2Ecological Succession Learning ObjectivesDescribe how events and processes that occur during ecological succession can change populations and species diversityAfter this lesson you will be able to describe how events and processes that occur during ecological succession can change populations and species diversity.
3Ecological Succession Population – individuals of a given species in a particular areaCommunity – all the different populations in an areaPioneer community – first inhabitants in new communityClimax community – established communityEcological succession – orderly change in makeup of a community over timePioneer ClimaxA population is a group of individuals of a given species in a particular area.A community includes all the different populations in an area. When studying ecological succession, there are two types of communities that need to be considered. A pioneer community includes the first inhabitants of a new community. For example, a pioneer community in a newly formed bog or pond will include algae and certain types of bacteria.A climax community is an established community that undergoes little change. For example, an oak and hickory forest community includes large trees and many different types of animals.Ecological succession is an orderly change in the makeup of a community over time. In succession, a climax community gradually replaces a pioneer community.
4Pioneer vs. Climax Community Pioneer CommunityHarsh environmentBiomass increasingEnergy consumption inefficientSome nutrient lossLow species diversityFluctuations commonClimax CommunityFavorable environmentBiomass stableEnergy consumption efficientNutrient cyclingHigh species diversityFluctuations uncommonA pioneer community usually resides in a harsh environment compared to a climax community’s favorable environment. For instance, a new community succeeding on barren farmland must tolerate dry, unshaded conditions. In contrast, a climax community may contain an abundance of shade trees and moist, rich soil.A pioneer community’s biomass is increasing as new organisms inhabit the area. The biomass of a climax community remains relatively stable since there is little change in the populations within the established community.The energy consumption and nutrient cycling in a pioneer community is inefficient because the food chains are not fully established. The flow of energy of must be complete and efficient for successful nutrient cycling to occur. Climax communities involve efficient energy consumption and nutrient cycling due to the high species diversity.Fluctuations in species and populations are common in pioneer communities, as new “pioneers” move into the community. In contrast, fluctuations are uncommon in climax communities due their state of equilibrium.
5Ecological Succession Ecological succession – land and waterTwo types:Primary succession – newly formed areaSecondary succession – area that has been disturbedHow do events and processes that occur during succession change populations and species diversity?Ecological succession may occur on land and in water. There are two types of ecological succession.Primary succession occurs in newly formed areas where no organisms existed before. For example, a new pond or bog may be created after a period of heavy rain. Also, a new rock formation may be created after a volcanic eruption or shifts in ground structure.Secondary succession occurs in an area that once inhabited organisms, but a disturbance has destroyed the community. Natural disasters and disturbances caused by man can lead to secondary succession.How do events and processes that occur during succession change populations and species diversity? Studying examples of succession will provide answers to this question.
6Primary Succession in Pond Primary succession in newly formed pond:No organismsAlgae and bacteriaHeterotrophic protists and small invertebratesFloating plants (pondweed)Larger plants (cattails) grow around edgesHere are the stages of succession, or change, in a newly formed pond. A flood creates a pond. No organisms are in the pond at first. Pioneer species, such as algae and certain types of bacteria, invade the pond and reproduce. Heterotrophic protists and small invertebrates follow the “pioneers”, because now they have sources of nutrients.Rooted floating plants, such as pondweed, become established. As the pond fills in due to sediment and organic matter, larger plants, such as cattails, grow around edges.
7Primary Succession in Pond Primary succession in newly formed pond:Larger animalsBecomes marsh, fills inShrubs and treesResults:Pioneer ClimaxAquatic TerrestrialIncreased species diversityComplex food chainsLarger animals, such as water birds and amphibians, move into community because of the favorable changes. Increased plant diversity leads to increased animal diversity due to the vast array of food sources. The pond community may become a marsh community with the increase of plant populations. The marsh may eventually fill in completely, allowing shrubs and trees to grow.The results of primary succession include the establishment of a climax community from a pioneer community. In this case, a terrestrial ecosystem replaced an aquatic one. This new terrestrial ecosystem has increased species diversity and complex food chains.
8Primary Succession on Rocks Cooled lava rocks form after volcanic eruptionLichens and mosses appear, dissolve rock, form soilDead lichens add organic matterSmall animalsThese are the stages of primary succession on cooled lava rocks that formed after a volcanic eruption. Lichens and mosses are the first pioneer species to colonize rocks. Lichens excrete acids that dissolve rock. This dissolved rock forms soil. Dead lichens add organic matter to the developing soil. This richer soil creates a favorable environment for small animals, such as insects.
9Primary Succession on Rocks More diverse plantsMore diverse, larger animalsResults:Pioneer ClimaxBarren rock Terrestrial ecosystemMore diverse species and populationsAs the nutrient content of soil increases, more plants grow. The soil can now sustain plants with large root systems. More diverse plant populations result in more diverse animal populations due to the increased variety of food sources.The results of this primary succession on rocks include the establishment of a climax community from a pioneer community. A barren rock now becomes a terrestrial ecosystem that can sustain diverse species and populations of organisms.
10Secondary SuccessionSecondary succession – sequence of changes after a climax community has been destroyedNatural disastersForest fireFloodSecondary succession occurs after a climax community has been destroyed. Natural disasters, such as forest fires and floods, can destroy a community. The picture shows a pine forest community immediately after a forest fire, then a few months later. Weeds have begun to establish themselves as a pioneer species. Succession has begun.
11Secondary SuccessionSecondary succession – sequence of changes after a climax community has been destroyedDestruction by manClearing land for construction or harvestAbandoned farmlandSecondary succession can also occur after a community has been destroyed by man. The clearing of land for construction or harvest and abandoned farmland can lead to secondary succession.
12Secondary Succession on Farmland Secondary succession on abandoned farmland:Soil is sunlit and dryWeeds are pioneers speciesHere are the stages of secondary succession on abandoned farmland. This photo shows land that was once a forest, but was cleared for farmland. Now the farmland has been abandoned. Due to the lack of shade, the soil in the abandoned field was sunlit and dry.Weeds, such as crabgrass, can grow in bright, dry conditions. These weeds are the pioneer species of this community.
13Secondary Succession on Farmland Secondary succession on abandoned farmland:Weeds die, adding nutrients to soilMore plant speciesSoil shaded by grasses and shrubsPine seedlingsPine forest community (climax)Results:Abandoned farmland Pine forestMore diverse species and populationsGenerations of weeds eventually died, adding nutrients to soil. The ground can now support other species of plants, such as grasses and shrubs. These new plant species now shade the soil. This shaded environment is favorable for pine seedlings to sprout up in the field. After about 50 years, a pine forest community now flourishes as the climax community.The results of this secondary succession on abandoned farmland include more diverse species and populations due to the favorable habitat of the climax community.
14Ecological Succession Summary of Ecological SuccessionSpecies, populations, and communities change over timeUnfavorable environment Favorable environmentFew food sources Many food sourcesFew species Many species Diverse populationsPioneer community Climax communityHere is a summary of ecological succession. Just as individual organisms grow and change with time, so do species, populations, and communities. Populations in a particular area change the environment by their very presence. A harsh, unfavorable environment may now become a favorable environment to more populations.Due to the increasingly favorable environment, there is an increase in species diversity which leads to an increase in food sources. This results in nutrient cycling through complex food chains involving many different populations of organisms. The once harsh, pioneer community becomes a thriving climax community.
15Ecological Succession Learning ObjectivesDescribe how events and processes that occur during ecological succession can change populations and species diversityYou should now be able to describe how events and processes that occur during ecological succession can change populations and species diversity.