1. Why Population Ecology?
Scientific goal
understanding the factors that influence the size of populations
general principles
specific cases
Practical goal
management of populations
increase population size
endangered species
decrease population size
pests
maintain population size
fisheries management
maintain & maximize sustained yield

2. Life takes place in populations
group of individuals of same species in same area at same time
rely on same resources
interact
interbreed
Population Ecology: What factors affect a population?

3. Characterizing a Population
1937
1943
1951
1958
1961
1960
1965
1964
1966
1970
1956
Immigration
from Africa
~1900
Equator
Describing a population
population range
pattern of Dispersion
Density of population
range

4. adaptations to polar biome adaptations to rainforest biome
Population Range
Geographical limitations
abiotic & biotic factors
temperature, rainfall, food, predators, etc.
habitat
adaptations to polar biome
adaptations to rainforest biome

5. Population Dispersion
Spacing patterns within a population
Provides insight into the environmental associations & social interactions of individuals in population
clumped
Within a population’s geographic range, local densities may vary substantially. Variations in local density are among the most important characteristics that a population ecologist might study, since they provide insight into the environmental associations and social interactions of individuals in the population. Environmental differences—even at a local level—contribute to variation in population density; some habitat patches are simply more suitable for a species than are others. Social interactions between members of the population, which may maintain patterns of spacing between individuals, can also contribute to variation in population density.
random
uniform

6. Uniform
May result from direct interactions between individuals in the population
 territoriality
Clumped patterns
A uniform, or evenly spaced, pattern of dispersion may result from direct interactions between individuals in the population. For example, some plants secrete chemicals that inhibit the germination and growth of nearby individuals that could compete for resources. Animals often exhibit uniform dispersion as a result of antagonistic social interactions, such as territoriality —the defense of a bounded physical space against encroachment by other individuals. Uniform patterns are not as common in populations as clumped patterns.

7. Factors that affect Population Size
Abiotic factors
sunlight & temperature
precipitation / water
soil / nutrients
Biotic factors
other living organisms
prey (food)
competitors
predators, parasites, disease
Intrinsic factors
adaptations

8. Population Size Changes to population size
adding & removing individuals from a population
birth
death
immigration
Emigration
How can we measure a population?

9. Population growth rates
Factors affecting population growth rate
sex ratio
how many females vs. males?
generation time
at what age do females reproduce?
age structure
how females at reproductive age in cohort?

10. Demography Factors that affect growth & decline of populations
Why do teenage boys pay high car insurance rates?
Demography
Factors that affect growth & decline of populations
vital statistics & how they change over time
Life table
females
males
What adaptations have led to this difference in male vs. female mortality?

11. Survivorship curves Generalized strategies
What do these graphs tell about survival & strategy of a species?
Generalized strategies 25
1000
100
Human
(type I)
Hydra
(type II)
Oyster
(type III) 10 1 50
Percent of maximum life span 75
Survival per thousand
I. High death rate in post-reproductive years
II. Constant mortality rate throughout life span
A Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. In contrast, a Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
III. Very high early mortality but the few survivors then live long (stay reproductive)

12. Trade-offs: survival vs. reproduction
The cost of reproduction
increase reproduction may decrease survival
age at first reproduction
investment per offspring
number of reproductive cycles per lifetime
parents not equally invested
offspring mutations
Life History determined by
costs and benefits
of all adaptations
Natural selection favors a life history that maximizes lifetime reproductive success

13. Reproductive strategies
K-selected
late reproduction
few offspring
invest a lot in raising offspring
primates
coconut
r-selected
early reproduction
many offspring
little parental care
insects
many plants
K-selected
r-selected

14. Trade offs Number & size of offspring vs.
Survival of offspring or parent
r-selected
K-selected
“Of course, long before you mature, most of you will be eaten.”

15. Reproductive strategies & survivorship25
1000
100
Human
(type I)
Hydra
(type II)
Oyster
(type III) 10 1 50
Percent of maximum life span 75
Survival per thousand
K-selection
A Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. In contrast, a Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
r-selection

16. Growth Rate Models Exponential growth Logistic growth Rapid growth
No constraints
Logistic growth
Environmental constraints
Limited growth

17. Exponential growth rate
Characteristic of populations without limiting factors
Small population at start
introduced to a new environment or rebounding from a catastrophe, low competition, no predators
Ex: insects, annual plant, invasive species
The J–shaped curve of exponential growth is characteristic of some populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding. The graph illustrates the exponential population growth that occurred in the population of elephants in Kruger National Park, South Africa, after they were protected from hunting. After approximately 60 years of exponential growth, the large number of elephants had caused enough damage to the park vegetation that a collapse in the elephant food supply was likely, leading to an end to population growth through starvation. To protect other species and the park ecosystem before that happened, park managers began limiting the elephant population by using birth control and exporting elephants to other countries.
“Boom and Bust”
Does this growth last?

18. Logistic rate of growth
Growth rate slows as K is reached.
no natural controls
K = carrying capacity
Decrease rate of growth as N reaches K
Causes: Energy limitations, water, shelter, predators, parasites
effect of natural controls

19. Carrying capacity Maximum population size that environment can support
Varies over time and space

20. Negative feedback response to regulate populations
Population cycles
predator – prey interactions
Hard to define K
Negative feedback response to regulate populations

21. Regulation of Population Size
marking territory = competition
Limiting factors
density dependent
competition: food, mates, nesting sites
predators, parasites, pathogens
density independent
abiotic factors
sunlight (energy)
temperature
rainfall
swarming locusts
competition for nesting sites

22. Population growth math
change in population = births – deaths
N is the change in population size
t is the time interval
B is the number of births
D is the number of deaths

23. Need to know: Number of organisms = N Rate of growth = r
r = birth rate – death rate
Birth rate (b) = B (#births)/N
Death rate (d) = D (#deaths)/N
r is always a decimal
When r = 0, no growth is occurring!! ZPG
Births and deaths still occur but in equal #’s

24. Exponential Population Growth
Rewritten with “r” when max growth rate is needed.
If rate is faster then growth is faster N t  rN

25. Logistic Population Growth
Carrying Capacity must be added…
Population is greatest at approx. ½ the carrying capacity
K = carrying capacity; fixed number

26. Invasive Species Non-native species kudzu Exponential growth
out-compete native species
loss of natural controls
lack of predators, parasites, competitors
reduce diversity
examples
Cane toads
Zebra mussel
Purple loosestrife
kudzu

27. Age structure Relative number of individuals of each age
What do these data imply about population growth in these countries?

28. Distribution of population growth
uneven distribution of population:
90% of births are in developing countries 11 10
high fertility 9
uneven distribution of resources:
wealthiest 20% consumes ~90% of resources increasing gap between rich & poor 8
medium fertility 7
low fertility 6
World total
World population in billions
What is K for humans?
10-15 billion? 5 4
Developing countries 3 2 1
Developed countries
1900
1950
2000
2050
Time

29. Ecological Footprint deficit surplus
A more comprehensive approach to estimating the carrying capacity of Earth is to recognize that humans have multiple constraints: We need food, water, fuel, building materials, and other requisites, such as clothing and transportation. The ecological footprint concept summarizes the aggregate land and water area appropriated by each nation to produce all the resources it consumes and to absorb all the waste it generates. Six types of ecologically productive areas are distinguished in calculating the ecological footprint: arable land (land suitable for crops), pasture, forest, ocean, built–up land, and fossil energy land. (Fossil energy land is calculated on the basis of the land required for vegetation to absorb the CO2 produced by burning fossil fuels.) All measures are converted to land area as hectares (ha) per person (1 ha = 2.47 acres). Adding up all the ecologically productive land on the planet yields about 2 ha per person. Reserving some land for parks and conservation means reducing this allotment to 1.7 ha per person—the benchmark for comparing actual ecological footprints.
The graph is the ecological footprints for 13 countries and for the whole world as of We can draw two key conclusions from the graph. First, countries vary greatly in their individual footprint size and in their available ecological capacity (the actual resource base of each country). The United States has an ecological footprint of 8.4 ha per person but has only 6.2 ha per person of available ecological capacity. In other words, the U.S. population is already above carrying capacity. By contrast, New Zealand has a larger ecological footprint of 9.8 ha per person but an available capacity of 14.3 ha per person, so it is below its carrying capacity.
The second conclusion is that, in general, the world was already in ecological deficit when the study was conducted. The overall analysis suggests that the world is now at or slightly above its carrying capacity.
Based on land & water area used to produce all resources each country consumes & to absorb all wastes it generates