In-class Activity 10 Population Fluctuation and Structure Group ______________
__________________ _________________ _______________ ______________
Fluctuation in Population Size through Time….
1. What are three general reasons that populations fluctuate around equilibrium?
A.
chance
B. environment changes
C. intrinsic dynamics
2. In population models, how does the value of r affect the pattern of oscillation around
K? r =<1 follows logistic curve; r 1<2 damped oscillations; r >2 limit cycle
r>>>2 chaos
3. How will fluctuations affect a population’s age structure?
They will change the structure if different ages react differently in terms of b and d
in response to the cause of the fluctuation.
With fluctuation, is a stable age distribution reached quickly, slowly, or possibly
never? Slowly or not at all, if fluctuation is recurrent.
What are the consequences for the population growth rate if the age structure is not
stable? It is inconsistent; fluctuates eratically.
4. Can a population crash lead to no recovery? Sometimes
Why? What happens if population density gets too low that prevents recovery?
At too low a density, individuals may not be able to have critical social interactions,
including mating or defenses against predators. Undercrowding may be
harmful to social species.
5. What are the consequences of a time lag (delay) in adjustments of birth and/or death
rates to a change in population density?
The population size may not follow a smooth path of logistic growth.
The momentum of the birth rate may push the size above K.
Survival above K may drop sharply.
What are two reasons why a population may have a time lag?
A. development time is long (and is completed long after environment changes)
B. nutrient storage isolates individual from change in the environment
6. If fluctuations are synchronized among similar species in a community, are the
organisms likely to responding to a common external or intrinsic cause? External
7. Why type of organism shows less fluctuation? large, long-lived or small, short-lived?
Why? Large, long-lived organisms have greater homeostatsis and overlapping
generations that buffer any response of b and d to envivornmental changes
8. What two factors change as a population ‘self-thins’ (e.g. plants or fish)?

density decreases and biomass increases
What causes self-thinning to arise? Resource limitation. Competition increases
as individuals get larger and some die, thus reducing the density.
Variation in Population Abundance across Space
1. What are the problems determining the abundance of a clonal plant?
Underground connections are invisible. May count each above-ground stem
as a unique individual, while, in fact, it is a ‘branch’ (ramet) of one individual
(genet).
2. Is size a good indicator of age in plants? No Why/Why not?
Plant size is very plastic and responsive to the external environment. Two individuals
of the same age can have very different sizes if they experience different conditions.
3. What method did we use to estimate population size of small mammals in our lab? mark-recapture
4. What is meant by distribution?
density? # individuals per unit area (e.g. # treefalls per 50 m2 quadrat)
dispersion? spatial pattern of a group of individuals
5. What type of species tends to spread their range quickly? invasive species
What factors affect the geographic distribution of a species? phenology, dispersal, behavior (habitat selection), interactions with other species,
abiotic factors, human introductions, change, history
6. Are ranges typically small or large? small
How does range size change with increasing latitude? increases
What is one possible reason? Temperature fluctuations increase with latitude. An
species that can tolerate wide fluctuations at one place can survive over a wide area.
7. What is the relationship between range and abundance? positive
8. Do large or small vertebrates tend to have greater density? small
At a given body mass, do birds or mammals have greater density? birds
What is one possible reason? Birds with a higher metabolic rate than mammals
require more food and hence have greater territories, thus reducing density.
9. What are two factors causing a plant population to be clumped? habitat heterogeneity; dispersal limitation; vegetative reproduction
What additional factor may affect an animal’s dispersion? social interactions, e.g. territoriality