1. 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
Natural selection favors a life history that maximizes lifetime reproductive success

2. Parental survival Kestrel Falcons:
The cost of larger broods to both male & female parents

3. 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

4. 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.”

5. Life strategies & survivorship curves25
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

6. Population growth change in population = births – deaths
Exponential model (ideal conditions)
dN = riN dt
growth increasing at constant rate
N = # of individuals
r = rate of growth
ri = intrinsic rate
t = time
d = rate of change
every pair has 4 offspring
every pair has 3 offspring
intrinsic rate = maximum rate of growth

7. Exponential growth rate
Characteristic of populations without limiting factors
introduced to a new environment or rebounding from a catastrophe
Whooping crane
coming back from near extinction
African elephant
protected from hunting
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.

8. 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

9. Introduced species Non-native species kudzu
transplanted populations grow exponentially in new area
out-compete native species
loss of natural controls
lack of predators, parasites, competitors
reduce diversity
examples
African honeybee
gypsy moth
zebra mussel
purple loosestrife
gypsy moth
kudzu

10. Zebra mussel reduces diversity
~2 months
ecological & economic damage
reduces diversity
loss of food & nesting sites for animals
economic damage

11. Purple loosestrife 1968 1978 reduces diversity
loss of food & nesting sites for animals

12. Logistic rate of growth
Can populations continue to grow exponentially?
Of course not!
no natural controls
K = carrying capacity
Decrease rate of growth as N reaches K
effect of natural controls
What happens as N approaches K?

13. Number of breeding male
Carrying capacity
Time (years)
1915
1925
1935
1945 10 8 6 4 2
Number of breeding male
fur seals (thousands)
Maximum population size that environment can support with no degradation of habitat
varies with changes in resources
500
400
300
200
100 20 10 30 50 40 60
Time (days)
Number of cladocerans
(per 200 ml)
What’s going on with the plankton?

14. Changes in Carrying Capacity
Population cycles
predator – prey interactions
At what population level is the carrying capacity? K K

15. Human population growth
Population of… China: 1.3 billion
India: 1.1 billion
Human population growth
adding 82 million/year
~ 200,000 per day!
Doubling times
250m  500m = y ()
500m  1b = y ()
1b  2b = 80y (1850–1930)
2b  4b = 75y (1930–1975)
20056 billion
Significant advances
in medicine through
science and technology
What factors have contributed to this exponential growth pattern?
Industrial Revolution
The population doubled to 1 billion within the next two centuries, doubled again to 2 billion between 1850 and 1930, and doubled still again by 1975 to more than 4 billion. The global population now numbers over 6 billion people and is increasing by about 73 million each year. The population grows by approximately 201,000 people each day, the equivalent of adding a city the size of Amarillo, Texas, or Madison, Wisconsin. Every week the population increases by the size of San Antonio, Milwaukee, or Indianapolis. It takes only four years for world population growth to add the equivalent of another United States. Population ecologists predict a population of 7.3–8.4 billion people on Earth by the year 2025.
Is the human population reaching carrying capacity?
Bubonic plague "Black Death"
1650500 million

16. Distribution of population growth
uneven distribution of population:
90% of births are in developing countries 11 10
high fertility
uneven distribution of resources:
wealthiest 20% consumes ~90% of resources increasing gap between rich & poor 9 8
There are choices as to which future path the world takes…
medium fertility 7
low fertility 6
World total
World population in billions
What is K for humans?
10-15 billion?
the effect of income & education 5 4
Developing countries 3 2 1
Developed countries
1900
1950
2000
2050
Time

17. individual at standard of living of population
Ecological Footprint
30.2
15.6
6.4
3.7
3.2
2.6
USA
Germany
Brazil
Indonesia
Nigeria
India
Amount of land required to support an
individual at standard of living of population 2 4 6 8 12 10 14 16 18 20 22 24 26 28 30 32 34
Acres
over-population or over-consumption?
uneven distribution:
wealthiest 20% of world:
86% consumption of resources
53% of CO2 emissions
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.

18. 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

19. Any Questions?

20. Measuring population density
How do we measure how many individuals in a population?
number of individuals in an area
mark & recapture methods
Difficult to count a moving target
sampling populations

21. Evolutionary adaptations
Coping with environmental variation
regulators
endotherms
homeostasis
(“warm-blooded”)
conformers
ectotherms
(“cold-blooded”)

22. Bright blue marble spinning in space
Ecology

23. Studying organisms in their environment
biosphere
ecosystem
community
population
organism