Effects of Water Flow Speed on the Abundance of Individuals of - PowerPoint PPT Presentation

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

Results Blue - Viviparous Snail Green - Water Skater Yellow - Water Penny Red - Damselfly Nymph Purple - Mayfly Nymph Orange - Dragonfly Nymph 12 9 6 3 0 Still water (~0 m / s Moderately flowing water (~0.02 m / s) Fast flowing water (~0.18 m / s)

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