TOPIC 3 Population Ecology 3 a Density distribution

TOPIC 3 Population Ecology 3 a – Density, distribution, & Survivorship

TOPIC 3 Key Concepts • What is population density? • How can populations distributed? • What are the reproductive strategies? • What do survivorship curves show? Key Terms • Population density • Population distribution – Random – Clumped – Uniform • • • Immigration/Emigration Natality/Mortality r-strategist K-strategist Survivorship

Population • Recall - what is a population? number of individuals in an area • Population size is the number of individuals in a population at a given time • What factors might affect population size? Immigration, emigration, births, deaths

Population Density • Population density is the number of individuals in a population per unit area. • EX. INSC pop = 900 INSC Area = 2, 400 m 2 population density = 900/2400 =. 375/m 2 • What would the benefits/drawbacks of having a high population density be? BENEFITS v Survival v Mating v Work together DRAWBACKS v Competition for resources (food, light, water, etc. ) v Disease

Population Distribution • Population Distribution describes how individuals are arranged in an area. • In a random distribution individuals are arranged in no pattern • In uniform distribution individuals are evenly spaced throughout an area • In clumped distribution individuals are grouped together in smaller clusters

Population Distribution Clustered or clumped in groups UNIFORM: spaced more or less evenly No predictable pattern

Population Distribution What factors might affect distribution? Ex. 1: dandelions and other plants that have winddispersed seeds. The seeds spread widely and Random sprout where they happen to fall, in favorable environment. Ex. 1: Plants that secrete toxins to inhibit growth of nearby individuals—a phenomenon called allelopathy. Uniform Ex. 2 animal species where individuals stake out and defend territories. Ex. Plants that drop their seeds straight to the ground—such as oak trees Clumped Ex. 2 Animals that live in groups—schools of fish or herds of elephants.

Population Growth • The increase in number of individuals in a population • Populations increase when more individuals enter than leave the group – How might individuals enter a population? Immigration, births, – How might individuals leave a population? Emigration, deaths

Immigration and Emigration • Immigration is the movement of individuals into a population • Emigration is the movement of individuals out of a population • Migration is the seasonal movement of individuals and populations

Natality and Mortality • Natality is the birth-rate of a population • Mortality is the death-rate of a population • Which of these terms would be higher when a population is growing? Natality Declining? Mortality

Calculating Population Growth • Population growth can be expressed with the formula: (individuals added) – (individuals subtracted) • What two factors add to a population? • What two factors subtract from a population? • Rewrite the population growth formula to include all factors.

REPRODUCTIVE STARTEGIES Reproductive strategies: behavioral, physical +parenting adaptations that to increase survival of young. r-strategists vs K-strategist Comparison

r-strategists Characteristics: – Usually small, prey – Have many, small offspring • So they have a high population growth rate – Little to no parental care – Reproduce at an early age – Most die before reaching reproductive age – Have a generalist niche • So they can live in unstable conditions – Populations fluctuate far above and below their carrying capacity.

K-strategists Characteristics: – Usually larger organisms – Have fewer, larger offspring • So they have a lower population growth rate – High parental care – Later reproductive age – Most offspring survive to reproductive age – Have a specialist niche • and are adaptable to stable environmental conditions. – Populations size is fairly stable and usually close to carrying capacity (K).

Reproductive Strategies & Survivorship Curves • Survivorship curves show different patterns of deathrates for populations • Some populations have higher death-rates as they get older (type I) • Other populations have higher death-rates when they are younger (type III) • Populations with type II curves have stable death-rates • REPRODUCTIVE STRATEGIES play a major role in determining survivorship curve of a species.

Survivorship Strategies & Curves What are examples of each type of pattern? TYPE 1 KOALA, HIPPO, ELEPHANT TYPE 2 SONG BIRDS, SALAMANDARS, RODENTS TYPE 3 ROACH, BUNNIES, FROGS