Chapter 52 Population Ecology Scope of Ecology Ecology

Chapter 52 ~ Population Ecology

Scope of Ecology ¡ Ecology l The study of the interactions of organisms with l Habitat - Place where an organism lives Population - All the individuals of a species within a particular space Community – Various populations of multiple species interacting with each other Ecosystem - Community interacting with the environment Biosphere - All the communities on Earth whose members exist in air and water and on land 2 l l Other organisms and the physical environment

Demographics of Populations Population characteristics ¡ ¡ Density~ # of individuals per unit of area l counts l sample size estimate l indirect indicators l mark-recapture Dispersion~ pattern of spacing l random~ unpredictable, patternless spacing l l clumped~ patchy aggregation uniform~ even spacing

Estimating Population Size The Mark-and-Recapture Technique ¡ 4

Let’s Try an Example! ¡ ¡ ¡ Twenty individuals are captured at random and marked with a dye or tag and then are released back into the environment. Therefore s = # of animals marked = 20 At a later time a second group of animals is captured at random from the population 5

Let’s Try an Example! ¡ 6

Population Growth Models Demography: factors that affect growth & decline of populations ¡ ¡ Birthrate (natality, fecundity)~ # of offspring produced Death rate (mortality) Age structure~ relative number of individuals of each age Survivorship curve~ plot of numbers still alive at each age

Survivorship curves Survival per thousand 1000 Human (type I) Hydra (type II) 100 II. Constant mortality rate throughout life span Oyster (type III) 10 1 0 25 What do these graphs indicate regarding species survival rate & I. High death rate in strategy? post-reproductive years 50 75 Percent of maximum life span 100 III. Very high early mortality but the few survivors then live long (stay reproductive)

Number of survivors (log scale) Ideal Survivorship Curves I 1, 000 100 II 10 III 1 0 50 Percentage of maximum life span 100

Demographics of Populations ¡ Survivorship Curves l Type I ¡ l Type II ¡ l Characteristic of a population in which most individuals survive past the midpoint of the life span and death does not come until the end of the life span Death is linear over time (unrelated to age) Type III ¡ Typical of a population in which most individuals die very young 10

Population Growth Models ¡ ¡ Exponential model (blue) • idealized population in an unlimited environment (Jcurve); r-selected species (r=per capita growth rate) Logistic model (red) • carrying capacity (K): maximum population size that a particular environment can support (S-curve); K-selected species

Population life history “strategies” ¡ ¡ r-selected (opportunistic) Short maturation & lifespan Many (small) offspring; usually 1 (early) reproduction; no parental care High death rate ¡ ¡ K-selected (equilibrial) Long maturation & lifespan Few (large) offspring; usually several (late) reproductions; extensive parental care Low death rate

Regulation of Population Size ¡ ¡ Density-independent Factors l The population density does not influence the intensity of the factor’s effect ¡ Natural disasters ¡ Weather/Climate Density-dependent Factors l The percentage of the population affected increases as the population density increases ¡ Competition ¡ Predation ¡ Parasitism ¡ Stress/Overcrowding ¡ Waste Accumulation