Community Interactions What are keystone species? A keystone species is one which has a large impact on its ecosystem. Keystone species plays a major role in determining community structure. Removal of the keystone species dramatically alters the community. For example, the keystone role played by the lobster in the east cost of Canada. Overfishing of lobsters allowed sea urchins, a prey of lobster, to increase in numbers. The population explosion of sea urchins nearly eliminated certain types of algae on which the urchins feed, leaving large expanses (areas) of bare (exposed) rock where a diverse community once existed. 1

Community Interactions How does a community change over time? Mature communities do not spring (start) fully formed from bare rock or naked soil, but rather emerge in stages over a long period. This gradual change in a community structure and its nonliving environment over time is called succession. Succession takes two major forms: primary succession secondary succession 2

Community Interactions How does a community change over time? Primary succession Primary succession is the colonization of an area that has not been previously occupied by an ecological community. It is the generation of a community from scratch; a process that requires thousands or even ten thousands of years. Fore example, a community colonizes bare rock, sand and lava flows. 3 Pioneer lichens colonize bare rock Pioneer ferns colonize hardened lava

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 1.The rock weathers forming cracks and releasing nutrients such as minerals. 2.Lichens (pioneer species) begin to settle (colonize); they manufacture food by photosynthesis. Acids from the lichens begin breaking the rock into small particles. These particles mix with the remains of dead lichens to start forming soil. 3.As some lichens die, the decomposers arrive adding nutrients. 4

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 4.Drought-resistant, sun-loving simple plants like mosses begin growing in the cracks. The mosses form a dense mat that traps dust and moisture, and thus adding to the soil formation. 5.The soil gets enriched as mosses die. 5

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 6.Within the mat, seeds of larger plants, herbs and weeds, such as bluebell and yarrow, germinate. 7.Latter, these plants die and their bodies contribute to new soil formation. 6

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 8.Woody shrubs, such as blueberry and juniper grow in the newly formed soil. 7

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 9.Ultimately, trees such as jack pine and aspen thrive. 8

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 10.Now larger trees, a climax community, can grow: oak, balsam fir, walnut and maple 11.After a thousand years or more, a tall climax forest thrives on what was once bare rock. 9

Community Interactions How does a community change over time? Stages of primary succession (succession with bare rock) 12.What was once bare rock now supports a variety of life 10

Community Interactions How does a community change over time? A summary of changes that occur during primary succession 11

Community Interactions How does a community change over time? Secondary succession Secondary succession is the development of a new community after an existing ecosystem is disturbed. The disturbance might be a forest fire or abandonment farm fields Because the soil which already contains the seeds is present, Secondary succession is faster than primary succession. 12 Boreal pine forest after fire

Community Interactions How does a community change over time? Secondary succession Secondary succession takes place following a major disturbance, such as a fire or flood. Farmland that has been abandoned also can undergo secondary succession. The stages of secondary succession are similar to those of primary succession with one important difference: primary succession always begins on a barren surface, while secondary succession begins in an area that already has soil. 13 Boreal pine forest after fire

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 1. A stable deciduous forest community. 14

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 2.A disturbance, such as a wild fire, destroys the forest. 3. The fire burns the forest to the ground. 15

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 4.The fire leaves behind empty, but not destroyed, soil. 5. Annual plants (species that live for a single growing season), like Grasses and other herbaceous plants (pioneer species) grow in the rich soil already present. 16

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 6.Small bushes and trees begin to colonize the area. 17

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 7.Longer-lived perennial plants like tulip poplar and pine grow and dominate for few decades. 18

Community Interactions How does a community change over time? Stages of secondary succession (succession after forest fire) 8.Eventually, shade-tolerant seedlings of slow-growing and taller trees, such as oak, dominate. 9. The ecosystem is now back to a similar state from which it began. 19

Community Interactions How does a community change over time? A summary of changes that occur during secondary succession 20

Community Interactions How does a community change over time? A summary of changes that occur during secondary succession 21 Succession of plant species on abandoned fields in North Carolina. Pioneer species consist of a variety of annual plants. This successional stage is then followed by communities of perennials and grasses, shrubs, softwood trees and shrubs, and finally hardwood trees and shrubs. This succession takes about 120 years to go from the pioneer stage to the climax community.Pioneer speciespioneerclimax

Community Interactions How does a community change over time? A summary of changes that occur during secondary succession 22

Climax community  The final and stable community (stable groups of plants and animals) that is the end result of the succession process.  Climax community does not always mean big trees, for example:  Grasses in prairies  Cacti in deserts Community interactions

Primary successionSecondary succession Begins with no soilBegins with soil Pioneer organisms (lichens, mosses) Pioneer organisms (annual plants and grasses) Caused by events like lava flows Caused by events like forest fires Takes long timeTakes shorter time to grow back

Community interactions Climax Community: A community that no longer undergoes changes in structure or species composition due to succession. Annual Plant: Plant species that completes its life in one growing season. Shrub: A woody plant species that is smaller than a tree. Shrubs usually do not have a trunk. Perennial Plant: Plant species that lives for more than two years.