Presentation on theme: "Population Distribution and Abundance (Chapter 9) Introduction"— Presentation transcript:
1 Population Distribution and Abundance (Chapter 9) Introduction Ecologists usually define a population as a group of individuals of a single species inhabiting a specific area.Characterized by the number of individuals and their density.Additional characteristics of a population include age distributions, growth rates, distribution, and local abundance.
2 Distribution LimitsPhysical environment limits geographic distribution of a species.
13 Distributions of Desert Shrubs Traditional theory suggests desert shrubs are regularly spaced due to competition.Phillips and MacMahon found distribution of desert shrubs changes from clumped to random to regular patterns as they grow.Young shrubs clumped for (3) reasons:Seeds germinate at safe sitesSeeds not dispersed from parent areasAsexual reproduction
14 Distributions of Desert Shrubs Phillips and MacMahon proposed as plants grow, some individuals in clumps die, reducing clumping.Competition among remaining plants produces higher mortality.Root zone competitionEventually creates regular distributions.
15 Clumped Distributions of Individuals on Large Scales (resource hot spots)
16 Animal Size and Population Density Relationship holds up within trophic levels (e.g., herbivores)
17 Plant Size and Population Density Plant population density decreases with increasing plant size.Underlying details are very different.Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities.
19 Commonness and RarityRabinowitz devised commonness classification based on (3) factors:Geographic Range of SpeciesHabitat ToleranceLocal Population SizePopulations that are least threatened by extinction, have extensive geographic ranges, broad habitat tolerances, and some large local populations.All seven other combinations create some kind of rarity.