Lecture 4

• the distribution and abundance of all organisms • the interactions among living organisms (= biotic factors) • the interactions between living organisms and their non-living surrounding environments (= abiotic factors)

species and their interactions with physical and chemical surroundings

The physical environment in which individuals of a species can be found

The role a species plays in its community - e.g how it gets NRG/nutrients - habitat requirements

• Biosphere (global processes) • ecosystem (NRG flux, cycling nutrients) • community (interactions among populations) • population (population dynamics the unit of evolution) • organism (survival and reproduction; the unit of natural selection)

a group of individuals belonging to one species that live in a particular area at the same time and where they share resources

Changes in population over time

• size • density • distribution or dispersion • demographics • sex ratio • age structure • survivorship

Number of individual organisms present in a location at one given time

smallest number of individuals that would still allow a population to persist or grow ensuring long-term survival

Number of individuals within a population per unit space

• normal social behaviors are deficient • unable to find mates/ mating behaviors don’t occur • genetic diversity falls • important community connections may be lost, affects other species

• normal social behaviors breakdown with overcrowding • disease spread increases • low food supply • increased human conflict • overuse of resources -> damage to environment

Spatial arrangement of individual organisms within an area

Clumped (common) - based on resources or habitat - animals Random - resources found throughout habitat with little competition - plants Uniform - individuals compete for resources and space - plants, nesting birds

Response to changes in sex ratio, age structure, survivorship

proportion of males to females - monogamous species, a 50/50 sex ratio is optimal

relative numbers of individual organisms in each age cohort within a population

• increasing rapidly • increasing slowly • stable • decreasing

patterns of survival at different life stages - Crude estimation of birth/death rates

Type I: few deaths at younger ages with most deaths at older ages - humans Type II: equal number of deaths at all ages - birds Type III: more deaths at younger ages and fewer deaths at older ages - amphibians (frogs)

Additions: 1. birth 2. immigration Subtractions: 1. deaths 2. emigration

• exponential growth model • logistic growth model

Steady growth rates (= r) cause exponential growth - gives a “J-shaped” curve - assumes unlimited resources - cannot be sustained indefinitely - e.g small populations growing under ideal conditions