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Understanding Populations

Understanding Populations. Chapter 8 page 210. What is a population?. Population All the members of a species living in the same place at the same time. Ex: bass in an Ohio lake Reproductive group Refers to the group and the size. Properties of Populations. Described by

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Understanding Populations

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  1. Understanding Populations Chapter 8 page 210

  2. What is a population? • Population • All the members of a species living in the same place at the same time. • Ex: bass in an Ohio lake • Reproductive group • Refers to the group and the size

  3. Properties of Populations • Described by • 1.Size, 2. density, or 3. dispersion • Density • Is the number of individuals per unit area or volume. • Ex: number of bass per cubic meter of water in a lake • Dispersion • Is the distribution of its individuals within a given amount of space. • Even, clumped, random

  4. How does a population grow? • 1.Gains by births • 2.Loses by death • Growth rate • A change in the size of a population over a given period of time. • Equation • Change in pop size = births – deaths • Growth rates can be 0, +, or – • Do all young survive to reproduce?

  5. How fast can a population grow? • A species biotic potential is the fastest rate that its population can grow. • Reproductive potential • The maximum number of offspring that each member of the population can produce • EX: elephant 750 yrs to produce 19 million descendants vs. Bacteria produce that many in a few weeks • 1.Produce more at a time,2. reproduce more often, and 3. reproduce earlier in life. • Reproducing early shortens generation time.

  6. How fast - Continued…. • Exponential growth • populations grow faster and faster • Occurs in nature if plenty of food & space and no competition/predators • EX dandelions and starlings • Growth rate = change in population/time

  7. What limits population growth? • Carrying capacity– • Is the maximum population that the ecosystem can support indefinitely. • May increase above this but not for long. • Estimated by looking at average population sizes or observing a population crash. • EX: rabbit population in Australia 1859

  8. What limits growth- continued…… • Limiting resource – species reach carrying capacity when it consumes a resource at the same rate the ecosystem produces it. That resource is a limiting resources. Ex: what limits plants?

  9. What limits growth- continued…… • Competition • The member of a population use the same resources in the same way. As the population reaches carrying capacity the will compete with each other. • EX: mealworm larvae in a sack of flour. • Social Dominance or Territory • Territory includes space, shelter, food, breeding sites • Competition is part of natural selection.

  10. 2 types of population regulation • Causes of death in population may be either: • Density dependent – • Deaths occur more quickly in a crowed population. Limited resources, predation, disease • EX: pine trees growing close together get infected by disease carrying beetle. • Density independent • A certain proportion of the population dies regardless of the population's density. Sever weather, natural disasters • EX: winter storm froze crops and fruiting trees

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