate leads to better environment for survival

Analysis and Summary The number of individuals reach a peak at optimum water flow rate Usually saturated with oxygen More available food

Analysis and Summary Number of individuals of not-so-adaptive species start to fall Species having developed adaptive features, e.g. viviparous snail, for fast running water will benefit from less severe interspecific competition and have a much larger number of individuals