Env. Science: Ecological Communities
Life requires energy…
At lower levels to organize matter into complex forms — like carbohydrates
To power interactions among species
To power geological forces that shape our planet.
Most simply, energy is defined as the ability to do work.
It is energy that changes the position, composition, or temperature of matter
Energy, like matter, cannot be created or destroyed
This is the first law of Thermodynamics.
The total energy in the universe does not change but energy is not recycled like matter is!
Energy moves in a one-way stream, shaping communities in the process.
Primary producers are known as autotrophs
They capture energy from the sun or chemicals and store it in the bonds of sugars, making it available to the rest of the community
Energy from the sun is captured by plants, algae, or bacteria through photosynthesis
Photosynthesis is the process by which primary producers use sunlight to convert carbon dioxide and water into sugars, releasing oxygen along the way.
6CO2 + 6H2O —> C6H12O6 + 6O2
Not all communities are powered by the sun’s energy,
On the ocean floor, jets of water heated by magma under the Earth’s crust gush into the icy-cold depths.
Deep sea vents are deep enough underwater that they completely lack sunlight.
Primary producers such as bacteria use energy stored in the hydrogen sulfide to convert carbon dioxide and water into sugars in a process called chemosynthesis.
Consumers are known as heterotrophs
They rely on other organisms for energy and nutrients
Herbivores: plant-eaters
Carnivores: meat-eaters
Omnivores: plant- and meant-eaters
Detritivores and decomposers
They use oxygen to break bonds in sugar and release its energy through cellular respiration (primary producers do this too)
Cellular respiration is the process by which organisms use oxygen to release the chemical energy of sugars such as glucose, releasing carbon dioxide and water as a byproduct.
Consumers are also known as heterotrophs
Detritivores such as millipedes and soil insects consume detritus — nonliving organic matter such as leaf litter, and the dead bodies of other community members
Large detritivores, like vultures, are often called scavengers
Decomposers recycle nutrients within the ecosystem by breaking down nonliving organic matter.
These nutrients are then reused by primary producers.
An organism’s rank in a feeding hierarchy is its trophic level.
Primary producers always occupy the first trophic level of any community.
In general, only about 10% of the energy available at any trophic level is passed to the next.
Most of the rest is lost to the environment as heat
A trophic level’s biomass is the mass of living tissue it contains.
In general, there are more organisms and greater biomass at the lower trophic levels than at higher ones.
Food chain: linear series of feeding relationships.
Food web: shows the overlapping and interconnected food chains present in a community.
Keystone species are species that have strong and/or wide-reaching effects on a community.
The removal of a keystone species can significantly alter the structure of the community they live in.
A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity.
Disturbances or changes in the environment can throw a community into equilibrium.
Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession.
Primary succession occurs when there are no traces of the original community remaining, including vegetation and soil.
Pioneer species, such as lichens, are the first to colonize.
The environment changes as new species move in, adding nutrients and generating habitats.
Lichens are a pioneer species that are formed by a mutualistic relationship between algae and fungi.
The algae provide food and energy via photosynthesis.
The fungi take a firm hold on rock and capture the moisture that organisms need to survive.
As the lichens grow, they release acids that break down the rock surface into the beginnings of soil.
Secondary succession occurs when a disturbance dramatically alters a community but does not completely destroy it.
Fores fires, logging, or farming
Occurs much faster than primary succession
Primary aquatic succession occurs when an area fills with water for the first time.
Disturbances such as floods or excess nutrient runoff can lead to it.
A climax community is a stable community that “completes” the succession process.
Ecologists once through succession led to stable climax communities, but today they see communities as temporary, ever-changing associations of species.
Communities are influenced by many factors and constant disturbances.
Invasive species are nonnative organisms that spread widely in a community.
A lack of limiting factors such as predators, parasites, or competitors enables their population to grow.
Not all invasive species are harmful
Although the European honeybee is invasive to North America, they are still beneficial because they pollinate our crops.