POPULATION AND COMMUNITY ECOLOGY

COMPLEXITY OF NATURE

POPULATION ECOLOGY “study of factors that cause populations to increase or decrease Population Size a. (births and immigration) - (deaths and emigration)

POPULATION CHARACTERISTICS a.Population size b.Population density c.Population distribution d.Population sex ratio e.Population age structure

POPULATION SIZE a.Total number of individuals within a given area at a particular time b.Dependent upon density-dependent and density-independent factors c.Density dependent - depends on how dense the population is - limiting resources ex) plants – nitrogen and phosphorus animals - food - carrying capacity( K): helps in predicting how many individuals a population can sustain

d. density-independent factors - does not depend on how dense the population is - ex) tornado, floods, fires

POPULATION DENSITY a.Number of individuals per unit of area b.Helps scientists estimate if a species is rare

POPULATION DISTRIBUTION a.How individuals are distributed throughout b.Random, uniform, clustered

POPULATION AGE STRUCTURE a.How many individuals fit into a particular age category b.Predicts how rapidly a population will grow

POPULATION GROWTH MODELS a.Growth rate – (births – deaths) in a given time period - intrinsic growth rate * unlimited resources available (r) * high population growth rate b. Exponential growth model - rapid growth - j shaped curve - continuously increase population growing at a fixed rate

c. Logistic growth model (k) - incorporates limits on population growth (limiting resources) - s shaped curve - predicts population growth subject to density-dependent constraints - overshoot - die-offs (population crash) - predation (lynx and the hare) /

REPRODUCTIVE STRATEGIES AND SURVIVORSHIP CURVES a.K-selected species (elephant) - low intrinsic growth rate - large organisms, late reproductive maturity, produce few offspring, provide parental care b. R-selected species (dandelions, house mice) - high intrinsic growth - rapid population growth with overshoots and die-offs - small organisms, early reproductive maturity, reproduce frequently with lots of offspring, little or no parental care

c. Survivorship curve – distinct patterns of survival over time

COMPETITION “struggle of individuals to obtain a limiting resource” a.Competitive Exclusion Principle - two species competing for the same limiting resource cannot coexist - having the same realized niche can lead to extinction of one species

b. Resource partitioning - two species divide a resource based on behavior and morphology - ex) birds that eat different seeds - 3 types * temporal * spatial * morphological

PREDATION A.One species as a resource of another species B.Four types - true predators - herbivores - parasites - parasitoids C. lynx-hare relationship D. Defenses - hiding, reduced movement, chemical toxins, thorns, camouflage

MUTUALISM “benefits two interacting species by increasing both species’ chances of survival or reproduction” a.Examples - pollination - coral reefs and algae - acacia trees and ants

COMMENSALISM “one species benefits but the other is neither harmed nor helped” a.Example - birds using trees as a perch

KEYSTONE SPECIES “species that plays an important role in its community” Exist in low numbers Types a. predators b. sources of food c. mutualistic species d. provider of other essential services

Examples a. sea stars (Pisaster ochraceus) b. flying fox c. beavers (ecosystem engineer)

SUCCESSION Ecological succession – predictable replacement of one group of species by another group of species over time Primary Succession a. surfaces that are devoid of soil

Secondary Succession a. areas that have been disturbed but have not lost their soil b. pioneer species

FACTORS AFFECTING SPECIES RICHNESS Determined by a. colonization of the area by new species b. speciation within the area c. losses from the area by extinction Factors above are influenced by a. latitude b. time c. habitat size d. habitat distance

Latitude a. the further away from the equator, the number of species decline b. no known reason Time a. longer a habitat exists, the more species there will be (colonization, speciation and extinction)

Habitat size and distance a. “Theory of Island Biogeography” - size: larger habitats contain more species * dispersing species are more likely to find larger habitats * larger habitats are less prone to extinction * larger habitats contain wider range of environmental conditions - distance: * islands further from land contain fewer species