Ch 35 Population/ Community Ecology 35. 1 Population Density

Ch 35 Population/ Community Ecology

35.1 Population Density

• Population density is the number of individuals of a particular species per unit area or volume.

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• Examples:

• 35 alligators per square km of a swamp

•  1,000,456 bacteria per cm2 of an agar plate

• 120 earthworms m2 of soil

Population density problems

• On rare occasions you can count all the individuals in

• a population, such as the number of beech trees in a

• forest measuring 50 square kilometers (km2).

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• Population density = Individuals = 1000 trees = 20 trees

• Unit area 50 km2 km2

•  Population density is a helpful measurement for comparing populations in different locations.

35.2 There are limits to a population’s growth

• Exponential growth: growth of a population that multiplies by constant factor

• Limiting factor:condition that restricts a population’s growth, such as space, disease and food availability.

• Carrying capacity: number of organisms in a population that an environment can maintain.

Exponential Growth

• Figure 35-5 This table shows how many bacteria are in a population that doubles every 20 minutes. The graph is another way to show the same data.

CARRYING CAPACITY

• Figure 35-6 Before the early 1900s, hunting kept this population of fur seals below the carrying capacity of the environment. Then, after hunting was reduced, the population grew almost exponentially for two decades. The population began to level off as it reached the carrying capacity.

Growth factors (increase in pop.)

• Growth factors (increase in pop.)

• Immigration: individuals moving into a population
• Births

• Shrinking factors (decrease in pop.)

• Emigration: individuals moving out of a population
• Deaths

Early phase of growth

• Early phase of growth

• High availability of resources

• Little competition

• Little predation

Limits on growth appear

• Limits on growth appear

• Competition for resources
• Predation
• Parasitism
• Illness

35.3 Human Population Growth

• An elephant, cannot survive without other organisms.

• elephant herd of elephants (population) an elephant’s community

• An elephant’s community = gazelles, giraffes, birds, ants, beetles, fungi, bacteria, grasses, trees

• Members of a population compete for limited resources in the environment.

• -Competition within a single species limits the growth of the population.

• Interspecific competition: when two or more species rely on the same limited resource

• (competition between 2 different species)

• example:during times of drought in an African savanna community, grasses may be in short supply, and competition becomes intense.

Competitive Exclusion

• Competitive exclusion: One species succeeding over another, when the growth of both species is limited by the same resource.

• Figure 35-14 Two similar species may each thrive in separate locations, but one may exclude the other when they are placed together. The results of an experiment with two Paramecium species demonstrate this principle of competitive exclusion.

NICHE

• Niche: a unique living arrangement of an organism defined by its living place (habitat), its food sources, the time of day it is most active, and other factors  

• The local loss of a species is likely to occur if 2 species have niches that are very similar

• niches are rarely identical.

• Example: one lizard in a tropical forest feeds on insects in low shrubs, while a similar lizard may eat insects high in the trees.

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Predation

• Predation: an interaction in which one organism eats another.

• The lion attacks and eats an injured zebra or an egret catches and eats a fish.

• Predator: the organism that kills/ eats the prey.

• Prey: the organism that gets eaten.

• eating and avoiding being eaten are important to survival,

• many effective adaptations have evolved in both predators and prey.

Predator/ Prey

• Predator Adaptations

• fast and agile

• camouflage

• teaming up in packs acute senses

• claws, teeth, fangs, and stingers

• Prey Adaptations

• retreat to safe locations

• flee from predators

• camouflage to hide

• "warning coloration" is a caution to predators.

• mimicry -look like organisms that are poisonus or dangerous.

• Plants have poisonous chemicals and structures such as spines and thorns.

Warning Coloration

Monarch w/ warning coloration

Viceroy Butterfly- mimics Monarch

Symbiotic Relationships

• Symbiotic relationship is a close interaction between species in which one of the species lives in or on the other.

• 3 main types of symbiotic relationships: parasitism, mutualism, and commensalism.

• 1.) Parasitism is a relationship in which the parasite obtains its food at the expense of the host.

• Usually the parasite is smaller than the host. (blood-sucking mosquitoes and tapeworms)

Ticks

• Mutualism: both organisms benefit from the symbiotic relationship.

• Your large intestine is inhabited by millions of bacteria.

• The bacteria benefit by having a warm, moist home and food.

• Intestinal bacteria produce vitamin K. Vitamin K is essential for blood clotting.

• Both you and the bacteria benefit from this relationship.

Mutualism

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• Commensalism is a relationship in which one organism benefits, while the other organism is neither harmed nor helped significantly.

• Example:

• A spider crab may place seaweed on its back. The crab benefits by being camouflaged from its predators. The seaweed is not affected.

• commensalism in nature is rare, since most interactions harm one species (parasitism) or help both species (mutualism) to some degree.

Commensalism

35.5 Disturbances are common in communities

Ecological Succession

• Ecological succession. Series of changes in the species of a community, often followed by a disturbance.

• Primary Succession- process by which a community arises in a lifeless area that has no soil

• barren ground lichen/mosses grass shrubs pine trees  hardwood trees

• Examples:

• Forest devastated by a fire, or volcano

• new islands created by erupting volcanoes

• bare rock left behind a retreating glacier.

The establishment and development of an ecosystem in an area that was previously uninhabited

• The establishment and development of an ecosystem in an area that was previously uninhabited

Primary Succession

The island of Surtsey formed by volcanic eruption off of the coast of Iceland during the period from 1963 - 1967

• The island of Surtsey formed by volcanic eruption off of the coast of Iceland during the period from 1963 - 1967

Secondary Succession

• Secondary succession when a disturbance damages an existing community but leaves the soil intact

• Grasses  shrubs trees similar to the original forest.

• Example: when a forested area is cleared for farming and then abandoned.

The recovery of a damaged ecosystem in an area where the soil was left intact

• The recovery of a damaged ecosystem in an area where the soil was left intact

1988 – Devastating forest fires burn much of Yellowstone National Park.

• 1988 – Devastating forest fires burn much of Yellowstone National Park.

1988 – Park map

• 1988 – Park map

• showing areas

• (1.6 million acres)

• burned by the

• series of fires.

1988 fires – The immediate aftermath.

• 1988 fires – The immediate aftermath.

One year after the fires

• One year after the fires

• Note the appearance of fireweed

Ten years after the fires (1998)

• Ten years after the fires (1998)

Twenty years after the fires (2008)

• Twenty years after the fires (2008)

In April, 1986, a nuclear power plant in the former USSR experienced a core meltdown and a catastrophic release of radioactivity into the environment.

• In April, 1986, a nuclear power plant in the former USSR experienced a core meltdown and a catastrophic release of radioactivity into the environment.

Surrounding towns and villages had to be immediately, permanently abandoned.

• Surrounding towns and villages had to be immediately, permanently abandoned.

Secondary succession: trees are colonizing uncultivated fields and meadows

Human Activities and Species Diversity

• humans have had the greatest impact on communities worldwide.

• 60 % Earth's land is used by humans, mostly as cropland or rangeland.

• Human disturbances have a negative effect on species diversity

• Clearing the Land

• for lumber

• land for farming

• Land for building.

• paved over or eventually recolonized by weeds and shrubs, as in abandoned city lots.

Introduced Species

• Introduced species are organisms that humans move from the species' native locations to new geographic areas, either intentionally or accidentally (exotic species).

• Kudzu, a Japanese plant planted widely in the American South (1930s) to help control erosion. especially along irrigation canals. But kudzu soon grew out of control, taking over vast expanses of landscape.

• Some introduced species gain a foothold and may disrupt their new community.

• Some introduced species prey on native species or outcompete native species

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Invasive species

Kudzu vines

Zebra Mussels clogging pipes

35.5 DISTURBANCES

Bioaccumulation: is the process by which substances not readily broken down or excreted can build up and be stored in living tissue (usually in fatty tissue.)

• Bioaccumulation: is the process by which substances not readily broken down or excreted can build up and be stored in living tissue (usually in fatty tissue.)

• Biomagnification: is the process by which substances become more concentrated in the bodies of consumers as one moves up the food chain (trophic levels).

PCBs, or polychlorinated biphenyls, are a group of man-made chemicals.

• PCBs, or polychlorinated biphenyls, are a group of man-made chemicals.

• Introduced in 1929 and widely used in electrical transformers, cosmetics, varnishes, inks, carbonless copy paper, pesticides and for general weatherproofing and fire-resistant coatings to wood and plastic.

• The federal government banned the production of PCBs in 1976

• PCBs can effect the immune system, fertility, child development and possibly increase the risk of certain cancers

DDT is a pesticide that was widely used until being banned in the U.S. in 1972

• DDT is a pesticide that was widely used until being banned in the U.S. in 1972

• DDT accumulates in living tissue, particularly in fat tissue

• High concentrations in some bird species caused failure of eggs by thinning the shells