In this last IBDP Biology ecosystem blog post, we will look at:
- Sustainability of ecosystem
- Chi squared test
- Quadrats
Ecosystem Sustainability
To remain sustainable an ecosystem requires:
- Continuous energy availability:
Light form the sun
- Nutrient
cycling: Saprotrophs are crucial for the continuous provision of nutrients to producers
- Recycling
of waste: Certain products of metabolism are toxic [Ammonia from excretion]. Deccomposing bacteria absorb the toxic molecules as
- Energy,
breakdown and release less toxic molecules
Mesocosms
Mesocosms: Biological systems that contain the abiotic and biotic features of an ecosystem, but are resticted in size and under controlled conditions
Mesocosms are useful for scientific investigations because natural ecosystems prove harder to collect valid data from
- 5 Litre clear glass jar
- Seal to prevent entry/exit of chemical substances
- Air containing
Oxygen and Carbon Dioxide
- Pond water containing Autotrophs, Consumers, Detrivores and Saprotrophs
- Mud
from bed of pond
- Autotrophs: Produce carbon compounds and regenerate oxygen used in cell respiration by organisms in mesocosm [essential]
- Saprotrophs:
Decompose dead organic matter and recycle nutrients [essential]
- Consumers and Detrivores: Usually included, unethical to include large organisms that cannot obtain food or enough oxygen [non-essential]
Testing for Association between Species
- Positive
Association: Species found in the same habitat
Example: Preditor and prey [symbiosis]
Herbivore and plant
- Negative
Association: Species occur separately in different habitats
Example: Competitive exculsion as they require different nutrients
- No
Association: Species occur as frequently when they are apart as when they are together
Quadrats
- Quadrat sampling can be used to:
- Estimate
population density/size
- Measure distribution of species
- Placed
repeatedly in sample area to provide a reliable estimate
- Placed systematically to
measure changing distribution
- Placed
randomly to estimate popluation density [presence/absence, frequency or % coverage]
- Systematic and Random Sampling are used to avoid bias in the selection of sample
- Limitation
: Large and mobile animals cannot be effectively sampled.
- Most suitable for plants and small slow-moving animals
Chi-squared Test
1. Always define Hypotheses
Null Hypothesis: There is no significant difference between the distribution of two species [distribution is random]
Alternative Hypothesis: There is a significant difference between the distribution of species [species are associated]
2. Complete the contingency table of observed frequencies using the data
3. Calculate the expected values using the formula
expected values: (row total x coloumn total over grand total)
Expected values: Expect to find if there is no association between the species
4. Calculate the chi-squared value
5. Determine the degrees of freedom - if species are associated df is always 1
(rows - 1) x (coloumns - 1)
6. Compare x squared value with the critical values and validate the hypotheses
df = 1 H0 [Null hypothesis is rejected and H1 is accepted that there is an association between the two species
That is the end of this subtopic! Well done!!
Part 1: https://www.tuttee.co/blog/ibdp-biology-species-communities-and-ecosystems-1-3
Part 2: https://www.tuttee.co/blog/ibdp-biology-species-communities-and-ecosystems-2-3
Drafted by Venetia (Biology)