Note
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Unit 8 Topic 1-3 (AP BIO)
Ecology is the study of the interactions between organisms and the environment
An organism's environment includes a large range of biotic and abiotic factors.
Abiotic factors are nonliving
components, such as
temperature, water, light,
Nutrients, and soil types.
Biotic factors are living (or once
living) components which
include all of the other organisms
(plants, animals, fungi, bacteria,
etc.) present in the environment.
Ecology can be broken down into different levels of organization:
Organism: a living thing, which includes plants, animals, fungus, and bacteria and other microorganisms.
Population: a group of individuals of the same species living together in the same geographic area.
Community: groups of populations of different species that inhabit a particular area.
Ecosystem: all of the abiotic factors and the entire community of species that exist in a certain area.
Biosphere: the entire planet and all of the ecosystems found on Earth.
Habitat: the place or part of an ecosystem that an organism occupies
Ex: the habitat of a tropical tree lizard includes the forests in which they are found and the specific environments within those forests that they occupy.
Niche: the role of an organism within its ecosystem, which includes how an organisms interacts with the biotic and abiotic factors in its environment.
Ex: The niche of a tropical tree lizard includes the temperature ranges it tolerates, the size of branches it perches on, the time of day it is active, and the sizes and kinds of insects it eats.
The size of a population (N) is the number of individuals that live in the population.
Population size is affected by several factors:
Births and immigration (movement of new individuals into a population) cause population sizes to increase
Deaths and emigration (movement of individuals out of a population) cause population sizes to decrease
Population Growth Formula (ignoring immigration and emigration):
dN/dt = change in pop. size over change in time (growth rate)
B = birth rate
D = death rate
The growth rate of a population can also be determined by finding the slope of the line on a graph showing population size vs. time.
Populations that experience reproduction without constraints experience exponential growth.
Without constraints = abundant space and resources and lack of competition, predation, and disease.
Exponential growth leads to a population increasing in size at a faster and faster rate, creating a J-shaped growth curve over time.
Exponential Growth Formula:
rmax = maximum per capita growth rate of population (# of offspring per individual per unit of time)
The per unit of time is usually per year.
N = population size
In exponential growth, the per capita growth rate remains constant, no matter the population size.
Exponential growth is not sustainable. There is ultimately a limit to the number of individuals that can occupy a habitat.
Carrying capacity (K) is the maximum population size that a particular environment can sustain.
Carrying capacity can vary and changes depending on environmental conditions and the availability of resources.
Energy, shelter, refuge from predators, nutrient availability, water, and space can all be factors that affect carrying capacity.
Logistic growth is seen in populations affected by carrying capacity.
In logistic growth, the per capita growth rate gets smaller and smaller (eventually becoming 0) as the size of the population (N) approaches the carrying capacity (K).
This produces an S-shaped curve over time.
The population size will level off, or fluctuate, at the carrying capacity.
Logistic Growth Formula
rmax = maximum per capita growth rate of population
N = population size
K = carrying capacity
Factors that limit population growth are called limiting factors, which can be density-dependent or density-independent.
Density-dependent limiting factors are ones that affect the growth rate of a population differently depending on how dense a population is.
The greater the population density = the greater the ability of the limiting resource to reduce population growth.
Ex: Competition for resources (food, shelter, space, light, etc.), predation, and disease are all factors that affect higher density populations more than lower density populations.
Density-independent limiting factors are ones that affect the growth rate of a population independently of how dense a population is.
The limiting factor has the same ability to reduce population growth in both low and high densities.
Ex: natural disasters (such as floods, wildfires, hurricanes, etc.) occur at frequencies and severities that are independent of population densities.
Interspecific interactions refer to relationships between different species.
These interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or neutral (0)
Negative (-) interaction: the growth and size of a population is less than what it would be in the absence of the interaction.
Positive (+) interaction: the growth and size of a population is greater than what it would be in the absence of the interaction.
Neutral (0) interaction: the growth and size of the population is the same as what it would be in the absence of that interaction.
Types of Interspecific Interactions: Competition (-/-), Predation & Herbivory (+/-), Parasitism (+/-), Commensalism (+/0), and Mutualism (+/+).
Interspecific competition is an example of a -/- interaction that occurs when individuals of different species compete for a resources that limits the survival and reproduction of each species.
The population size/growth of the two species is lower when living together than living separately.
Competition occurs between species when they have overlapping niches.
The competitive exclusion principle states that two species competing for the exact same resources cannot permanently coexist in the same place.
Similar species can coexist in a community if they differentiate their niches, which is called resource partitioning.
Ex: Seven species of Anolis lizards live in close proximity, and all feed on small insects. However, competition for food is reduced because each lizard has a different preferred perch.
The consumption of another organism through predation (animals eating animals) or herbivory (animals eating plants) is an example of a +/- interaction, where one species benefits, and the other is harmed or killed.
Predator-prey relationships: the population sizes of predators and their prey are closely tied to one another.
As the population of prey increases, the population of predators increases shortly after. This leads to increases in predation and a corresponding decrease in the prey population. The predator population declines shorty after. The cycle then continues.
Symbiosis is a general term for interspecific interactions in which two species live together in a long-term, intimate association, with a variety of positive or negative effects on the participants.
Types of symbiotic relationships:
Parasitism = (+/-)
Commensalism = (+/0)
Mutualism = (+/+)'
In parasitism, two species have a close, lasting interaction that is beneficial to one, the parasite, and harmful to the other, the host (+/- interaction).
Ex: heartworms and ticks in dogs are both examples of parasites that benefit from the host (dog), at the cost of the host being harmed.
In commensalism, two species have a long-term interaction that is beneficial to one and has no positive or negative effect on the other (+/0 interaction).
Ex: Cattle egrets feed on insects flushed out of the grass by grazing bison. The bison are unaffected by the presence of the egrets.
In mutualism, two species have a long-term interaction that is beneficial to both of them (+/+ interaction).
Ex: Mycorrhizae (root fungi) form a mutualistic relationship with many types of pants. The plant can photosynthesize and provides the fungus with fixed carbon in the form of sugars and other organic molecules. The fungus has a network of threadlike structures called hyphae, which allow it to capture water and nutrients from the soil and provide them to the plant.