Patterns In Communities

Ecological Succession• If you leave a grassy field

to itself, what will happen over a period of time?

• The overall species in the field will change

• Grasses will give way to small bushes and small trees

• Small bushes and small trees give way to larger trees

Ecological Succession

• The progression of grasslands to forests is called Ecological Succession– It can also be called

natural succession• Succession is made of

two different types of species

Ecological Succession

• Pioneer Species – These are species that are fast to grow and often take over a new environment

• Colonizers – These are species that are longer lived and are general more advanced

Primary Succession

• If a new environment opens pioneer species are the first to grow

• They can grow in almost any form of environment

• Being fast growing and producing lots of offspring that can be spread around allows for rapid expansion

Primary Succession

• Pioneer species create new and more fertile soil

• They can break apart rocks and hard surfaces

• After they die, they return vital nutrients to the soil that allow more complex organisms to grow

Primary Succession

• The process of going from no or limited soil to rich soil is called primary succession

• This process can take a small amount of time or a large amount of time

• It all depends on what surface the pioneers start on

http://www.youtube.com/watch?v=zv2JNaqnYxU&feature=related

Secondary Succession

• Once the conditions in an area allow for more complex organisms, colonizers will start to grow

• These take many more years to start growing and take many more years to actually take hold

Secondary Succession

• The trees that make up secondary succession will out compete the pioneer species

• This means that you will find many more colonizers in an established secondary succession forest

Secondary Succession• When plants reach the

point where they are as complex and diverse as the environment will allow them, they will stay the same

• Succession will no longer continue

• A climax community is when succession reaches a predictable and stable endpoint

Video

• http://www.youtube.com/watch?v=A62au7Avq1E

Aquatic Succession

• Succession can happen in aquatic environments

• Lakes or ponds are generally sloped on the sides and deep in the center

• Through erosion over time, soil will start to move into the pond

Aquatic Succession

• This will slowly start to fill the pond

• As the sides of the pond become more shallow, terrestrial plants can start to grow

• Eventually the lake will slowly fill

• The climax community would be a bog swamp

Community Stability and Species Richness

• Species richness can be changed by the biotic and abiotic changes to the ecosystem as well

• A change in the number of organisms, resources or ability to get to resources is called a disturbance

Community Stability and Species Richness

• Disturbances can be biotic or abiotic

• Abiotic disturbances might be storms, floods, fires, eruptions or drought

• Biotic disturbances could be a plague, famine, infestation of parasites or new species introduced

Community Stability and Species Richness

• Disturbances happen to all ecosystems and in general have a negative effect on species richness

• They decrease the overall populations of species and can wipe out the populations of other species

Community Stability and Species Richness

• However there are many times when a disturbance can increase species richness over time

• When the ecosystem starts to recover it has new habitats that can bring in new species

Community Stability and Species Richness

• http://www.youtube.com/watch?v=qIxyUcb2wqI

Species Richness

• Since communities based are the interactions between species, it is important to measure that quality

• Species richness is the number of species in the community

Species Richness

• Species richness is a quality that is good for an overall community

• With more species in the community there are larger possible food webs

• With more species and interactions, the ecosystem can survive larger disturbances

Latitude and Species Richness

• Species richness can vary across different ecosystems and biomes

• In general species richness will increase the closer that it is to the equator

• In general species richness will decrease the farther from the equator an ecosystem is

Latitude and Species Richness• The overall species

richness depends on the latitude for several reasons

• Ecosystems that are closer to the equator have more heat energy

• Along with more heat energy generally comes an increased section of the water cycle

Latitude and Species Richness• Another reason why

latitude contributes to species richness is the plant life

• Plants around the equator perform photosynthesis year round

• This year round photosynthesis allows a larger range of species to survive

Habitat Size and Species Richness

• The size of the overall habitat can contribute to species richness

• In general there is more species richness in larger habitats

• In general there is less species richness in smaller habitats

Habitat Size and Species Richness

• This is called the species-area effect

• This is because the more area there is for species to grow, the more species you will find in that habitat

• In general there is a large amount of habitat size on continents

Habitat Size and Species Richness• The size of a habitat often

affects the number of species on islands

• On islands there is limited space and there are often different ecosystems that interact

• This reduces the size of habitats and the number of organisms and species in those habitats