Presentation on theme: "The Human Population and Its Impact"— Presentation transcript:
1 The Human Population and Its Impact Chapter 6The Human Population and Its Impact
2 Case Study New England Forests Come Full Circle Describe the temperate forest as seen by the Pilgrims.What happened to the temperate forest between 1620 and 1800s? Explain why this happened.What happened to the temperate forest between 1850 and Explain why this happened.What caused the appearance of the leaf beetle?What did the “outbreak” of the leaf beetle cause to happen?Explain the rise and fall of the goldenrod population.Explain the rise and fall of the other plant species.What was the first tree species to dominate and why?What led to the rise of the broadleaf deciduous trees?What does this process demonstrate?
4 Population Ecology Definition: Knowing the factors that affect a species’ population size helps to implement measures to improve its survival and reproduction.
5 Population Characteristics Population sizePopulation density
6 Population Characteristics Population DistributionOccupation of a population with respect to one another.RandomUniformClumped
7 Population Characteristics Population Sex RatioRatio of males to females.Number of offspring is primarily:Population Age StructureHow many individuals are in particular age categories.Large portion of older individuals …Large number of young individuals …
8 Factors that Influence Population Size Density-Dependent factorsFactors that influence the individual’s probability of survival and reproduction that depend on:Gause’s experiments
9 Limiting Resources Definition Carrying capacity - K Limiting resource decreases …Limiting resources for autotrophs …Limiting resources for heterotrophs …Carrying capacity - K
10 Density-Independent Factors Factors that influence the individual’s probability to survive that have nothing to do with the size of the population.Examples:
11 Growth Models To explain and predict changes in population size. Exponential Growth ModelPredict the population size at any moment of time.Growth rate - rDefinition:Intrinsic growth rate
12 Exponential Growth Model Nt = N0ertNt = population’s future sizeN0 = number of individuals currently in populatione is the base of the natural logarithmsr = intrinsic growth ratet = time passed
13 Do The MathConsider a population of rabbits that has an initial population size of 10 individuals.N0 = 10Let’s assume that the intrinsic rate of growth is 0.5 – 50%, which means that each rabbit produces and net increase of 0.5 rabbits each year.r = 0.5With this information, we can predict the size of the rabbit population a year from now.Nt = N0ertWhat about in 10 years?
14 Logistic Growth ModelPopulations do not experience exponential growth indefinitely, therefore:Initial growth is exponential but a slowing of growth as the population reaches the carrying capacity.S-shaped curve
15 Variations on the Logistic Growth Model OvershootDie-off
16 Predation as a Factor in Limiting Population Growth.
17 Reproductive Strategies K-selected speciesSpecies with a low growth rate.Population increases slowly until they reach the carrying capacity.Number of organisms is determined by the carrying capacity.Fluctuations in population are small.Characteristics:
18 r- Selected Species High intrinsic growth rate Do not typically remain near their carrying capacity.Rapid population growthOvershootsDie-offsCharacteristics:
19 Survivorship Curves Patterns of survival over time Type I Type III
20 MetapopulationsA group of spatially distinct populations that are connected by occasional movement of individuals between them.Corridors:
21 Species Interactions Factors that determine distributions of species: Community ecologyStudy of interactions of populations within a community.CompetitionDefinition:
23 Types of Resource Partitioning TemporalSpatialMorphological
24 Predation Use of one species as a resource by another species. True predatorsHerbivoresParasitesPathogensParasitoids
25 Prey DefensesTo avoid being eaten or harmed by a predator.
26 Symbiotic Relationships Relationship of two species that live in close association with each other.MutualismBoth interacting species benefit increasing both species chances of survival or reproduction.
27 CommensalismOne species benefits and the other is not harmed or helped.Cattle egret and cows and sheep.
28 Keystone SpeciesA species that plays a role in its community that is far more important than its relative abundance might suggest.
30 Types of Keystone Species Finding food for the communityMutualistic interactionsEcosystem engineers
31 Ecological Succession Predictable replacement of one group of species by another group of species over time.Terrestrial communitiesPrimary successionSecondary succession
32 Primary SuccessionGrowth of species on land that has never had growth before – no soil.
33 Primary SuccessionThe type of community that eventually develops is determined by the temperature and rainfall of the region.U.S.Forest in the EastGrasslands in the MidwestShrubland in the SouthwestIn some areas the number of species increases as succession proceeds.In some areas there are fewer late successional species than early ones.
34 Secondary SuccessionGrowth of species in areas that have been disturbed but have not lost their soil.Pioneer Species
36 Factors Influencing Species Richness The number and types of species present is determined by:Colonization of the area by new speciesSpeciation in the areaLoses in the area by extinctionFactors that affect these processes:LatitudeTimeSize of the habitatDistance of the habitat from the source of the colonizing species
37 Theory of Island Biogeography Theory that demonstrates the dual importance of habitat size and distance in determining species richness.Habitat sizeLarger habitats usually contain more species.Because:Distance from source of colonizing speciesDistance matters because: