1. Population Ecology

2. Key Concepts Factors affecting population size
Species reproductive patterns
Species survivorship patterns
Conservation biology and human impacts on ecosystems

3. CASE STUDY: CANE TOADS
Cane toads (Bufo marinus, Bufonidae) naturally occur in the southern USA and the tropics of South America. Cane toads were deliberately introduced into Australia in an unsuccessful attempt to control pest beetles of sugar cane. About 3000 were first released near Cairns, northern Queensland, in July 1935.
There are no specific predators of cane toads in Australia.
The ability of cane toads to rapidly increase in number and expand into new areas and eat a large volume and variety of prey means they could displace many native species.
Toads prey on native animals especially insects and other invertebrates.
Toads out-compete native fauna such as small skinks and frogs for food.
Cane toads are poisonous at all stages of their life cycle.
Toads poison pets, humans, and native animals.

4. 9-1 Population Dynamics and Carrying Capacity
OBJ 9.1
Population dynamics
study of how populations change in size, density, and age distribution
populations respond to their environment
change according to distribution

5. Factors Governing Changes in Population Size
OBJ 9.2
Four variable
births, deaths, immigration and emigration
Population Change = (births + immigration) – (deaths + emigration)

6. Age Structure Stages PREREPRODUCTIVE AGE
- Not mature enough to reproduce
REPRODUCTIVE AGE
- Capable of reproducing
POSTREPRODUCTIVE AGE
- too old to reproduce

7. LIMITING FACTOR
OBJ 9.3
DEFINITION: anything that tends to make it more difficult for a species to live and grow, or reproduce in its environment
ABIOTIC - temperature
- water
- climate/weather
- soils (mineral component)
BIOTIC - competition:  interspecific and intraspecific - predation/parasitism - amensalism - mutualism

8. LIMITS TO POPULATION GROWTH: Resources & Competition
Biotic potential: capacity for growth
Intrinsic rate of increase (r): rate at which a population would grow if it had unlimited resources
Environmental resistance: all factors that act to limit the growth of a population
Carrying Capacity (K): maximum # of individuals of a given species that can be sustained indefinitely in a given space (area or volume)
Fig. 9-3 p. 166

9. Exponential and Logistic Growth
OBJ 9.4
LOGISTIC GROWTH
- Rapid exp. growth followed by steady dec. in pop. Growth w/time until pop. Size levels off
EXPONENTIAL GROWTH
Population w/few resource limitations; grows at a fixed rate

10. OBJ 9.5

11. Population Density Effects
OBJ 9.6
Density-independent controls
- floods, hurricanes, unseasonable weather, fire, habitat destruction, pesticide spraying, pollution
- EX: Severe freeze in spring can kill plant pop. regardless of density
Density-dependent controls
- competition for resources, predation, parasitism, infectious diseases
- EX: Bubonic plague swept through European cities in 14th century

12. Natural Population Curves
OBJ 9.7
Fig. 9-7 p. 168

13. STABLE
pop. Size fluctuates above or below its carrying capacity
Stable population size
EX: undisturbed tropical rain forests
IRRUPTIVE
pop. Growth occasionally explodes to a high peak then crashes to stable low level
EX: Algae, insects
CYCLIC
Fluctuations occur in cycles over a regular time period
EX: Lynx & snowshoe hare
IRREGULAR
No recurring pattern in changes of population size

14. The Role of Predation in Controlling Population Size
OBJ 9.8
Top-down control
- lynx preying on hares periodically reduce the hare pop.
Bottom-up control
- the hare pop. may cause changes in lynx pop.
Fig. 9-8 p. 168

15. How do Species Reproduce
ASEXUAL REPRODUCTION
all offspring are exact genetic copies of a single parent
Common in single celled species (bacteria)
Each cell divides to produce 2 identical cells
SEXUAL REPRODUCTION
Organisms produce offspring by combining sex cells or gametes from both parents
Produces offspring with combination of genetic traits from each parent
Provides greater genetic diversity in offspring
DISADVANTAGES
Males do not give birth
Increased chance of genetic errors and defects
Courtship & mating rituals consume time & energy and transmit diseases

16. Reproductive Patterns and Survival
OBJ 9.10
r-selected species vs. K-selected species
Fig p. 170

17. Survivorship Curves OBJ 9.11
Shows the % of members in a pop. Surviving at different ages
LATE LOSS
High survivorship to certain age; then high mortality
EX: elephants, rhinos, humans
CONSTANT LOSS
Fairly constant death rate at all ages
EX: songbirds
EARLY LOSS
Survivorship is low early in life
EX: annual plants, bony fish sp.
Fig p. 171

18. Human Impacts on Ecosystems
Habitat degradation and fragmentation
Ecosystem simplification
Genetic resistance
Predator elimination
Introduction of non-native species
Overharvesting renewable resources
Interference with ecological systems