1. Population Dynamics

2. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

3. Characteristics of a Population
Population - individuals 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 Size Natality Mortality
Number of individuals added through reproduction
Crude Birth Rate - Births per 1000
CBR= (Births/Population)*1000
Total Fertility Rate – Average number of children born alive per woman in her lifetime
Mortality
Number of individuals removed through death
Crude Death Rate Deaths per 1000

5. 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

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

7. Population Dispersion
Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced
tips/2002/clover611.htm
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

8. Population Histogram
A population histogram shows the age structure of a population and is usually shown graphically
The population is usually divided up into prereproductives, reproductives and postreproductives
The age structure of a population dictates whether is will grow, shrink, or stay the same size

9. Population Histograms
Positive Growth Zero Growth Negative Growth
(ZPG)
Pyramid Shape Vertical Edges Inverted Pyramid

10. Population Dynamics Outline
Characteristics of a Population
Population Dynamics
Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

11. Biotic Potential
Ability of populations of a given species to increase in size
Abiotic Contributing Factors:
Favorable light
Favorable Temperatures
Favorable chemical environment - nutrients
Biotic Contributing Factors:
Reproductive rate
Generalized niche
Ability to migrate or disperse
Adequate defense mechanisms
Ability to cope with adverse conditions

12. Environmental Resistance
Ability of populations of a given species to decrease in size (limiting factors)
Abiotic Contributing Factors:
Unfavorable light
Unfavorable Temperatures
Unfavorable chemical environment - nutrients
Biotic Contributing Factors:
Low reproductive rate
Specialized niche
Inability to migrate or disperse
Inadequate defense mechanisms
Inability to cope with adverse conditions

13. Environmental Resistance
Biotic Potential
factors allow a population to increase under ideal conditions, potentially leading to exponential growth
Environmental Resistance
affect the young more than the elderly in a population, thereby affecting survival to reproductive age

15. Population Growth Population growth depends upon birth rates
death rates
immigration rates (into area)
emigration rates (exit area)

16. Population Growth 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

17. Exponential Growth
As early as Darwin, scientists have realized that populations have the ability to grow exponentially
All populations have this ability, although not all populations realized this type of growth
Darwin pondered the question of exponential growth. He knew that all species had the potential to grow exponentially
He used elephants as an example because elephants are one of the slowest breeders on the planet

18. Exponential Growth 19,000,000 elephants!!!
One female will produce 6 young over her 100 year life span. In a population, this amounts to a growth rate of 2%
Darwin wondered, how many elephants could result from one male and one female in 750 years?
19,000,000 elephants!!!

19. Exponential Growth Graph

20. Population Dynamics 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)
There is a dynamic balance between biotic potential and environmental resistance

21. Carrying Capacity (K)
Exponential curve is not realistic due to carrying capacity of area
Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

23. Logistic Growth
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

26. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts

27. Reproductive Strategies
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

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

29. 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 in size
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

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

31. 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

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

34. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Human Impacts

35. Human Impacts Fragmentation and degrading habitat
Simplifying natural ecosystems
Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
Elimination of some predators

36. Human Impacts Deliberately or accidentally introducing new species
Overharvesting potentially renewable resources
Interfering with the normal chemical cycling and energy flows in ecosystem

37. Habitat Fragmentation
Process by which human activity breaks natural ecosystems into smaller and smaller pieces of land
Greatest impact on populations of species that require large areas of continuous habitat
Also called habitat islands

39. Habitat fragmentation in northern Alberta
Habitat fragmentation in northern Alberta

40. Principles of Sustainability
Solutions
Principles of Sustainability
Lessons for Us
How Nature Works
Runs on renewable solar energy.
Recycles nutrients and wastes. There is little waste in nature.
Uses biodiversity to maintain itself and adapt to new environmental conditions.
Controls a species population size and resource use by interactions with its environment and other species.
Rely mostly on renewable solar energy.
Prevent and reduce pollution and recycle and reuse resources.
Preserve biodiversity by protecting ecosystem services and preventing premature extinction
of species.
Reduce births and wasteful resource use to prevent environmental overload and depletion and
degradation of resources.

41. Four Principles for Sustainablility
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.