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Title: Population and Community Ecology
Description: These notes discuss what ecology is, and how different animals and species interact with one another. The different interactions, such as competition and parasitism are discussed, as well as human population ecology. These notes were taken for an introductory college biology course.
Description: These notes discuss what ecology is, and how different animals and species interact with one another. The different interactions, such as competition and parasitism are discussed, as well as human population ecology. These notes were taken for an introductory college biology course.
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Population and Community Ecology
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Ecology is the study of the interactions between organisms and their environments
A population is a group of individuals of the same species
Communities are individuals of different species interacting with one another
Population ecology
o Must be interbreeding
o How do individuals within a population change over time in terms of growth
rates? In terms of distributions? In terms of genetic composition?
Growth rate is the change in number of individuals in a population over time
o If number of births > than number of deaths, population grows, and vice versa
o There are two models of population growth
▪ Exponential growth is unchecked growth
▪ Logistic growth is when population grows quickly at first, but then slows as
the population size reaches the carrying capacity (k)
• K is the max number of individuals an environment can hold
o Factors that limit growth
▪ Predator population
▪ Amount of resources, such as food and water
▪ Spread of disease, especially as the population becomes more dense
▪ Natural disasters
o Populations can oscillate between large and small, and this is a natural
fluctuation
Human population growth has greatly increased in the past two hundred years, from 1
billion in 1850 to more than 7 billion in our present day
o Population structure is an important demographic factor in predicting growth
▪ Afghanistan is rapid, United States is slow, and Italy is no growth
• Using the distribution of population via age to show growth, and the
more young people there are, the faster the country is growing
▪ The diagrams can illuminate demographic/social conditions and help us
plan for the future
• Invest in more schools? Need more agriculture production? Etc
o How many humans can the earth support? ~ 10 billion
▪ Our carrying capacity could be potentially limited by food, space,
nonrenewable resources, or buildup of waste
▪ Unlike other organisms, we can regulate population growth through social
changes
• Expand into new habitats
• Increase the agricultural productivity of the land
• Finding ways to live at higher densities
o Population growth is higher in developing countries versus developed countries
Community ecology
o Populations of different species interact with one another to form communities
o A biological community is an assemblage of populations of various species living
close enough for potential interaction
o Ecologists call relationships between species as interspecific interactions
Population and Community Ecology
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Competition, predation, symbiosis, facilitation
Can affect the survival and reproduction of each species, and the effects
can be positive (+), negative (-), or have no effect
Community interactions
• Competition (-/-)
• Occurs when species compete for a resource in short supply
• Strong competition can lead to competitive exclusion, local
elimination of a competing species
• Predation (+/-)
• One species, the predator, kills and eat the other, the prey
• Some feeding adaptations of predators are jaws with sharp
teeth, stingers, and poison
• Exerts strong selective pressure on prey
• Behavioral defenses include hiding, fleeing, forming herds
or schools, self defense, and alarm calls
• Also many morphological and physiological defenses
• Cryptic coloration, or camouflage, makes prey difficult to
spot
• Coloration can be a warning that prey are dangerous
• Sometimes nonpoisonous species mimic the
coloration and patterns of other poisonous ones
• Symbiosis is a relationship between two or more species that involves
very direct and intimate contact with one another
• Parasitism (+/-)
• One species, the parasite, derives nourishment from the
other organism, the host
• Many parasites have a complex life cycle that involve a
number of hosts
• Some parasites change the behavior of the host in a way
that increases the parasites' fitness
• Mutualism (+/+)
• Both species involved are benefited from the interaction
• Ants and acacia trees
• Ants feed on the trees and lay eggs in the
branches, and the ants protect the tree from
destructive animals and clear out plant
competitors
• Commensalism (+/0)
• One species is benefitted and the other is neither harmed
nor helped by the interaction
• Tend to be more rare in nature
• Egrets ride on top of water buffalo to get a better
view of food and predators, and the water buffalo
are not really affected
Population and Community Ecology
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Facilitation (+/+) or (0/+)
• One species has a positive effect on another species without
direct and intimate contact
• Black rush is a plant that makes the soil more fertile for
other plant species
Title: Population and Community Ecology
Description: These notes discuss what ecology is, and how different animals and species interact with one another. The different interactions, such as competition and parasitism are discussed, as well as human population ecology. These notes were taken for an introductory college biology course.
Description: These notes discuss what ecology is, and how different animals and species interact with one another. The different interactions, such as competition and parasitism are discussed, as well as human population ecology. These notes were taken for an introductory college biology course.