Transcript Populations
Populations Chapter 15 Definition • Population – • Example – the human population of Grapevine, TX Characteristics of Populations • Population size – Number of individuals • Population density – Number of individuals in an area • Immigration – Organisms moving into a population • Dispersion – How individuals are arranged in space Types of Dispersion Population Growth = # births - # deaths – If more individuals are born than die, the population grows – If more individuals die than are born, the populations shrinks Carrying Capacity (K) • # of individuals the environment can sustain Carrying capacity What are some factors that would keep a population from going over their carrying capacity? Density-Dependent Factors • Limited Resources – – – – – – Food Water Shelter Competition Predation Parasitism • When limited resources become depleted, population growth slows Population cycles in the snowshoe hare and lynx Why do the numbers of predators and prey cycle up and down together? Density-Independent Factors • Environmental conditions that limit population growth – Weather (drought, floods, grass fires) – Climate – Human Disturbances r- and K-Strategists • r-strategists – – – – – Small Reproduce often and large numbers Unstable environment Exponential growth ex: mouse, bacteria, rabbits, fish • K-strategists – Large – Reproduce less frequently, in numbers that they can manage – parental care – Stable environment – Logistic growth – ex: elephant, bears, whales, horses Populations evolve because allele frequencies change • Things that change allele frequencies – Mutations – Gene flow – Non-random mating – Genetic drift – Natural selection Challenge #3 Population Dynamics T. Trimpe 2008 http://sciencespot.net/ Answer each question. 1. If a population of 50 cottontail rabbits produce 300 young in a year, what is the birth rate for this population? 2. True or False – If the birth rate < death rate, the population will increase in size. 3. What term refers to the movement of animals into a population? Rabbit Population Rabbit Population Study 4. Use the graph to answer these questions. B. In which year did the population increase the most? 500 # of Rabbits A. In which year did the population decrease the most? Data recorded at the end of each year. 600 400 300 200 100 0 1 2 3 4 5 6 Year 7 8 9 10 The answers are … 1. If a population of 50 cottontail rabbits produce 300 young in a year, what is the birth rate for this population? 300 rabbits per year 2. True or False – If the birth rate < death rate, the population will increase in size. False – The population would decrease. 3. What term refers to the movement of animals into a population? Immigration Rabbit Population Rabbit Population Study 4. Use the graph to answer these questions. B. In which year did the population increase the most? Year 1 500 # of Rabbits A. In which year did the population decrease the most? Year 4 Data recorded at the end of each year. 600 400 300 200 100 0 1 2 3 4 5 6 Year 7 8 9 10 Gene Flow • Migration of fertile individuals or gametes between populations • Reduces differences between populations Genetic Drift Change in allele frequency due to chance. Happens in small populations. Bottleneck Effect (Genetic Drift) Preserving Variation • Why are unfavorable alleles not eliminated from population? • Diploidy • Heterozygote advantage – Ex: sickle-cell allele and malaria Natural Selection • Darwinian fitness – contribution an individual makes to the gene pool of the next generation relative to the contributions of others • Modes of selection – Directional – Diversifying – Stabilizing Modes of Selection Directional Selection Diversifying Selection A limited resource is known as a A. B. C. D. Polygenic trait Logistic model Density-independent factor Density-dependent factor An organism that grows exponentially is A. B. C. D. Dispersed Polygenic An r-strategist A K-strategist _____ tends to happen in a population whose individuals have extreme traits. A. B. C. D. Random mating Directional selection Stabilizing selection Exponential growth A colony of bacteria that has limited food will undergo ______ growth. A. B. C. D. Exponential Logistic Natural random Which of the following is not a cause of genetic change? A. B. C. D. Genetic drift Random mating Natural selection mutation