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Flashcards in Lecture 5 - ghost crabs Deck (13)
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1

what is ecology?

> the study of the interaction that determine the distribution and abundance of organisms
>

2

what are interactions?

> between organisms and their abiotic
> between organisms and others of the same species
> between organisms and others of different species

3

what is the distribution of organisms like?

> scale dependent
> random
> uniform
> clumped

4

what is dispersion?

> the pattern of spacing of individuals within a species
> random:
- position of individuals is random with respect to each other
>uniform, over-dispersed, hyper-dispersed, regular - further apart than 'expected'
> under-dispersed, clumped, aggregated - closer together than 'expected'

5

what are some biological reasons behind dispersion patterns?

> random
- when positions of individuals are not affected by others (often used as a null model or expected)
> uniform
- individuals avoid contact or die if they are close (intra-specific competition)
> Clumped
- benefit from contact or use same habitat, resources, herd

6

what is a good test to do to measure level of distribution?

> if the number of individuals in 'plots' are randomly distributed then the frequency distribution of these counts, x, will follow a poisson distribution (with lambda = mean = variance)

7

what is an example of how to calculate distribution with crab holes?

> compare actual number of quadrats with x crabs holes with expected number calculated using a poisson distribution
> if actual and expected distributions are similar then crab holes are randomly distributed in the sample guadrats

8

what is a simpler way to analyse dispersion? (not poisson)

> variance is a measure of the spread of a set of values about its mean
> variance = sum of (xi - mean) squared / (n-1), where xi is a measure of the variable, n is the number of measures
> for poisson distribution the variance = mean

9

what are Nearest neighbour distances?

> for Random, distance between a randomly chosen individual and its nearest neighbour should be the same as the distance between a random point and the nearest individual
>for clumped, NN distances will be smaller than random point

10

what is sampling theory?

> how many are there? estimating population size, p
> known area A? known density D (numbers per unit area), then P=DxA
> take n small areas each of area a, count or census xi in each and estimate density D, D= sum of xi/n

11

how do you select quadrat locations, and what are some sampling techniques?

> systematic
- easy, but can be biased
> simple random sampling
- proper random samples are hard to take
- random = haphazard
- need a map, random number table and gps
> stratified random sampling
- good if you know there are high density and low density patches and you can map them
- sample separately, combine estimates later
> cluster samples
- efficient and good for removing unconscious bias
- but sample size is number of clusters

12

how do you work out how many samples to take?

> balance of precision vs cost
> sampling error = 2x standard deviation / sqrt(sample size)
> but standard deviation is not known in advance
> sample size of >15-20 allows large sample statistics to be applied
> doubling precision requires 4 times sample size

13

what are the two types of sampling methods?

> line transects
> point transects
> only a portion of organisms are detected, Pd
> the D = (n/2wl)Pd
> Pd can be estimated from distance data. this is critical