STABILIZING WORLD POPULATION THE HUMAN POPULATION STABILIZING WORLD POPULATION Population Ecology & Human Population

WHAT IS POPULATION ECOLOGY: population – collection of individuals of same species in a given area whose members can breed with one another population ecology studies dynamics of species’ populations how these populations interact with environment Population Ecology & Human Population

WHAT IS POPULATION ECOLOGY: 3 important characteristics of a population are its: geographic distribution - describes area inhabited by a population population density = # of individuals unit area2 growth rate - increase or decrease of # individuals in a population over time Population Ecology & Human Population

Population Ecology & Human Population population changes global scale: change in population is due to # of births & deaths local populations: change in population is due to # of births, deaths, immigration (i), & emigration (e) Population Ecology & Human Population

WHAT IS POPULATION ECOLOGY: growth rate (r) – rate of change (increase or decrease) of a population’s size, expressed in %/yr growth rate = birth rate - death rate r = b - d Population Ecology & Human Population

Maximum Population Growth Biotic potential: maximum rate of increase under ideal conditions and affected by factors called life history characteristics Life history characteristics Age at first reproduction Reproductive fraction of life span Number of reproductive periods/events Number of offspring per reproductive event Large organisms (whales, elephants) have lesser biotic potentials Small organisms (microorganisms) have greater biotic potentials Population Ecology & Human Population

Reproductive Patterns and Survival Population Ecology & Human Population

Population Ecology & Human Population R-ADAPTED SPECIES short life rapid growth early maturity many small offspring little parental care little investment in individual offspring adapted to unstable environment pioneers, colonizers niche generalists Prey regulated mainly by extrinsic factors low trophic level Population Ecology & Human Population

Population Ecology & Human Population K-ADAPTED SPECIES long life slower growth late maturity fewer large offspring high parental care & protection high investment in individual offspring adapted to stable environment later stages of succession niche specialists predators regulated mainly by intrinsic factors high trophic level Population Ecology & Human Population

EXPONENTIAL GROWTH: J-SHAPED When bacteria divide at a constant rate & their #s are graphed, curve of exponential population growth has a characteristic J shape Streptococcus bacteria cell dividing exponential population growth – accelerating population growth that occurs when optimal conditions allow a constant reproductive rate Population Ecology & Human Population

EXPONENTIAL GROWTH: J-SHAPED under ideal conditions with unlimited resources, population will grow exponentially occurs when individuals in a population reproduce at a constant rate exponential growth curve – (J-shaped) graph that shows phase of population growth during which size of population doubles regularly within a certain time period Population Ecology & Human Population

LOGISTIC GROWTH: S-SHAPED CURVE logistic growth curve most populations go through a # of growth phases, which can be represented on a logistic growth curve. steady state – portion of a logistic growth curve in which the average growth rate is zero Population Ecology & Human Population

LOGISTIC GROWTH: S-SHAPED CURVE exponential growth does not continue for very long as resources become less available, growth of a population slows or stops occurs when a population's growth slows or stops following a period of exponential growth. Population Ecology & Human Population

LOGISTIC GROWTH: S-SHAPED CURVE carrying capacity (K) – largest population a particular environment can support sustainably (long-term) assuming that there are no changes in that environment Paramecium is a unicellular protist, a kind of microorganism Population Ecology & Human Population

Population Ecology & Human Population CARRYING CAPACITY carrying capacity – size of population during steady state portion of logistic growth curve largest # of individuals of a population that an environment can support sustainably when a population reaches carrying capacity (K), its growth levels off average growth rate= zero # varies from species to species. Population Ecology & Human Population

Population Ecology & Human Population CARRYING CAPACITY Population Ecology & Human Population

environmental resistance carrying capacity (K) population stabilizes Population size exponential growth biotic potential Time (t)

Number of sheep (millions) 2.0 Population overshoots carrying capacity Carrying capacity 1.5 Population recovers and stabilizes Population runs out of resources and crashes Number of sheep (millions) 1.0 Exponential growth .5 Figure 5.12 Logistic growth of a sheep population on the island of Tasmania between 1800 and 1925. After sheep were introduced in 1800, their population grew exponentially, thanks to an ample food supply. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep. 1800 1825 1850 1875 1900 1925 Year Fig. 5-12, p. 111

2,000 Population overshoots carrying capacity 1,500 Population crashes Number of reindeer 1,000 500 Carrying capacity Figure 5.13 Exponential growth, overshoot, and population crash of reindeer introduced to the small Bering Sea island of St. Paul. When 26 reindeer (24 of them female) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd size had soared to 2,000, overshooting the island’s carrying capacity. This led to a population crash, when the herd size plummeted to only 8 reindeer by 1950. Question: Why do you think this population grew fast and crashed, unlike the sheep in Figure 5-12? 1910 1920 1930 1940 1950 Year Fig. 5-13, p. 112

WHAT IS POPULATION ECOLOGY: survival of a species depends on how well it can (as a group) reproduce utilize available resources adapt to a changing environment Population Ecology & Human Population