If I want to be successful by the end of the unit I will be able to: Compare and contrast types of symbiotic relationships Describe a population and its qualities Describe exponential and logistic growth Identify factors that determine carrying capacity Compare and contrast density dependent and independent factors

Species Interactions

Types of Species interactions Species interactions are the backbone of communities Most important categories Commensalism = one species benefits , one unaffected Mutualism = both species benefit Parasitism = one species benefits and the other is harmed Competition = both species are harmed Predation= one species benefits and the other is harmed S Y M B I O

Competition Competition = relationship where multiple organisms seek the same limited resources they need to survive: Food - Water Space - Shelter Mates - Sunlight Intraspecific competition = between members of the same species High population density = increased competition Interspecific competition = among members of 2 or more species

Predator-Prey Relationships Predation can drive population dynamics (cyclic) Increased prey populations increases predators Predators survive and reproduce Increased predator populations decrease prey Decreased prey population causes starvation of predators Decreased predator populations increases prey populations

POPULATION ECOLOGY

Population Dynamics Population: All the individuals of a species that live together in an area Niche: Narrow range where a species fits within a habitat. Demography: The statistical study of populations, allows predictions to be made about how a population will change Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

How are populations described? Three Key Features of Populations Size Density Dispersion Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Size: number of individuals in an area Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Growth Rate: Birth Rate (natality) - Death Rate (mortality) How many individuals are born vs. how many die Birth rate (b) − death rate (d) = rate of natural increase (r) Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Density: measurement of population per unit area or unit volume Pop. Density = # of individuals ÷ unit of space Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

HOW DO YOU AFFECT DENSITY? Immigration: movement of individuals into a population Emigration: movement of individuals out of a population

HOW DO YOU AFFECT DENSITY? Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases Examples: disease, competition, parasites

HOW DO YOU AFFECT DENSITY? Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density Examples: temperature, weather

Factors That Affect Future Population Growth Immigration + + - Population Mortality Natality - Emigration

Three Key Features of Populations Dispersion: describes the spacing of organisms relative to each other Clumped Uniform Random Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Population Dispersion

Check Point 3- three key features of populations, describe each one 2- two types of limiting factors, examples of each 1- one buzz word to describe the spacing of organisms relative to each other

How Are Populations Measured? Population density = number of individuals in a given area or volume Count all the individuals in a population

How Do Populations Grow? Idealized models describe two kinds of population growth: Exponential Growth When resources are unlimited, a population can experience exponential growth, where its size increases at a greater and greater rate. Does not stop Logistic Growth Logistic growth of a population size occurs when resources are limited, thereby setting a maximum number an environment can support. Until it reaches its carrying capacity

Exponential Growth Curve Figure 35.3A

Logistic Growth Curve

“Booms” and “Busts”

Carrying Capacity (k): The maximum population size that can be supported by the available resources There can only be as many organisms as the environmental resources can support Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Factors Limiting Growth Rate Declining birth rate or increasing death rate are caused by several factors including: Limited food supply The buildup of toxic wastes Increased disease Predation

Reproductive Strategies R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches, weeds, bacteria

Reproductive Strategies K Strategists Long life span Large body size Reproduce slowly Has few young Provides parental care Ex: humans, elephants

A survivorship curve is a graph showing the number of individuals surviving to each age for a given species or group (e.g. males or females). Curve usually based on a standardized population of 1000 individuals Survivorship Curves

Survivorship curves can be classified into three general types Type I, Type II, and Type III I II III 50 100 1 10 1,000 Percentage of maximum life span Number of survivors (log scale)

Type I curve typical of animals that produce few young but care for them well . Death rate low until late in life where rate increases sharply as a result of old age Humans, elephants Type I curve

Type II curve has fairly steady death rate throughout life Death is usually a result of chance processes over which the organism has little control Rodents Type II curve

Type III curve typical of species that produce large numbers of young which receive little or no care Survival of young is dependent on luck. Example: Larvae released into sea have only a small chance of settling on a suitable substrate. Once settled however, prospects of survival are much better and a long life is possible. Type III curve