1. Population Ecology Ch. 9

2. Population Ecology Outline
9-1: Population Dynamics and Carrying Capacity
9-2: Reproductive Patterns and Survival
9-3: Effects of Genetic Variations n Pop. Size
9-4: Human Impacts and Working with Nature
Bozeman videos:
Population Ecology
Logistic Growth

3. 9-1: Population Dynamics and Carrying Capacity
Population - individuals of the same species, inhabiting the same area at the same time.
Population Dynamics: Population change due to
Population Size - number of individuals
Population Density - population size in a certain space at a given time
Population Dispersion - spatial pattern in habitat
Age Structure - proportion of individuals in each age group in population

4. Population Density
Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area
Some species exist in high densities - Mice
Some species exist in low densities - Mountain lions
Density depends upon:
social/population structure
mating relationships
time of year

5. Population Dispersion
Population dispersion is the spatial pattern of distribution. There are 3 main patterns of dispersion:
Clumped: individuals are
lumped into groups
ex. Flocking birds or
herbivore herds due to
resources that are clumped
or social interactions;
most common

6. Population Dispersion
2) Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals.
3) Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met
tips/2002/clover611.htm

7. Age Structure
The age structure of a population is usually shown graphically.
The population is usually divided up into
Prereproductives (not mature enough to reproduce)
reproductives (capable of reproduction)
Postreproductives (too old to reproduce)
The age structure of a population dictates whether is will grow, shrink, or stay the same size.

8. Age Structure Diagrams
Positive Growth Zero Growth Negative Growth
(ZPG)
Pyramid Shape Vertical Edges Inverted Pyramid

9. Limits to Pop. Growth
Biotic Potential- Ability of populations of a given species to increase in size
Abiotic Growth Factors (can affect biotic potential)
Favorable Light conditions
Favorable Temperatures
Favorable Chemical environment – optimal levels of nutrients
Biotic Growth Factors:
High reproductive rate
Generalized niche
Ability to migrate or disperse
Adequate defense mechanisms against predators
Ability to cope with adverse conditions – migration, resistance to diseases, adapt to evtl. changes, etc.

10. Biotic Potential continued…
Intrinsic rate of increase (r) – rate at which a pop. could grow if it had UNLIMITED resources.
Not realistic!
No pop. can grow indefinitely due to factors that will slow growth eventually.

11. Limits to Pop. Growth continued…
Environmental Resistance- all the factors that can limit the growth and size of pops.
Abiotic Decreasing Factors:
Unfavorable light conditions – too little or too much
Unfavorable Temperatures
Unfavorable chemical environment - nutrients
Biotic Decreasing Factors:
Low reproductive rate
Specialized niche
Inability to migrate or disperse
Too many competitors
Inadequate defense mechanisms
Inability to cope with adverse conditions- not resistance to disease or unable to adapt to envtl. changes

12. Environmental Resistance continued…
There is a dynamic balance between biotic potential and environmental resistance.
Carrying capacity (K) - maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

15. Population Change and Carrying Capacity
Basic Concept:
Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)

16. Pop. change = (b + i) - (d + e)
Measuring Pop. Growth
Population growth depends upon
birth rates
death rates
immigration rates (into area)
emigration rates (exit area)
Pop. change = (b + i) - (d + e)

17. Population Growth Diagrams
Populations show two types of growth
Exponential
J-shaped curve
Growth is independent of population density
Logistic
S-shaped curve
Growth is not independent of population density

18. Exponential growth (J curve)
Fixed rate of increase, starting slowly and growing rapidly
Exponential curve is not realistic for long periods of time, due to carrying capacity of area.

19. Logistic Growth (S curve)
Because of environmental resistance, population growth decreases as density reaches carrying capacity
Graph of individuals vs. time yields a sigmoid or S-curved growth curve
Reproductive time lag causes population overshoot
Population will not be steady curve due to resources (prey) and predators

22. Density-Dependent Controls
Competition for resources
Predation
Parasitism
Disease

23. Density-Independent Controls
Natural disasters
Severe weather
Pollution
Pesticide spraying

24. 9-2: Reproductive Patterns and Survival
Goal of every species is to produce as many offspring as possible!
Each individual has a limited amount of energy to put towards life and reproduction
This leads to a trade-off of long life or high reproductive rate
Natural Selection has lead to two strategies for species: r - strategists and K - strategists

25. r - Strategists Spend most of their time in exponential growth
Maximize reproductive life
Minimum life K

26. r - Strategists Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental conditions
High population growth rate – (r)
Population size fluctuates wildly above and below carrying capacity – (K)
Generalist niche
Low ability to compete
Early successional species

27. K - Strategists Maintain population at carrying capacity (K)
Maximize lifespan K

28. K- Strategist Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental conditions
Lower population growth rate (r)
Population size fairly stable and usually close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
r and K strategists summary animation

29. Survivorship Curves
Late Loss (Type I) : K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality
Constant Loss (Type II): typically intermediate reproductive strategies with fairly constant mortality throughout all age classes
Early Loss (Type III) : r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age

30. Population Growth Self Quiz!
Late Loss
Constant Loss
Early Loss

31. 9-3: Effects of Genetic Variations in Pop. Size
Variations in genetic diversity can affect small, isolated populations. Most large pops. genetic diversity remains fairly constant.
Genetic variations that can affect small populations could include:
Founder effect – few individ. colonize a new area that’s geographically isolated from others in the population
Demographic Bottleneck effect – When a pop. is destroyed by natural disaster, and only a few individs. Survive; May lack genetic diversity to carry on and rebuild population.
Genetic drift – random changes in genes frequencies that could lead to unequal reproductive success; founder effect could cause genetic drift
Inbreeding – when individuals of small pops. mate and could increase likelihood of passing on defective genes to offspring and affect long term survival.

32. Genetic changes in a pop. due to the Bottleneck effect
Genetic Drift

33. 9-4: Human Impacts and Working with Nature
Nine major ways humans impact the environment to meet OUR needs and wants:
Fragmentation, degrading and destroying habitats
Simplifying/ homogenizing natural ecosystems (1 crop)
Using, wasting and destroying NPP that support all consumers.
Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
Elimination of some predators (sharks)
Deliberately or accidentally introducing new species (exotic)
Overharvesting potentially renewable resources (farmland, fish)
Interfering with the normal chemical cycling and energy flows in ecosystem (excessive CO2 emissions)
Increasingly more dependent on nonrenewable energy (fossil fuels)

34. Working with Nature: Principles of Sustainability
To maintain a balance between our altered environments and natural environments, we need to learn the important features of nature.
Nature sustains itself through:
(diagram on back cover of book!)
Uses of unlimited solar energy
Biodiversity
Nutrient recycling
Population Control

35. Ecological Principles for Sustainability (Message of the book and this class! )
We are part of, not apart from, the earth’s dynamic web of life.
Our lives, lifestyles, and economies are totally dependent on the sun and the earth.
We can never do merely one thing (first law of human ecology – Garret Hardin).
Everything is connected to everything else; we are all in it together.