Transcript Env Sci 8
Chapter 8 Understanding Populations 8.1 How Populations Change in Size 8.2 How Species Interact with Each Other Objectives • Describe the three main properties of a population. • Describe exponential population growth. • Describe how the reproductive behavior of individuals can affect the growth rate of their population. • Explain how population sizes in nature are regulated 8.1 What Is a Population • Population: All members of one species in one place, at one time. Ex• all the palm trees on an island • A school of fish 8.1 Properties of Populations • A population is a reproductive group because organisms usually breed with members of their own population. • Populations described in terms of: – Density: number of individuals of the same species per area. • Ex: the fish live in dense schools – Dispersion: arrangement of indiv. • Ex: – Even – Uniform – Clumped – in small groups – Random – anywhere 8.1 How does a Population Grow? Introduction In 1935, a decision was made to release 46 Merriam’s turkeys within the state of Wyoming. Prior to this decision, none of these turkeys existed within the state. You will predict how the population of these turkeys grows and changes under different conditions. 8.1 How does a Population Grow? • Linear Growth Model 1. Compute the size of the population of these turkeys in Wyoming using the following assumptions: a. Every year, 250 offspring are produced by the turkey population. b. No turkeys emigrate, or leave the area. c. There were no diseases, shortages of food, or shortage of space that limited the population. 2. Graph the turkey population over the nine generations. Generation is on the x-axis, population on the y-axis. 8.1 How does a Population Grow? • Linear Growth Model 8.1 How does a Population Grow? • Linear Growth Model Do you believe this is an accurate model of the growth of these models? Look at the three assumptions above. Give a reason why each assumption is flawed. What are two other possible variables that are not accounted for in this model? 8.1 How does a Population Grow? • Exponential Growth Model 1. Compute the size of the population of these turkeys in Wyoming using the following assumptions: a. No turkeys left the general area during the first five years. b. There was no disease, shortage of food or habitat limiting the population. c. There were equal numbers of females and males in each hatch. d. Each mature female produces 10 eggs per year. Each egg survives. e. Turkeys do not reach sexual maturity until they are one year old. f. All turkeys only survive five years. g. The original population of turkeys were each 1 years old and sexually mature. h. There were 23 females and 23 males originally in the population. How To Calculate It 8.1 How does a Population Grow? • Exponential Growth Model 1. Do you believe this is a more or less accurate model than the linear growth model? Explain why. 2. If this level of population growth within this same area were to continue, what would eventually happen to the turkeys? 3. List three possible variables or limiting factors that could affect this population’s growth that were not included in this model. 8.1 How does a Population Grow? • Populations change with life and death – Death = one less – Birth = one more • Growth rate: (the resulting population change) 8.1 How does a Population Grow? •Overtime, the growth rates of populations change because birth rates and death rates increase or decrease. •For this reason, growth rates can be positive, negative, or zero. 8.1 How Fast Can a Population Grow? • Reproductive potential(RP): is the maximum number of offspring that a given organism can produce. • Increases when an indiv. can reproduce: • more offsprings at one time • start earlier • more often –Bacteria high RP –Corpse Flower Low RP 8.1 How Fast Can a Population Grow? • Exponential growth: is logarithmic growth or growth in which numbers increase by a certain factor in each successive time period. To grow faster and faster – Must have lots of food and space, – no predators or competition. – Bacteria grow this way. 8.1 What Limits Population Growth? • Carrying capacity : largest population that an ecosystem can support. • difficult to predict or calculate exactly. – Limiting resource: controls the carrying capacity – Territory: area belonging to a population, organisms compete for territory. 8.1 Competition Within a Population • Members of a population use the same resources in the same way, so they must compete for them. –Directly who can eat more faster. –Indirectly competing for social dominance of a territory. 8.1 Two types of population Regulation • Density dependent – Deaths occur more frequently in crowded areas than in a sparse population. Ex: • Predation – Pop.A increasing can lead to Pop.B increasing, and eating Pop.A • Disease - easily spread if close together • Density independent – Deaths occur regardless of dispersion affecting all populations. Ex• Natural disasters 8.1 How Fast Can a Population Grow? NOT NOTES • A Female sea turtle lays 2,000 eggs in her life, do they all live? No! They are smooshed, eaten and otherwise destroyed before they become adults. What would happen to the population of turtles if they all lived? It would be huge. Out of control. • The things that kill the baby turtles are the factors that control population size 8.1 How Fast Can a Population Grow? NOT NOTES • The Corpse Flower grows for 10 years as one giant leaf. Each year it grows a new leaf, and saves up energy in its root. After 10 years it grows one giant flower, which smells like a dead animal. And this flower leads to seeds. 8.1 Classwork : Review Questions • Page 225 #9,10,11,12 – answer with one sentence and the letter Page 226 #21-23 – complete sentences. Be sure to explain yourself. Chapter 8 8.1 How Populations Change in Size 8.2 How Species Interact with Each Other 8.2 How Species Interact with Each Other A. An Organism’s Niche 1. Def: the unique role of a species in an ecosystem in terms of : a) b) c) d) Physical use Behavior Interactions Particular “job” 2. Ex: A lion’s niche, Your niche. An organism’s habitat is a location. However, a niche is an organism’s pattern of use of its habitat. 8.2 How Species Interact with Each Other 8.2 How Species Interact with Each Other A. Competition 1. Def: Different individuals or populations try to use the same resource. 2. “niche overlap” – When two populations compete. a) Ex: wolves and brown bears hunt Bison. Wolves primarily hunt Bison, Bears primarily hunt salmon, occasionally hunt bison. 3. Avoid direct competition a) hunting at different times ( indirect competition). 8.2 How Species Interact with Each Other B. Predation 1. An organism feeds on another organism. 2. Some predators are also prey. Ex. a) Chicken eats insects, I eat chicken b) Tuna eats other fish, sharks eat tuna 8.2 How Species Interact with Each Other B. Predation 3. Some predators eat only a specific kind of prey 8.2 How Species Interact with Each Other C. Parasitism 1. The parasite: feeds on the host. (organism that parasite lives and feeds on it). 2. Similar to predators, but they have an advantage if they don’t kill their host. Why? 1. Then they can keep taking Parasite Host the energy Mosquito Tapeworm Mistletoe person Dog tree 8.2 How Species Interact with Each Other D. Commensalism 1. Def: A relationship in which one species is helped, the other is not affected Species A: not affected Species B: helped Whale Barnacle – a home, movement. Tree Orchid – more exposure to light Anemone Clownfish - protection 8.2 How Species Interact with Each Other E. Mutualism 1. A relationship in which both species helps the other. 2. Often they need the other to survive Species A: helped Species B: helped Bacteria – warm place w/ food Person – our food is digested Ants – shelter and food Acacia tree - protection Crocodile – cleaning Bird - food 8.2 How Species Interact with Each Other F. Coevolution 1. A relationship in which 2 species interact so closely that they evolved together to reduce the harm or improve the benefit of the relationship. 2. Ant and aphid 3. Fly and flower G. Symbiosis 1. A relationship in which two species live in close association. 2. At least one species benefits. Classwork Write questions and answers.