C4.1 - tests for interspecific competition (1g)

Question 1

what are 3 methods to test for interspecific competition?

Answer 1

1. laboratory experiments
2. field observations by random sampling
3. field manipulation by removal of one species

Question 2

how can laboratory tests be used for interspecific competition?
what are the pros and cons?

Answer 2

taking organisms out of their natural environment and growing them in a lab to measure the impact on growth
pros - can control more variables, improving validity
cons - this isn’t ethical, so is only done on common plant species

Question 3

how can field observations be used for interspecific competition?
what are the pros and cons?

Answer 3

observing two species in an area and determining whether they are present in the same locations at the same time, can inform us of potential competition
pros - minimal or no disturbance to ecosystem
cons - only naturally occurring phenomena can be researched as conditions not manipulated

Question 4

how can field manipulation be used for interspecific competition?
what are the pros and cons?

Answer 4

researchers measure population of second species before removing the first and measuring the population of the second species afterwards
pros - allows a causal relationship to be determined
cons - ethical concerns as the ecosystem and other species will be disrupted

Question 5

what is the difference between observations and experiments?

Answer 5

observations - measure value of a factor that naturally changes

experiments - manipulation of a factor to determine the effect

Question 6

what is a chi-squared analysis used for?

Answer 6

explores the similarities or differences in the distribution of two species across several sampling sites
- this may provide evidence for interspecific competition

Question 7

what is a positive association?

Answer 7

if two species are typically found in the same areas, they show positive association
- e.g) those in a predator-prey relationship, or symbiotic relationships

Question 8

what is a negative association?
what are the 2 types?

Answer 8

if two species tend not to occur in the same areas, they show negative association
- (eg) competitive exclusion = one species may use the resources more effectively, outcompeting the other, which cannot survive
- (eg) resource partitioning = both species change how they use the habitat, to avoid direct competition

Question 9

what is no association?

Answer 9

if two species do not interact, there will be no association and their distributions will be independent.

Question 10

how can we used the chi-squared test for the association between 2 species?

Answer 10

1. place quadrats throughout the area of study
2. in each quadrat determine the presence or absence of each species (observed values are recorded in a matrix)
3. the null hypothesis is that the presence of one species is independent in relation to the presence of the other species, and the alternate hypothesis is that the presence of one is associated with the presence or absence of the other
4. calculate the expected values using the product of the row and column totals, divided by the grand total
5. use the formula to calculate a chi-squared value
6. data interpretation

Question 11

what does it mean if the calculated chi-squared value is larger than that in the table of critical values?

Answer 11

• the difference between observed and expected is statistically significant (p<0.05)
• the null hypothesis is rejected and the alternative hypothesis is accepted
• the data supports the association between the two species