Spatial Relationships

What is dispersion in spatial ecology?

distribution of individuals within a population (how they are arranged in space)

What is clumped dispersion?

• distance between individuals is minimized

• most common dispersion

• patchy resources, limited dispersal of juveniles, herding animals, avoiding predation, etc.

What is uniformed/even dispersion?

• distance between individuals are maximized

• occurs when there is strong competition for resources

• more common than random dispersion but less common than clumped dispersion

What is random dispersion?

• individuals are located in random locations

• least common dispersion

• may occur in homogeneous environments, when individuals neither attract or repel one another or when there’s little data

How can changing spatial and temporal scales influence the dispersion pattern observed?

• clumped patterns at a large scale may appear uniform at a smaller scale

• seasonal changes or life stages can also influence dispersion patterns over time

What is the Clark-Evans nearest neighbor method and how does it determine the dispersion pattern of a population?

• calculates the average distance between each individual and its nearest neighbor

• average is compared to the expected average distance in random dispersion (ratio is R)

• R >1 = uniform

• R <1 = clumped

• R close to 1 = random

What is the variance/mean ratio test and how does it determine the dispersion pattern of a population?

• calculating the mean number of individuals in a sample plot and compare results with an expected randomly dispersed sample

• a ratio >1 = clumped

• a ratio <1 = uniform

• a ratio close to 1 = random

What is the interspecific association test and how does it determine whether two species are associated with one another?

• measures whether the presence of one species is correlated with the presence of another using the contingency x² test

• positive association - two species tend to be disperse near each other

• negative association - two species tend to be dispersed away from each other

How do you use a t-distribution/chi-squared table to find a p-value range when given a degree of freedom and a t-value?

• Locate the row corresponding to the given degree of freedom, then find the column where the t-value falls

• the p-value range is identified based on the overlap between the data and the table

When given a p-value and alpha-value, how do you determine whether to reject or fail to reject the null hypothesis?

• if p-value is less than or equal to the alpha value = reject the null hypothesis

• if p-value is greater than the alpha value = fail to reject the null hypothesis