Chapter 9 Population Dynamics, Carrying Capacity, and Conservation Biology Mrs. Cook Environmental Science

Population Dynamics Characteristics of a Population 1.Size- number of individuals 2.Density- number of individuals in a certain space 3. Age distribution- proportion of individuals of each age in a population

How Does a Population Grow? 1.Births 2.Deaths 3.Immigration 4.Emigration A population gains individuals by birth and immigration and loses them by death and emigration. Population change= (Births + Immigration) – (Death + Emigration)

How Does a Population Grow? Growth rate - the increase in the size of a population over a given period of time. Growth rates change over time because birth rates and death rates increase or decrease. Therefore, growth rates can be positive, negative, or zero.

How Does a Population Grow? If the average number of births are equal to the average number of deaths, then The growth rate = zero Example: A pop. would remain the same size (GR = 0) if each pair of adults produced exactly two offspring. A pop. shrinks (GR = Negative #) if the adults are not replaced when they die

How Does a Population Grow? Populations usually stay about the same size from year to year because various factors kill off individuals before they reproduce. This controls the size of a population. Determine how the population evolves.

Reproductive Potential Biotic potential - is the fastest rate at which a population can grow. This is limited by reproductive potential. Reproductive potential (r) is the maximum number of offspring that a given organism can produce. Increases when you have >1 at a time Increases if you start earlier Increases if the generation time is short Increases if little time/energy into offspring Decreases if it takes a long time to reach sexual maturity

Reproductive Potential Examples: 750 years for a pair of elephants to produce 19 million descendents While bacteria could produce that in a few days or weeks.

Exponential Growth Exponential growth is growth in which the rate grows faster and faster (J-curve) Occurs in nature only when populations have plenty of food and space and have no competition or predators. Ex. Population explosions of bacteria or molds on a new source of food.

Exponential Growth A large number of individuals is added to the population in each succeeding time period.

Logistic Growth Exponential at first… Slowing as the population encounters environmental resistance “S- shaped curve” Population size (N) Time (t)

Limits to Population Growth Resources are used up Food Light Space The environment changes Weather patterns Clear-cutting forests Water pollution Deaths increase or births decrease. Disease Lack of mates

Carrying Capacity (k) Carrying capacity (k) is the largest population that an environment can support. A population may overshoot this #, but it cannot stay at this increased size. Carrying capacity is difficult to predict or calculate exactly because ecosystems change.

Carrying Capacity (k) What if a population exceeds its Carrying Capacity? A population may use up resources and overshoot the “k” - known as a population BOOM. - Overshoot occurs due to… Reproductive Lag Time - Period needed for the birth rate to fall and the death rate to rise in response to overconsumption

Carrying Capacity (k) This lag can cause Dieback or Crash, known as a population BUST. Occurs unless the excess individuals… Switch to new resources Move to an area with more favorable conditions

Boom and Bust Effect 2,000 1,500 1, Number of reindeer Year

Resource Limits A species reaches its Carrying Capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource. Food Shelter Oxygen (aquatic ecosystems) That resource is called a limiting resource.

Competition with in a population Members of a population will compete for limiting resources Members may compete indirectly for social dominance or for a territory.

Population Regulation In density dependent regulation, deaths occur more quickly in a crowded population than in a sparse population. Happens when individuals are densely packed together. The Plague - “Black Death” Chestnut blight Pine beetles

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Population Regulation In density independent regulation, a certain proportion of a population may die regardless of the population’s density. Affects all populations in a general or uniform way. Severe weather and natural disasters Wildfires Floods Hurricanes

Predation and Population Control Possible explanation for the 10-year population cycles of Hare and Lynx -Lynx preying on hares reduce their population -Shortage of hares reduces the lynx population -Lower # of Lynxes, hares increase -Lynx pop. Increases due to greater food supply

The Lynx-Hare Cyclic Cycle Population size (thousands)Population size (thousands) YearYear Hare Lynx

Reproductive Patterns and Survival r-selected species (opportunists) r-selected species (opportunists) Reach reproductive age early Have many offspring each time they reproduce Short generation times little or no care to the offspring Short lives- less than a year life span - overcome massive loss of offspring by producing so many unprotected offspring that a few will survive.

Reproductive Patterns and Survival r-selected species algae Bacteria Rodents Annual plants Insects *Opportunists Reproduce and disperse quickly when conditions are favorable Usually go through rapid boom-and-bust cycles

Reproductive Patterns and Survival r-selected species

Reproductive Patterns and Survival r-selected species

Reproductive Patterns and Survival k-Selected Species (competitor) Reproduce late in life Few offspring Offspring develop inside mother where they are safe Long generation time Put energy into protection and nurturing until young reach reproductive age -Young are cared for by one or both parents Thrive best in constant environments

Reproductive Patterns and Survival k-Selected Species (competitor) Called k-selected species because they tend to do well in competitive conditions when their population size is near the carrying capacity (k) of their environment. Large mammals (elephants, whales, humans) Birds of prey Large and long-lived plants (oak, redwood, tropical rain forest trees) Can be prone to extinction

Reproductive Patterns and Survival k-elected Species

CBS Population Survival

Reproductive Patterns and Survival Survivorship Curves Shows the number of survivors at each age group of a particular species Late Loss: k-selected species, reduced juvenile mortality Ex: Humans and elephants Early Loss: r-selected species, high juvenile mortality Constant Loss: face mortality at all ages Songbirds, lizards, small mammals

Percentage surviving (log scale ) Age

Conservation Biology Sustaining wildlife populations Goals: Investigate human impacts on biodiversity Develop practical approaches to maintain biodiversity Key Topics: Endangered species management Wildlife reserves Ecological Restoration Environmental Ethics

Conservation Biology Biodiversity is necessary to all life and should not be reduced by human actions Humans should not hasten extinction The best way to preserve biodiversity is to protect intact ecosystems and provide habitat

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