Transcript CASE STUDY: CANE TOADS

Population Ecology
Key Concepts
Factors affecting population size
Species reproductive patterns
Species survivorship patterns
Conservation biology and
human impacts on ecosystems
CASE STUDY: CANE TOADS
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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.
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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.
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
Factors Governing Changes
in Population Size
• Four variable
– births, deaths,
immigration and
emigration
• Population Change =
(births +
immigration) –
(deaths + emigration)
OBJ 9.2
Age Structure Stages
• PREREPRODUCTIVE AGE
- Not mature enough to reproduce
• REPRODUCTIVE AGE
- Capable of reproducing
• POSTREPRODUCTIVE AGE
- too old to reproduce
LIMITING FACTOR
ABIOTIC
- temperature
- water
- climate/weather
- soils (mineral component)
BIOTIC
- competition: interspecific and intraspecific
- predation/parasitism
- amensalism
- mutualism
OBJ 9.3
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
OBJ 9.4
Exponential and Logistic Growth
LOGISTIC GROWTH
EXPONENTIAL GROWTH
- Rapid exp. growth followed by
steady dec. in pop. Growth
w/time until pop. Size levels off
-Population w/few resource
limitations; grows at a fixed rate
OBJ 9.5
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
Natural Population Curves
OBJ 9.7
Fig. 9-7 p. 168
• 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
The Role of Predation in
Controlling Population Size
 Top-down control
- lynx preying on hares
periodically reduce the hare
pop.
OBJ 9.8
 Bottom-up control
- the hare pop. may cause
changes in lynx pop.
Fig. 9-8 p. 168
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
OBJ 9.10
Reproductive Patterns and Survival
 r-selected species vs. K-selected species
Fig. 9-10 p. 170
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. 9-11 p. 171
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