Populations BY: matt bellia

Nature is Made Up Of 5 Levels of Life and Living Things

  • Individual: This represents a single organism - Scientists observe how natural selection works at this level, also they see how organisms react to certain things.
  • Population: A population is all the organisms of a species living in a certain area at a given time - Scientists study factors that cause the number of individuals to increase or decrease and evolution occurs at this level as well.
  • Community: A community is all of the populations of organisms in a given area - The main thing scientists study here are the interactions between different species (i.e. Deer and Coyotes).
  • Ecosystem: This contains all of the biotic and abiotic elements in a given location - Scientists study the flow of energy and nutrients between living and non-living things at this level.
  • Biosphere: All of earths ecosystems are contained in this level - At this level Scientists observe the movement of air, water, and heat around the world / the following video shows how CO2 travels around the biosphere

Friedland, Andrew, and Rick Relyea. "Chapter 6." Environmental science for AP. 2nd ed. W.H. Freeman, 2015. 192. Print.

Part of a population

Population Vocabulary

  • Population size: Total number of individuals in a given area at a certain time - The population size lets us know how well a population is doing, if the number is high and stays high then the species is thriving wherever it is, if the number low this gives scientists the clue that the population is nearing extinction and should be protected.
  • Population density: How many individuals of a species are alive per unit area - Shows us where a species might strip its food supply because there are to many organisms living there and shows where certain species are rarer at and laws can be enacted to protect organisms in certain areas more then other places.
  • Population distribution: Description of how individuals are spaced out in relation to other members of the same species - Scientists use this to figure out behavior among certain groups and if they are territorial, also lets us know where the favored nesting spots are at for certain species.
  • Population sex ratio and age structure: The sex ratio is just simply the ratio of male to female members of a population, and the age structure is how many individuals fit into certain age categories. These both help to understand how fast populations will grow, if there are a lot more females then males then the population will grow faster then one with less females. If a population is filled with to old or to young that means that the amount of offspring produced that year won't be where it should be. A population with a good mixture of both will be the most healthy.
Example of Sex Ratio - one male per handful of females. this means the males will have less trouble trying to find another mate to pass their offspring on with.

Density-Dependent and Density-Independent Factors

  • Dependent: A factor that influences populations survival in a way that depends on the population size. The biggest example is food availability, if a large population moves into an area, there is less food per individual then a population with a few, the smaller population will survive much better then a larger one.
  • Independent: This factor influences populations survival in a way that doesn't take into account the population size, it would have the same effect in a population of 100 and 1,000,000. For example, weather and climate would be independent factors.
Example of Independent factor, weather affects species in many important ways regardless of the size of their populations.

Carrying Capacity and Limiting Recourses

  • Both of these terms are related very closely. Carrying Capacity is the limit of organisms a certain area can shelter and provide land to live for. If a certain area is lacking certain important things it won't be able to host a lot of living things, but if the land is large and valuable resources are abundant then animals will be able to grow their population very high. Most carrying capacities are affected by limiting resources (things life are dependent on) such as water and food sources. And if they lack limiting resources the population won't be able to exceed the carrying capacity.

Friedland, Andrew, and Rick Relyea. "Chapter 6." Environmental Science for AP. 2nd ed. W.H. Freeman, 2015. 193-194. Print.

Limiting resource

Growth Models, Reproductive Strategies, Survivorship Curves, and Metapopulations

  • Intrinsic Growth Rate: This is the maximum potential growth rate, so under ideal conditions and given unlimited resources each population has a growth rate which they could never really achieve out in the wild, this growth rate is called the Intrinsic Growth rate.
  • Exponential Growth Rate: When the growth rate becomes even more rapid in proportion to the size of the population, so when the population grows larger, the reproduction gets ever more faster, making a cycle.
Example of a graph for Exponential Growth (math.tutorvista.com)
  • Logistic Growth Rate: This is when the population growth decreases when it approaches the environments carrying capacity, it will produce fast at first but slows down once the carrying capacity is either reached or closing in
Example of Logistic Growth Rate (bio1510.biology.gatech.edu)

Overshoots, Die-offs, and Carrying Capacity

  • How they relate: An overshoot is when a certain population goes over the environments carrying capacity and is over what their environment can support. Then after the population over shoots it will experience a die off. Die-offs happen when a number of individuals die due to the population being over the natural carrying capacity, because there isn't enough of a certain resource. Once it reaches a healthy number that agrees with the carrying capacity and there are enough resources to go around they will hover around that number unless a force acts upon them.

Predator and Prey

  • How they relate: The predator plays a large roll on the prey population and same the other way around. Once the Prey reaches a peak in their population the predator will as well a couple years after because now their is a larger food source available to them, but after the predator population rises the prey starts to shrink back because of the increase number of predators and also there is less food now because of their numbers. So the prey shrinks back down, and due to this the predators will also shrink back down due to less food as well. It goes on like this forever, a constant up and down between each of their populations.
Graph showing the relations of predator and prey (mojavedesert-biomeproject.wikispaces.com)
  • K-Selected Species: These designated species are generally larger animals that can't reproduce till later in their life, Once they do reproduce they have a few large offspring and provide a lot of parental care to them. This all adds up to slow population growth rate and the population tends to hang around the carrying capacity. For example elephants, cows, and deer, are all K-selected species.
  • R-Selected species: These animals experience overshoots and die-offs quite frequently due to there high reproduction rate, they are mature at very young ages and have short life spans. They also produce many offspring and don't provide much parental care to them. For example small insects like mosquitoes are R-selected, as well as rats, weeds, and cockroaches.
Difference between K-selected and R-selected species graphs (socratic.org)
  • Corridors and Meta-Populations: Corridors are strips of natural land that connect different groups of the same species in an area. Meaning that if there are 4 hills and there are groups on each hill, there would be a path that they could travel to go socialize and reproduce with the other groups. This is important because it keeps the genetic variation high within these separated groups. If these didn't exist each small group would be lacking genetic variation and they would all be similar and susceptible to things like diseases that could wipe them out. So this is beneficial for their overall survival. A Meta-population is what all of the different groups of animals in an area all called.

Friedland, Andrew, and Rick Relyea. "Chapter 6." Environmental science for AP. 2nd ed. W.H. Freeman, 2015. 197-200. Print.

Interactions Between Animals and Species

  • Competitive Exclusion Principle: 2 species competing for the same limiting resource cannot coexist
  • This completion leads to Resource Partitioning as both species try to find the easiest way to get the resource that they need. For example, Resource Partitioning is if there are 2 different species trying to eat a type of berry, the 1st species eats red and blue berries, and the 2nd species eats blue and orange berries. These species over time will then eliminate the overlap, so the 1st species will eventually primarily feed on their red berries, and the 2nd species will stick to their orange berries. This eliminated the completion involved in eating the blue berries and makes their lives easier

4 Types of Predators

  • True Predators: These animals will kill and consume other animals (Lions)
  • Herbivores: These animals will consume plants / producer (Rabbit)
  • Parasites: They live on or inside other animals (Tape Worm)
  • Parasitoids: These animals lay their eggs in other animals (Types of Wasps)
An example of a true predator

Why is Predation Beneficial? - Predators regulate the population of their prey. Without coyotes for example, the deer population would rise much more then it already is and then they would overgraze and use up their resources, so the coyotes ultimately help the deer because without them the population would rise to much and the food would be used up and it would take a long time for it to grow back fully.

Defense Mechanisms of Prey

  • Hiding / Reduced Movement: This attracts less attention and makes it harder for predators to detect the prey.
  • Camouflage: This is a certain pattern on prey that blends in with their common surroundings and makes it hard for them to be seen.
  • Spines: Many animals such as the porcupine, stingray, and pufferfish have spines that deter predators to attack them, plants also have spikes and thorns to keep animals away as well.
  • Chemical: This includes types of poisons and chemicals that are distasteful for predators.
  • Mimicking: Most toxic animals are brightly colored to warn others that they are in fact toxic, but some animals have developed those same colors, however these animals are not toxic, but trick animals into thinking they are by there "fake" appearance that resembles the actual toxic animals.
A Porcupine that has spikes to protect itself from predators

Symbiotic Relationships

  • Mutualism: Both of the species in this relationship benefit from each other in certain ways by helping the other. For example, Oxpeckers and Rhinos, the Oxpecker eats the bugs and parasites off of the Rhinos back and gets a readily easy and available food source to get to, and the Rhino gets the bugs and parasites off of it to stay healthier.
  • Commensalism: Where one species benefits and the other species isn't effected at all. For example, Clownfish and Anemones, The clown fish get a home which protects it from other fish, and the Anemone isn't effected or bothered.
  • Parasitism: where one species lives on or in another species and cause some type of harm. For example, Protists that live in animals and cause malaria.

Keystone Species

  • A Keystone Species is a species that is very important to its environments well being that you might not of otherwise noticed.
  • They keep other species in check that might otherwise out compete everything else around and grow in size while taking over the area while the other species shrink to very small population sizes.

Ecosystem Engineer

  • An Ecosystem Engineer is a type of keystone species that produces and maintains certain ecosystems or important areas of ecosystems, For example, Beavers are Ecosystem Engineers because they build dams which make ponds and provide more water and habitat for other species.
This beaver dam provides more slower moving water that more species can use


  • Ecological Succession: The replacement of one group of species by another group of species over time.
  • Primary Succession: Ecological Succession on surfaces that are initially lacking soil. This can take place on mostly any rock in the woods, what happens is that mosses and lichens start to colonize on the rock because they don't need soil. Overtime they produce acid that breaks down the rock and they get their nutrients that way. That acid then erodes the rock. This can occur after wild flowers or newly exposed rock. Once they die larger plants will grow on them and this repeats all the way up to full grown trees one day.
  • Soil is formed when the mosses and lichens die on top of the rock and mix with the nutrients they eroded from the rock, then as this repeats it starts to pile and make a layer on the rock, which then plants can use to grow.
  • Weeds, Grasses, and Wildflowers make good mid-successional plants due to the fact that they can survive well in the nutrient poor soil, and can survive in the open sunny areas succession takes place. Even better when they die and decompose they make the soil more rich in nutrients and better suitable for larger plants.
  • Secondary Succession: This takes place in areas that have gone through loss but still have soil. This may happen after forest fires, or hurricanes, or even abandoned farm land. This takes place the same way primary succession does but there is already soil there fit for short grasses and flowers.
  • Pioneer Species: These species colonize new areas fast and live well in full sunshine. These grow well in sunshine so once they grow to full size new ones can't grow due to the shade made by the older ones, instead now Beech and Maple trees start to grow in the shade and eventually out compete the smaller trees. An example of a Pioneer Species would be Aspen and Cherry trees.
  • Aquatic Succession: In oceans and inter tidal zones the rock that is exposed some times gets disturbed by storms and wipes the rock clean on all sides or turns it over. This provides a new surface for algae to survive and soon after barnacles start to inhabit the area to, if it isn't disturbed again it could soon become a permanent home for barnacles and mussels.

Friedland, Andrew, and Rick Relyea. "Chapter 6." Environmental science for AP. 2nd ed. W.H. Freeman, 2015. 211-215. Print.

Latitude, Time, Area, and Distance, and how they affect communities

  • Latitude: The farther you get away from the equator either north or south, the number of species present declines. For example an area in the southern latitudes of the U.S. holds about 12,000 species while the same area in northern Canada holds about 1,700 species.
  • Time: As well as latitude the time that an ecosystem has been around affects how many species is present. Lake Baikal in Siberia has 580 species of invertebrates in its Benthic zone, however the Great Slave Lake in northern Canada has about 4 species of invertebrates in its Benthic zone. Lake Baikal is more then 25 million years old , while the Great Slave Lake in Canada is only a few 10's of thousands years old.
  • Island Biogeography: This demonstrates the importance of habitat size as well as distance in determining species richness. Simply a larger island will have more species because there is more land to survive on, and on the other hand an island that is close to the shore of a country will have more species then one that is far out in the ocean, so the best island would be a reasonably close and large one. This would have more species then a farther one out to sea and smaller island.
Due to the small size of this island it wouldn't have much variety on it

Why do larger habitats contain more species?

  • 1 - Migrating Species are more likely to find larger habitats then smaller ones.
  • 2 - At any given latitude larger habitats can support more species, there is greater diversity on them and are less prone to extinction.
  • 3 - Larger habitats contain more environmental conditions, some species prefer different types of environment.
  • As the area of the island increases, the species number increases as well.
  • This helps conservationists determine which islands to protect, there are many islands in the country that are better suited for life then the area surrounding it, so now they will protect the island.

Friedland, Andrew, and Rick Relyea. "Chapter 6." Environmental science for AP. 2nd ed. W.H. Freeman, 2015. 189-216. Print.


Created with images by tpsdave - "africa safari elephants" • rihaij - "wild geese flock of birds winter" • Unsplash - "elk field wildlife" • sethink - "lightning storm weather" • Zaimful - "sunrise pond fog" • Eu_go - "Mountains" • fvfavo - "Lion" • uits - "Porcupine" • Jeff Hudgins / Alabama - "Beaver Dam" • Curtis Abert - "Picture_0850" • thedailyenglishshow - "Island"

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