Chapter 56- Ecology and Ecosystems
Define population and understand the characteristics of populations (density, dispersion patterns, survivorship curves)
population: group of individuals of a single species that occupy the same general area
density: the number of individuals of a species per unit area or volume
abiotic and biotic factors influence density, distribution and size of the population
survivorship curves: plot survivorships as the proportion of individuals from an initial population that are alive at each age
Type I: High survival rates during early and middle life, then a steep decline in old age (e.g., humans).
Type II: Constant death rate throughout life (e.g., some birds).Type III: High mortality early in life, but those that survive tend to live long (e.g., fish, many insects
dispersion patterns: way the individuals are spaced within the area
Clumped: Individuals are grouped together (e.g., herds, schools of fish).
Uniform: Individuals are evenly spaced (e.g., territorial animals).
Random: Individuals are randomly distributed (e.g., plants in a field).
Understand what population ecology studies:
changes in population size and factors regulating populations over time
Recognize and know how to calculate growth rates under the exponential growth model G= rN; know how to calculate r (per capita rate of increase) and G (J-shaped curve)
The exponential growth model represents unlimited growth, where a population grows at a constant rate, leading to a J-shaped curve.
Equation: G=rNG = rNG=rN
G = Growth rate of the population.
r = Per capita rate of increase (the rate at which individuals reproduce).
N = Current population size.
Calculating rrr (per capita rate of increase): This is the difference between the birth rate and death rate in a population. A high rrr value indicates rapid population growth.
J-shaped curve: When growth is unrestricted, the population size increases exponentially over time, but it is rarely sustained in real environments due to limiting factors (e.g., food, space).
Recognize and know how to calculate growth rates under the Logistic growth model G = rN(K-N)/K (S-shaped curve); understand carrying capacity (K) is the number of organisms in the population that the environment can support; the closer to K, the slower the growth rate (G) will become.
The logistic growth model considers environmental limitations such as resource availability, which leads to a carrying capacity (K), the maximum population size that the environment can support.
Equation: G= r*n
G = Growth rate of the population.
r = Per capita rate of increase.N = Current population size.
K = Carrying capacity (the maximum population size the environment can support).
S-shaped curve: The population initially grows exponentially, but as it approaches the carrying capacity KKK, the growth rate slows down and stabilizes.
Carrying capacity (K): The maximum number of individuals the environment can support based on available resources (e.g., food, space, water). As the population nears KKK, the growth rate (GGG) decreases.
Recognize J-shaped (exponential) and S-shaped (logistic) curves and interpret what they mean in regards to the environment
J-shaped curve (Exponential Growth): Represents unlimited growth, typically observed when a population is introduced to a new environment with abundant resources and no significant limitations.
Key features: Rapid, unchecked growth; usually unsustainable long-term.
S-shaped curve (Logistic Growth): Reflects the population’s growth that slows as it approaches the environment's carrying capacity. The population growth eventually stabilizes at the carrying capacity.
Key features: Growth starts exponentially, then levels off as resources become limiting.
Understand intraspecific competition; density-dependent factors; density-independent factors; “boom and bust” cycles
Intraspecific Competition: Competition within the same species for limited resources (e.g., food, mates, territory). This can regulate population size as resources become scarcer.
Density-dependent factors: Factors that increase in effect as population density increases. These factors are related to the number of individuals in the population and include:
Competition for food or mates.
Predation (more individuals can attract more predators).
Disease (diseases spread more easily in denser populations).
Density-independent factors: Factors that affect the population regardless of density and include environmental factors like:
Natural disasters (e.g., hurricanes, floods).
Temperature extremes.
Human activities (e.g., habitat destruction).
Some populations experience boom and bust cycles, where they grow rapidly (boom) when conditions are favorable (abundant resources, few predators), but then crash (bust) when resources become scarce or predators increase.
For example, rabbit populations may grow exponentially in favorable conditions, but then crash due to disease or predation (such as from foxes).