Chapter 8 Notes Population Dynamics AP Env. Science

Ecocolumn Lab  Biosphere 2 Biosphere 2 Biosphere 2

POPULATION DYNAMICS?  Change in…  Population Size: Number of individuals  Population Density: Number of individuals in a certain space  What is the population density for the bunnies?  What is the population density of students in this classroom? 25 feet 30 feet

POPULATION DYNAMICS?  Population Dispersion: Distribution of the individuals of a population within a certain area  Clumping  Uniform Dispersion  Random Dispersion

POPULATION DYNAMICS?  Population Dispersion: Distribution of the individuals of a population within a certain area  Clumping  Uniform Dispersion  Random Dispersion

POPULATION DYNAMICS?  Population Dispersion: Distribution of the individuals of a population within a certain area  Clumping  Uniform Dispersion  Random Dispersion

LIMITS ON POPULATION GROWTH  Population controlled by…  Births  Deaths  Immigration  Emigration  Formula: Population Δ = (Births + Immigration) – (Deaths + Emigration)  These variables depend on various growth and decrease factors

INTRINSIC RATE OF INCREASE  Biotic Potential: Capacity for growth  Intrinsic Rate of Increase  “r”  Rate at which a population would grow if it had unlimited resources  i.e. Under ideal conditions, how fast could the population grow  High “r”  Reproduce early in life / Short generation times  Can reproduce many times  Have many offspring each reproductive cycle Some examples of high “r” Housefly: 5.6 trillion descendents within about 13 months Bacteria: 1 billion in 10 hoursBacteria

ENVIRONMENTAL RESISTANCE  High “r” is a dream  Rarely is/are ideal conditions found in nature  No population can grow indefinitely  There are always limits to population growth (see below)  What restricts a population’s intrinsic rate of increase, or biotic potential?  Environmental Resistance  All those factors that serve to limit a population  Population in a given place at a given time is the interplay between biotic potential and environmental resistance  Helps to determine carrying capacity (K)  Number of individuals of a given species that can be sustained indefinitely in a given space

Growth factors (biotic potential) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Abiotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Decrease factors (environmental resistance) Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Abiotic Biotic Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change

TYPES OF POPULATION GROWTH  EXPONENTIAL GROWTH  Starts out slowly and proceeds faster and faster  Occurs when a population has few (if any) limitations on it resources  Grows at the intrinsic rate of increase (r)  J-shaped curve  Rarely happens (for extended period of time) in nature Population size (N) Time (t) Exponential Growth

TYPES OF POPULATION GROWTH  LOGISTIC GROWTH  Exponential growth followed by a decrease in growth rate as the population reaches its carrying capacity (K)  Growth levels off and population stabilizes around carrying capacity  Growth typically fluctuates around the carrying capacity  S-shaped curve K Population size (N) Time (t) Logistic Growth

AFFECTS OF DENSITY ON GROWTH  DENSITY-INDEPENDENT FACTORS  Affect a population’s size regardless of the population density  Examples  Floods  Hurricanes  Unseasonable weather  Fire  Habitat destruction  Pesticide spraying

AFFECTS OF DENSITY ON GROWTH  DENSITY-DEPENDENT FACTORS  Factors whose effects on a population change with population density  Some factors have a greater effect as a population’s density increases  Examples  Competition  Predation  Parasitism  Disease

TYPES OF POPULATION CHANGE CURVES  In nature, there are four general categories of population fluctuations  STABLE  Population fluctuates slightly above and below its carrying capacity  Example: many species found in tropical rain forests where average temp and rainfall is fairly constant  IRRUPTIVE  Fairly stable population that occasionally explodes, or irrupts to a high peak and then crashes to a more stable lower level  The population explosion may be result of favorable weather, more food, fewer predators

TYPES OF POPULATION CHANGE CURVES  IRREGULAR  Population demonstrates chaotic behavior with no recurring pattern to population size  CYCLIC  Cyclic fluctuations in population size over a regular period of time  Lemming populations rise and fall every 3-4 years  Lynx and snowshoe hare populations generally rise and fall in a 10-year cycle

ROLE OF PREDATORS IN CONTROLLING POPULATION SIZE  Predator and prey undergo cyclic changes in their numbers  TOP-DOWN CONTROL: Hypothesis that predators cause the cyclical rise and fall of prey populations  We used to think predator periodically reduced prey population  Thus, predator population would go down  Fewer predators = prey population would rebound  Predators would soon rebound as prey became more plentiful Population size (thousands) Year Lynx Hare

ROLE OF PREDATORS IN CONTROLLING POPULATION SIZE  BOTTOM-UP CONTROL: Hypothesis that the prey cause the cyclical rise and fall of predator populations  Some prey that live on islands without predators also experience boom-and-bust cycles  Food supply increases = Rabbits have more to eat = Rabbit population increases  Rabbits overuse their food supply = Rabbits can’t get enough food = Rabbits die  Plants then recover, and the process begins again  Predators are affected by this rise and fall of the rabbit population

TYPES OF REPRODUCTIVE PATTERNS  Opportunists / r-Selected Species  High intrinsic rate of increase (r)  Reproduce early and put most of energy into reproduction (but not rearing)  Tend to be OPPORTUNISTS  Species with a broad ecological niche; Can live in many different places, eat a variety of foods, and tolerate a wide range of environmental conditions  Examples  Algae  Bacteria  Rodents  Annual plants  Insects  Do well in changing environments / habitats  Go through irregular and unstable boom-and-bust cycles r-Selected Species cockroach dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

TYPES OF REPRODUCTIVE PATTERNS  Competitor / K-Selected Species  Tend to do well in competitive conditions where their population is near the carrying capacity (K)  Usually follow a logistic growth curve  Reproduce late, but most of energy into nurturing/protecting just a few offspring  Thrive in ecosystems with fairly constant environmental conditions  Examples  Large mammals  Birds of prey  Large and long-lived plants Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species elephant saguaro K-Selected Species

SURVIVORSHIP CURVES  Different reproductive strategies result in different life expectancies  SURVIVORSHIP CURVES: Graph showing the number of survivors in different age groups for a particular species  Three generalized types of survivorship curves  Late Loss  High survivorship to a certain age  Higher mortality rates for older members  Early Loss  Survivorship is low in early life  Species tend to produce a lot of young, many of which die  Constant Loss  Fairly constant death rate at all ages Percentage surviving (log scale) Age

Estimating Animal Populations  Mark-Capture-Recapture  A.K.A. “The Lincoln Index”