Ecology III: Individuals and PopulationsEcology - the interrelationship between plants, animals, and the physical components of their environment.

•Biological levels of organization: cell, tissue, organ, system, organism (Old news!)

•Ecological levels of organization: population, community, ecosystem, {landscape}, biome, biosphere. (Defined below!)

•Population - a group of organisms of like species that live within a defined geographical region.•Community - plant and animal populations that live and interact with one another.

•Ecosystem - the living community and the physical aspects of their environment. May be described

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by using words such as: swamp, prairie, woodland, bog, fen.•Landscape - all the ecosystems visible as one scans the horizon. Most recently recognized. Existence doubtful.•Biome - major terrestrial assemblages of plants and animals. Descriptive terms; taiga, grasslands,

savannah, deserts.•Biosphere - Mother Earth

Population•Give several non-human examples. Be sure to use:

An individual species.A well-defined geographical distribution.

•Population Characteristics:•Size•Bottleneck effect in microevolution.

•Small populations have a better chance for extinction (if that is their goal).•Small populations - more inbreeding.

•Density:

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•May affect individuals ability to “find” one another.•Intraspecies competition for natural resources.

•Dispersion (From Animal Behavior Lab!)•Individuals may be randomly spaced (II), evenly spaced (regular) (I), or clumped (III).

(Plants)

I II III

•Clumping is the most probable pattern in nature.

Population Growth•Most populations in nature are stable and balanced. (Regardless of how many offspring are

produced!!)•Under certain conditions, however, population sizes can change dramatically.

Biotic Potential•The rate at which a population could grow if no limits were placed upon its growth.•The innate capacity for growth for any population is exponential. (Left below) exponential.

•This type of growth only occurs in natural populations when they are exploiting a new habitat (with beaucoups resources!)

•Examples: Algae in a new, manmade pond.Dandelions in a new lawn.Bacteria in a newly deposited fecal mass.

•Carrying Capacity (K)•The number of individuals in a population that can be supported at one site indefinitely.•This is a dynamic (rather than static) number because the resources in an environment change

constantly. (Student Examples)•The carrying capacity for an organism population is depicted below: (Population of Sheep in

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Tasmania)•Factors limiting further growth: food, shelter, light, mating sites, mates, water, waste accumulation, disease transmission. (These are called Limiting Factors!)

Density-Dependent and Density-Independent Effects

•Factors which limit the growth of populations.•These factors ( or effects ) are of two types:

1. Density-dependent factors2. Density-independent factors

Density-Dependent Effects •Shown effecting populations when competitiveness or interaction are involved. (ie. The population density determines the extent of the effect.)•Example: intraspecies competition for a natural resource. The more individuals there are, the greater the competition, the slower the population growth.

Density-Independent Effects•Effects which influence the entire population, regardless of density.

•Example: the effects of a hurricane on the palm trees in Dade Country, FL.

Harvesting•When humans are harvesting plant or animal populations, the best time to harvest is in the middle of the sigmoid curve. (The point of optimum yield). Why?

1. At a lower point, the reproductive potential of the population is reduced.2. At a higher point, the ecosystem’s resources are close to being depleted and the population could not sustain itself if left unchecked.

r and K Selection•Two different ecological species categories (r and K) distinguished by their strategies for success. (Success being their long-term presence in an ecosystem.)

r Strategy Species•high intrinsic rate of increase (r)•reproduce early and have many offspring•offspring are small, mature early, and receive limited or no

parental care, good offspring dispersal•found to undergo wild swings in their population numbers.•Examples: bacteria, ants, mosquitoes, mice, dandelions, oysters• energy used to make each individual is low•short life expectancy

K Strategy Species•low intrinsic rate of increase (r)•reproduce late and have few offspring•long life expectancy•offspring are large, mature slowly, and often receive intense parental care•populations are stable and normally found at the carrying capacity (K)•Examples: coconut palms, whales, redwoods, man•Includes many of the species in danger of extinction.•energy used to make each individual is high

The Survivorship Curve•Survivorship - the % of an original population that survives to a given age.

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•I - In humans, highest mortality occurs later in life. (K-strategy)•II.- Hydra are likely to die at any age.•III - Oysters produce large numbers of young, few survive. (r-strategy)

•The few that DO survive have a low mortality rate.•The survival curve of hydra is typical of most plants and animals.

The Principle of Competitive Exclusion - if two species are completing with one another for a limited resource, one of the two will be more successful, leading to the eventual disappearance of the other (locally).

The example below shows population growth curves for two species of paramecia raised alone, and then the result of growth in a tank which includes both species.

Predator-Prey Interactions•In nature, prey usually has refuge, which prevent its

local extinction.•Predator and Prey populations, then, become cyclical, and remain balanced.

Fluctuations in predator (wolf) and prey (moose) populations over a 40-year span. Note the effects of declines in the wolf population in the late 1960s and again in the early 1980s on the moose population.

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Predators kill and consume other organisms. Carnivores prey on animals, herbivores consume plants. Predators usually limit the prey population, although in extreme cases they can drive the prey to extinction. There are three major reasons why predators rarely kill and eat all the prey:

1.Prey species often evolve protective mechanisms such as camouflage, poisons, spines, or large size to deter predation.

2.Prey species often have refuges where the predators cannot reach them.3.Often the predator will switch its prey as the prey species becomes lower in abundance: prey

switching.

•A predator that controls the population of one species helps promote ecological diversity (by reducing competitive exclusion).

•Predators that feed on multiple species have a survival advantage.

Populations of Pathogens and Victims•Strains of diseases that are less virulent are selected because they don’t eliminate their host. A

strain that produces sublethal effects will have the opportunity to spread to another host.

Human Populations•The size of the human population will, ultimately, be governed by the environment. (Earth’s

carrying capacity)•Man has the added advantage of using technology to enhance the carrying capacity of the habitats

he chooses to occupy. (Fertilizer, multiple dwellings, transportation, weaponry, clothing manufacture, food distribution, singles ads)•The present human population of Earth is 6.1 billion (2001).•80 million people were added to the world population in 1998.•World population will double in 40 years.

Exponential Growth in the Human Population•It is estimated that human population will level off at 8, 10,or 11 billion people.

Demography•The statistical study of populations.•”demos” = people, “graphos” = measurement•Helps us predict how populations will change in the future.

•Takes into account the age distribution of the population and its changing size through time.•Stable Population - size remains the same through time.

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•Birth + Immigration = Deaths + Emigration•In a stable population, not only does size remain constant, but so does age distribution.

•The characteristics of a population can be illustrated graphically by using a population pyramid - a bar graph using single year or five-year categories.

•Males enumerated to the left, females to the right.•Shows population composition by age and sex.

•The age distribution of human males and females in 1990 in the populations of Mexico, representing rapid growth; and the United States, showing slow growth.

• Age structure refers to the relative proportion of individuals in each age group of a population. Populations with more individuals aged at or before reproductive age have a pyramid-shaped age structure graph, and can expand rapidly as the young mature and breed. Stable populations have relatively the same numbers in each of the age classes.

Introduction of New (Alien, Non-Native) Species

Introduction of exotic or alien non-native species into new areas is perhaps the greatest single factor to affect natural populations. More than 1500 exotic insect species and more than 25 families of alien fish have been introduced into North America. In excess of 3000 plant species have also been introduced. The majority of accidental introductions may fail. However, once an introduced species becomes established, its population growth is explosive. Kudzu, a plant introduced to the American south from Japan, has taken over large areas of the SE US countryside.

KudzuExotic (Alien) Species in Michigan

Zebra MusselsZebra mussels (Dreissena polymorpha) are small, fingernail-sized mussels native to the Caspian Sea region of Asia. They are believed to have been transported to the Great Lakes via ballast water from a transoceanic vessel. The ballast water, taken on in a freshwater European port was subsequently discharged into Lake St. Clair, near Detroit, where the mussel was discovered in 1988. Since that time, they have spread rapidly to all of the Great Lakes and waterways in many states, as well as Ontario and Quebec.  Diving ducks and freshwater drum eat zebra mussels, but will not significantly control them.  Likely means of spread: Microscopic larvae may be carried in livewells or bilgewater. Adults can attach to boats or boating equipment that is in the water.

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Purple Loosestrife

Purple Loosestrife (Lythrum salicaria) is a wetland plant from Europe and Asia. It was introduced into the east coast of North America in the 1800s. First spreading along roads, canals and drainage ditches, then later distributed as an ornamental, this exotic plant is in 40 states and all Canadian border provinces.  The plant can form dense, impenetrable stands that are unsuitable as cover, food or nesting sites for a wide range of native wetland animals, including ducks, geese, rails, bitterns, muskrats, frogs, toads and turtles. Many rare and endangered wetland plants and animals also are at risk.  Purple loosestrife thrives on disturbed, moist soils, often invading after some type of construction activity. Eradicating an established stand is difficult because of an enormous number of seeds in the soil. One adult can disperse 2 million seeds annually. The plant is able to resprout from roots and broken stems that fall to the ground or into the water.  A major reason for purple loosestrife's expansion is a lack of effective predators in North America. Several European insects that only attack purple loosestrife are being tested as a possible long-term biological control in North America.  Likely means of spread: Seeds escape from gardens and nurseries into wetlands, lakes and rivers. Once in aquatic systems, seeds are easily spread by moving water and wetland animals.

The Sea Lamprey

Sea lamprey (Petromyzon marinus) are predaceous, eel-like fish native to the coastal regions of both sides of the Atlantic Ocean. They entered the Great Lakes through the Welland Canal about 1921. They contributed greatly to the decline of whitefish and lake trout in the Great Lakes. Since 1956, the governments of the United States and Canada, working jointly through the Great Lakes Fishery Commission, have implemented a successful sea lamprey control program.  This series of pictures shows a close-up of a lamprey's mouth, lampreys attached to a lake trout, and the damage resulting from a lamprey attack.  

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