Understanding Populations Chapter 8 Environmental Science Population l

Understanding Populations Chapter 8 Environmental Science

Population l l l All the members of a species living in the same place at the same time Organisms from the same population breed with each other, usually not other populations Three ways to describe populations l l Size Density l l Number of individuals per unit area or volume Dispersion l Distribution or arrangement of individuals within a given amount of space

How does a population grow? l Growth rate l Change in the size of a population over a given period of time Change in population size = Birth rate - Death rate

How fast can a population grow? l Reproductive potential l l Maximum number of offspring that each member of a population can produce Some species have a higher reproductive rate than others Biotic potential l Fastest rate that a population can grow Reproductive potential increases when individuals: l Produce more offspring at a time l Reproduce more often l Reproduce earlier in life § Bacteria (short generation time), humans (longer generation time)

Exponential Growth l When a population grows faster and faster l Example: Dog gives birth to 6 puppies § l Next generation – 18 puppies and so on Occurs in nature when: l l Plenty of food and space No competition or predators

What limits population growth? l Carrying capacity l l l The maximum population that the ecosystem can support indefinitely Populations may go over this number Carrying capacity can be estimated, not exact

What limits population growth? l Resource limits l Limiting resource l l A resource that is being consumed at the same rate it is being produced Example: plant growth limited by…. . § § § l Water Sunlight Mineral nutrients Supply of the most limiting resource determines the carrying capacity of an ecosystem

What limits population growth? l Competition within a population l l Species in a population use the same resources in the same ways (ex. Food) Indirect competition l Competing for their territory § l Area defended by one or more individuals against others Territories are valuable to an organism § § Space Shelter Food Breeding sites

Growth Rate l l l Math Practice Page 201 Worksheet

Population Regulation l Density dependent l Deaths occur quickly in crowded populations § § § l Limited resources Predation Disease Density independent l l Portion of population will die regardless of density Possible causes § § Severe weather Natural disasters

Assignment l l l Page 202 Section 1 Review # 2 -5

How Species Interact with Each Other l Niche l l Unique role of a species within an ecosystem Includes: l l Different from habitat l l l Species’ physical home Environmental factors necessary for survival Interactions with other organisms Habitat is only a location Niche is a pattern of how the habitat is used Can be thought of as a job in an ecosystem

Ways Species Interact l Competition l l l Different individuals or populations attempt to use the same limited resource Can occur within a species or between a species Indirect competition l l Example – one insect feeds on a plant during the day and another insect feeds on the same plant at night Adaptations can occur over time to decrease competition § § Using less of a niche than they are capable of using Similar species will divide up the niche to “share space”

Ways Species Interact l Predation l Predator l l Prey l l l Feeds on another organism Organism that is fed upon Organisms can be a predator and the prey Some predators will only eat specific types of prey

Ways Species Interact l Parasitism l Parasite l l Host l l Organism that lives in and feeds on another organism Organism the parasite takes its nourishment from Examples of parasites l l l Ticks Fleas Tapeworms

Ways Species Interact l Mutualism l l l Close relationship between two organisms where both benefit Example – bacteria in your intestines and you Commensalism l l Relationship where one species benefits and the other is neither helped nor harmed Example – Birds nesting in trees (causing no harm to the tree)

Ways Species Interact l Symbiosis l l Relationship where two organisms live in close association Coevolution l l l Relationships may coevolve over time Can reduce the harm to an organism Can increase the benefit to an organism

Assignment l l l Page 209 Section 2 Review # 1 -5

Chapter 8 Review Questions l l Pages 211 -213 # 5 -18, 21 -23, 25, 31