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Population Ecology -->

Concept Review

When trying to get a grasp on the biosphere and what causes it to change we need to consider several things all at once. We have already covered and but why do things matter? Why do we need to know about ? Simply put, this is the bases for



energy pyramids

Population Ecology


Population Ecology is the study of how different species and how theyWe put the things the affect population growth into 2 groups:

interact with their enviroment

continue their species



It's all about babies! (kinda)

Populations are always trying to undergo but many factors will limit populations, we call these . These limiting factors create an actual population growth known as Very simply though how much of a population is determined by the number of births, deaths and movement of the populations.

  • Birth and Emigration (moving to) = increases in population
  • Death and Immigration(moving away) = decreases in population
can be determined by a number of other factors like the where an animal lives, births and deaths or their

Exponential Growth

Population Density

Logistical Growth

relationships with other populations

limiting factors

We're all in this together

Populations of animals live together because it takes all of them to maintain an ecosystem. Through a series of relationships animals can help and sometimes hurt one another. We can think of ecosystems like cities where all the living organisms fill a job, we call this job a These niches break down into 3 major types of relationships that animals have with each other, we generally refer to this idea of organisms having "realtionships" as symbiosis.





When we combine all the ideas of population growth or decline and what contributes to it we get the idea of There are several examples of how carrying capacity can change based on regions or in extreme events. Extinction is when all members of a species are removed from a specific region or the whole world. When extinction occurs in specific areas splitting up 2 populations of a species they might undergo , this is where 1 species turns into 2 or more subspecies or entirely different species.

Put it all together

Carrying Capacity



Commensalism is where 1 organism benefits but nothing really happened to the other. Barnacles are small animals that need to be able to move through the ocean to collect food. They don’t move well on their own so they will attach themselves to Gray Whales as an easy way to fix this problem. This doesn’t hurt the whales in any way but it also doesn't help the whales.

If you have ever seen a bird pull the fur off a deer or a fish climb into a shark's mouth you have seen mutualism. Mutualism is where both organisms benefit. In the case of the bird and the deer, the deer gets rid of hot fur and the bird gets comfy nesting material. With the shark and the fish, the shark gets clean teeth and the fish gets a snack.


Limiting Factor

Limiting factors are the things that make populations smaller or make the growth slower and they are broken into 2 big categories. Independent Limiting Factors: Something that affects the population size that has an impact equal to the size of the population. For example things like diseases, competition for food or predators. Dependent Limiting Factors: Something that affects the population that has nothing to do with population. For example an asteroid.




The measure of the amount of different species in an ecosystemScientist measure biodiversity with numerical values but for our purposes we will think in the terms of high or low biodiversity. The highest biodiversity would be a rainforest, a 10-square-kilometer (four-square-mile) patch can contain as many as 1,500 flowering plants, 750 species of trees, 400 species of birds and 150 species of butterflies. A low biodiversity would be for example this classroom, with only a singular species. (Maybe a few more if you count the spiders we can’t see)

Carrying Capacity is the amount of a species that can successfully live in an ecosystem. The carrying capacity is based around the amount of resources, both biotic and abiotic, available to a species. These factors include shelter, food, breeding space, safety from predators or disease.We like to think that carrying capacity is affected by predators but in reality the amount of prey is what controls the number of predators. A rabbit is a resource for a wolf, that is why as we increase the rabbit population the wolf population will also increase.

Carrying Capacity

Changes in the ecosystem many create a number of carrying capacity graphs: Most common of them are cyclical but occasionally we get other types. The Damped Oscillation may occur when there is a random change but that change eventually evens out. For example, an extra wet winter may create a greener spring, but this is not an ongoing benefit.This could be an increase due to immigration, the population will suddenly increase but eventually will become stable. A Crash on the other hand is the opposite problem where a large member of the population dies off, by disease or disaster. In the graph we see the population trying to recover, though if it doesn’t it may go extinct. Finally Chaotic, this can be any combination of favoriable or unfavorable events, there is no common root cause

Biotic refers to things that are alive.

  • Plants
  • Animals
  • Food
  • Predators
  • Ability to have offspring
  • Disease


Logistical Growth

Logistical growth is the growth of a population in relation to their resources. For example: In an ecosystem where a rabbit only eats 1 type of grass. The ammount of rabbits depends on the amount of food. The food is the limiting factor.We generally put these resources into 2 buckets

abiotic and biotic

Abiotic refers to things that are not alive.

  • Water
  • Rocks
  • Temperature
  • Weather
  • Natural Disasters


Exponential Growth

The continuously increasing growth. What this means is that with every generation we could see the population double in size. While this would be great if our money was always doubling, organisms cannot grow this much.

Energy Pyramid

Energy pyramids combine the ideas of trophic levels and the “10% rule” of energy loss. Trophic Level: A way to think of the “space” an organism lives in the ecosystem. What might it eat and what eats it. 10% rule: The idea that only 10% of the energy from something a heterotroph (consumer) gets converted into mass and the rest is lost to heat, digestion, etc.


A geographic area is distinct in geography, climate and living organismsIt is important to remember that ecosystems do not have strict edges but can be rather fuzzy depending on what we are studying. If I care about studying Canadian Geese my ecosystem is going to stretch all the way from Canada to Mexico. On the other hand if I want to study the effects of taking Environmental Science with Ms Garcia and Ms Coney on 9th graders in Golden Colorado, I only have to look at 2 classrooms.


A niche essentially the job an organism fills in an ecosystem. It is a combination of their trophic level (what it eats and what eats it) but also how the organism spends its day. For Example: Pinion Jays have a very specific niche of not only being a secondary consumer but they are responsible for a large portion of the Pinion Pine trees. Pinion Jays will hide seeds on the ground to save for winter but whatever seeds are not used will sprout into trees. This particular niche is only occupied by 1 other animal in the first and that is squirrels. On the other hand the Pinion Pines niche of providing shade and animals places to live could be filled by a lot of different trees.

A major examples of speciation are the Florida Panther vs the Mountain Lion. Mountain Lions and Florida Panthers share common ancestors, in fact they were the same type of animal. However, western expansion and large distance split the population, now creating 2 different subspecies. Speciation occurs when 2 populations are split apart and no longer intermingal. This is done by people, geography or climate change.



Parasitism is when one organism benefits and the other is harmed. Unfortunately, many of these examples are pretty gross. Tapeworms are a type of worm that can enter an animal by accident when it eats tapeworm eggs. Once the tape worm is inside the animal it will grow and reproduce inside the animal's stomach. As it grows it will eat the food in the stomach slowly starving the animal.

Population density describes the amount of a species that lives in a specific size, or area of land. For example, I may want to study Mountain Lions. It would be important for me to think about where there would be a lot or a little. If I set my area to the whole United States, I could think incorrectly that Mountain Lions are spread out everywhere, but I know that I am more likely to see one in Colorado than in Kansas. This means I should set my area to Colorado, but I could set my area even smaller than that because I am more likely to see one in George Town than I am on the plains in Limon.

Population Density

More simply put I can look at just the population of Ouchtown and the density would be really low, because only you are there.