topic 2.5: Zonation, succession and change in ecosystems
http://www.mesa.edu.au/friends/seashores/zonation.html
Subtopic 2.5 delves into ecological succession, the process by which ecosystems develop and change over time, progressing through various stages until reaching a stable climax community. This natural progression involves both primary and secondary succession, each starting from different initial conditions but following similar pathways through seral communities.
Ecological succession is a fundamental concept in ecology, illustrating how ecosystems evolve and mature. Primary succession begins on newly formed or exposed substrates without pre-existing soil, such as volcanic rock or glacial moraines, and involves pioneer species initiating soil formation. Secondary succession occurs on pre-existing soil following disturbances that remove previous vegetation, such as fires or agricultural abandonment. Both types of succession progress through seral communities, with each stage modifying the environment to support subsequent species. The process culminates in a climax community, a stable and diverse ecosystem in equilibrium with the local environment. Understanding these processes is crucial for ecological restoration and management, providing insights into how ecosystems recover and develop resilience.
This unit is a minimum of 4.5 hours
Ecological succession is a fundamental concept in ecology, illustrating how ecosystems evolve and mature. Primary succession begins on newly formed or exposed substrates without pre-existing soil, such as volcanic rock or glacial moraines, and involves pioneer species initiating soil formation. Secondary succession occurs on pre-existing soil following disturbances that remove previous vegetation, such as fires or agricultural abandonment. Both types of succession progress through seral communities, with each stage modifying the environment to support subsequent species. The process culminates in a climax community, a stable and diverse ecosystem in equilibrium with the local environment. Understanding these processes is crucial for ecological restoration and management, providing insights into how ecosystems recover and develop resilience.
This unit is a minimum of 4.5 hours
Guiding Question
- How do ecological systems change over time and over space?
- How do abiotic and biotic factors influence the process of zonation in an ecosystem?
- What are the stages of ecological succession, and how do pioneer species contribute to ecosystem development?
- How do human activities impact the natural processes of zonation and succession in various ecosystems?
Understanding:
zonation
2.5.1 Zonation refers to changes in community along an environmental gradient.
- Define and give an example of zonation.
Zonation refers to changes in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore (coverage by water).
The distinct vertical layers experience particular abiotic conditions. This is particularly clear in the distribution of plants and animals on a rocky seashore, where different species inhabit a series of horizontal strips or belts of the shore, approximately parallel to the water's edge. In many places the strips (zones) are sharply bounded by the differently coloured seaweeds that populate them.
The division of vegetation in relation to a successional sequence (e.g. in sand-dunes), implying that spatial zonation may correspond to temporal processes.
The distinct vertical layers experience particular abiotic conditions. This is particularly clear in the distribution of plants and animals on a rocky seashore, where different species inhabit a series of horizontal strips or belts of the shore, approximately parallel to the water's edge. In many places the strips (zones) are sharply bounded by the differently coloured seaweeds that populate them.
The division of vegetation in relation to a successional sequence (e.g. in sand-dunes), implying that spatial zonation may correspond to temporal processes.
2.5.2 Transects can be used to measure biotic and abiotic factors along an environmental gradient in order to determine the variables that affect the distribution of species.
- Describe the difference between line transects and belt transects
- Discuss how environmental gradients can affect the distribution of species along a transect.
Transects are valuable tools in ecological studies for measuring biotic (living) and abiotic (non-living) factors along an environmental gradient. By systematically sampling along these transects, scientists can identify the variables that influence the distribution of species within different habitats.
A transect is a straight line or narrow section through a natural feature or across an environmental gradient, along which observations and measurements are made.
Types of Transects:
Purpose of Using Transects
A transect is a straight line or narrow section through a natural feature or across an environmental gradient, along which observations and measurements are made.
Types of Transects:
- Line Transects: A line is laid out, and observations are made at specific intervals along the line.
- Belt Transects: A strip of habitat is marked, and all organisms within the strip are recorded, along with abiotic factors.
Purpose of Using Transects
- Environmental Gradients: Environmental gradients are changes in abiotic factors like temperature, light, moisture, or soil type over a certain distance. These gradients can significantly affect the distribution of species.
- Data Collection: Transects allow researchers to collect data systematically on both biotic and abiotic factors, providing a comprehensive view of how these factors interact.
Kite Diagram
Kite diagrams are a chart that shows the number of animals (or percentage cover for plants) against distance along a transect. The distribution of organisms in a habitat is affected by the presence of other living organisms, such as herbivores or predators that might eat them. It is also affected by abiotic factors (physical factors) such as availability of light or water. The width of the “kite” represents the number of species.
The kite diagram is frequently used to show zonation along a transect. A gradual change in the distribution of species across a habitat is called zonation. It can happen because of a gradual change in an abiotic factor. A transect is line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground. The number of organisms of each species can be observed and recorded at regular intervals along the transect.
Kite diagrams are a chart that shows the number of animals (or percentage cover for plants) against distance along a transect. The distribution of organisms in a habitat is affected by the presence of other living organisms, such as herbivores or predators that might eat them. It is also affected by abiotic factors (physical factors) such as availability of light or water. The width of the “kite” represents the number of species.
The kite diagram is frequently used to show zonation along a transect. A gradual change in the distribution of species across a habitat is called zonation. It can happen because of a gradual change in an abiotic factor. A transect is line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground. The number of organisms of each species can be observed and recorded at regular intervals along the transect.
Application of skills: Investigate zonation along an environmental gradient using a transect sampling technique and a range of relevant abiotic measurements.
Create kite diagrams to show distribution.
Create kite diagrams to show distribution.
succession
2.5.3 Succession is the replacement of one community by another in an area over time due to changes in biotic and abiotic variables..
- Define and give an example of succession.
- Distinguish between primary and secondary succession
Succession is a directional non-seasonal cumulative change in the types of plant species that occupy a given area through time. It involves the processes of colonization, establishment, and extinction which act on the participating plant species. Most successions contain a number of stages that can be recognized by the collection of species that dominate at that point in the succession. Succession begin when an area is made partially or completely devoid of vegetation because of a disturbance. Some common mechanisms of disturbance are fires, wind storms, volcanic eruptions, logging, climate change, severe flooding, disease, and pest infestation. Succession stops when species composition changes no longer occur with time, and this community is said to be a climax community.
Examples of succession:
Examples of succession:
- Hydrosere: Succession in a body of freshwater. In this process small lakes may disappear and be replaced by the plant communities.
- Halosere: Succession in salt water marshes.
- Psammosere: Succession along sand dunes. This stabilizes the dunes and stops them shifting.
- Lithosere: Succession starting from bare rock. This is seen most often on lava flows.
- Xerosere: Succession in dry areas.
- The species living in a particular place gradually change over time as does the physical and chemical environment within that area.
- Succession takes place because through the processes of living, growing and reproducing, organisms interact with and affect the environment within an area, gradually changing it.
- Each species is adapted to thrive and compete best against other species under a very specific set of environmental conditions. If these conditions change, then the existing species will be outcompeted by a different set of species which are better adapted to the new conditions.
- The most often quoted examples of succession deal with plant succession. It is worth remembering that as plant communities change, so will the associated micro-organism, fungus and animal species. Succession involves the whole community, not just the plants.
- Change in the plant species present in an area is one of the driving forces behind changes in animal species. This is because each plant species will have associated animal species which feed on it. The presence of these herbivore species will then dictate which particular carnivores are present.
- The structure or 'architecture' of the plant communities will also influence the animal species which can live in the microhabitats provided by the plants.
- Changes in plant species also alter the fungal species present because many fungi are associated with particular plants.
- Succession is directional. Different stages in a particular habitat succession can usually be accurately predicted.
- These stages, characterised by the presence of different communities, are known as 'seres'.
- Communities change gradually from one sere to another. The seres are not totally distinct from each other and one will tend to merge gradually into another, finally ending up with a 'climax' community.
- Succession will not go any further than the climax community. This is the final stage.
This does not however, imply that there will be no further change. When large organisms in the climax community, such as trees, die and fall down, then new openings are created in which secondary succession will occur.
- Many thousands of different species might be involved in the community changes taking place over the course of a succession. For example, in the succession from freshwater to climax woodland.
- The actual species involved in a succession in a particular area are controlled by such factors as the geology and history of the area, the climate, microclimate, weather, soil type and other environmental factors.
2.5.4 Each seral community (sere) in a succession causes changes in environmental conditions that allow the next community to replace it through competition until a stable climax community is reached.
- Define a seral community and explain its role in ecological succession.
Ecological succession is the process by which an ecological community undergoes gradual changes over time, ultimately leading to the establishment of a stable climax community. During succession, each seral community, or sere, modifies the environment in ways that facilitate the establishment of subsequent communities. This sequence of changes continues until the ecosystem reaches stability.
A seral community, or sere, is a stage in the succession process, characterized by a specific group of plants and animals that dominate the ecosystem temporarily.
Each seral community alters the environment in ways that make it more suitable for the next community. These changes can include modifications to soil composition, light availability, and microclimate conditions.
Stages of Succession
A seral community, or sere, is a stage in the succession process, characterized by a specific group of plants and animals that dominate the ecosystem temporarily.
Each seral community alters the environment in ways that make it more suitable for the next community. These changes can include modifications to soil composition, light availability, and microclimate conditions.
Stages of Succession
- Primary Succession:
- Initial Stage: Begins on bare rock or other surfaces without soil, such as after a volcanic eruption or glacier retreat.
- Pioneer Species: The first organisms to colonize, typically lichens and mosses, which start soil formation by breaking down rock and accumulating organic matter.
- Secondary Succession:
- Initial Stage: Occurs in areas where a disturbance has removed the existing vegetation but left the soil intact, such as after a fire, flood, or human activity.
- Pioneer Species: Early colonizers like grasses and weeds quickly establish, stabilizing the soil and adding organic matter.
2.5.5 Primary successions happen on newly formed substratum where there is no soil or preexisting community, such as rock newly formed by volcanism, moraines revealed by retreating glaciers, wind-blown sand or waterborne silt.
- Define primary succession and explain its importance in ecosystem development.
- Identify and describe the role of pioneer species in primary succession.
- Explain how soil formation occurs during the early stages of primary succession
Primary succession is the ecological process by which life colonizes an area that has not previously supported a community, such as newly formed volcanic rock, glacial moraines, wind-blown sand, or waterborne silt. This process involves a series of seral communities or stages, starting with pioneer species and eventually leading to a climax community.
Stages of Primary Succession
Stages of Primary Succession
- Pioneer Community:
- Pioneer Species: The first organisms to colonize newly formed substratum are typically lichens and mosses. These species are well-adapted to harsh conditions and can grow directly on bare rock or sand.
- Soil Formation: Lichens and mosses begin the process of soil formation by breaking down the rock through physical and chemical weathering. As they die and decompose, they add organic matter to the developing soil.
- Seral Communities or Stages:
- Early Seral Stages: As the soil layer develops, it becomes suitable for grasses and herbaceous plants. These plants further stabilize the soil and contribute to its enrichment by adding organic matter and nutrients.
- Intermediate Seral Stages: With improved soil quality, shrubs and small trees begin to colonize the area. These plants provide more structure to the ecosystem and create habitats for various animal species.
- Climax Community:
- Development: Over time, the ecosystem continues to evolve, and more complex plant species establish themselves. This leads to the development of a climax community, characterized by a diverse array of plant and animal species in a stable, self-sustaining ecosystem.
- Stability: The climax community is relatively stable, with efficient nutrient cycling and energy flow, and remains in equilibrium with the environmental conditions of the area.
Bare, inorganic surface → stage 1 colonisation → stage 2 establishment → stage 3 competition → stage 4 stabilisation → climax community
https://news.uchicago.edu/explainer/what-is-ecological-succession
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Case Study: Primary Succession: Surtsey Island
https://www.cruisemapper.com/ports/surtsey-island-port-2457
https://grapevine.is/news/2019/07/22/new-research-island-of-surtsey-blossoming-with-life/
Formation of Surtsey:
- Origin: Surtsey is a volcanic island that emerged from the ocean off the coast of Iceland in 1963 due to a volcanic eruption.
- Initial State: When the island first formed, it consisted of bare volcanic rock with no soil or existing community.
- Pioneer Species: The first organisms to colonize Surtsey were lichens and mosses. These species are well-adapted to harsh conditions and can grow directly on bare rock.
- Soil Formation: Lichens and mosses began the process of soil formation by breaking down the volcanic rock through physical and chemical weathering. As they died and decomposed, they added organic matter to the developing soil.
- Early Seral Stages: As the soil layer developed, it became suitable for grasses and herbaceous plants. These plants further stabilized the soil and contributed to its enrichment by adding organic matter and nutrients.
- Intermediate Seral Stages: Shrubs and small trees began to colonize the island as the soil depth and quality improved. These plants provided more structure to the ecosystem and created habitats for various animal species.
- Development: Over time, Surtsey's ecosystem continued to evolve, and more complex plant species established themselves. This led to the development of a climax community, characterized by a diverse array of plant and animal species in a stable, self-sustaining ecosystem.
- Stability: The climax community on Surtsey is now relatively stable, with efficient nutrient cycling and energy flow. It remains in equilibrium with the environmental conditions on the island.
2.5.6 Secondary successions happen on bare soil where there has been a pre-existing community, such as a field where agriculture has ceased or a forest after an intense firestorm.
- Define secondary succession
- Describe the role of pioneer species in secondary succession.
- Discuss how soil quality influences the progression of secondary succession.
Secondary succession is the ecological process that occurs on bare soil where a pre-existing community has been disturbed or removed but the soil remains intact. This process is common in environments such as abandoned agricultural fields, areas cleared by logging, or forests after intense firestorms. Unlike primary succession, which starts from bare rock or newly formed substrates, secondary succession starts with existing soil that already contains seeds, roots, and organic matter.
Stages of Secondary Succession
Initial Disturbance:
Intermediate Stages:
Late Stages and Climax Community:
Stages of Secondary Succession
Initial Disturbance:
- Pre-existing Community: Prior to the disturbance, the area would have supported a mature ecosystem with established plants and animals.
- Disturbance: The disturbance event (e.g., agricultural abandonment, logging, fire) removes the existing vegetation but leaves the soil and its seed bank intact.
- Pioneer Species: The first colonizers in secondary succession are typically fast-growing herbaceous plants and grasses. These species quickly occupy the bare soil, stabilize it, and prevent erosion.
- Soil Stabilization: Pioneer species improve soil fertility through organic matter accumulation and nitrogen fixation.
Intermediate Stages:
- Shrubs and Perennial Plants: As soil conditions improve, shrubs and other perennial plants establish, gradually outcompeting the pioneer species.
- Increased Biodiversity: The establishment of shrubs and perennials creates a more complex habitat, supporting a wider range of insects, birds, and other wildlife.
Late Stages and Climax Community:
- Tree Establishment: Over time, tree species begin to dominate the area, leading to the development of a forested ecosystem.
- Climax Community: The final stage of succession is a stable, mature forest or woodland, characterized by high biodiversity, stable structure, and efficient nutrient cycling.
https://news.uchicago.edu/explainer/what-is-ecological-succession
Case Study: Secondary Succession After the 2016 Fort McMurray Wildfire in Alberta, Canada
https://edmonton.ctvnews.ca/drones-interfere-with-wildfire-operations-near-fort-mcmurray-saprae-creek-estates-under-evacuation-alert-1.6856128
In May 2016, a massive wildfire swept through Fort McMurray in Alberta, Canada, burning approximately 590,000 hectares and forcing the evacuation of nearly 90,000 residents. The fire caused significant damage to the boreal forest ecosystem, offering a contemporary example to study secondary succession.
Pre-Disturbance Conditions:
Initial Disturbance:
Early Stages of Secondary Succession:
Intermediate Stages:
Late Stages and Climax Community:
Pre-Disturbance Conditions:
- Ecosystem: The region primarily consisted of boreal forest, dominated by species such as black spruce, white spruce, jack pine, and trembling aspen.
- Soil: The soil was nutrient-rich with a well-developed organic layer and a diverse seed bank.
Initial Disturbance:
- The intense fire removed large areas of mature vegetation but left the soil largely intact. The fire also created openings in the forest canopy, allowing sunlight to penetrate the forest floor.
Early Stages of Secondary Succession:
- Pioneer Species: Within a year of the wildfire, early colonizers such as fireweed, grasses, and jack pine seedlings began to establish. These species are adapted to fire and can rapidly occupy disturbed areas.
- Soil Stabilization: These pioneer species helped stabilize the soil, preventing erosion, and contributed organic matter to the soil as they grew and decomposed.
Intermediate Stages:
- Shrubs and Perennial Plants: Over the next few years, shrubs like willow and perennial herbs started to establish, benefiting from improved soil conditions and reduced competition.
- Increased Biodiversity: The increasing diversity of plant species provided habitats for various insects, birds, and small mammals, enhancing the overall biodiversity of the recovering ecosystem.
Late Stages and Climax Community:
- Tree Establishment: By the second decade after the fire, tree species such as black spruce, white spruce, and aspen are expected to re-establish dominance, leading to the reformation of the boreal forest.
- Climax Community: The climax community will likely resemble the pre-fire boreal forest, with a complex structure, high biodiversity, and stable ecological functions.
2.5.7 Energy flow, productivity, species diversity, soil depth and nutrient cycling change over time during succession.
- Explain how the patterns of energy flow, productivity, diversity, and mineral cycling change during succession.
image from en.wikipedia.org
Ecological succession involves a series of progressive changes in an ecosystem over time. As succession progresses, several key ecological processes and characteristics change, including energy flow, productivity, species diversity, soil depth, and nutrient cycling. These changes contribute to the development of a stable and mature ecosystem.
Energy Flow
Productivity
Species Diversity
Soil Depth
Nutrient Cycling
Energy Flow
- Early Succession:
- In the initial stages, pioneer species have high rates of photosynthesis but low biomass, leading to limited energy storage within the ecosystem.
- Energy flow is relatively straightforward, with few trophic levels and simple food webs.
- Later Succession:
- Plant biomass increases, more energy is stored in the ecosystem.
- The establishment of a variety of plants and animals leads to more complex food webs and multiple trophic levels, enhancing energy transfer and stability.
Productivity
- Early Succession:
- Pioneer species often exhibit rapid growth and high primary productivity due to ample light and nutrients.
- Initial stages have low secondary productivity because of the limited presence of herbivores and predators.
- Later Succession:
- As the ecosystem matures, primary productivity stabilizes and may decrease slightly as competition for light and nutrients increases.
- With more complex food webs and higher species diversity, secondary productivity increases.
Species Diversity
- Early Succession:
- Initial colonization by pioneer species leads to low species diversity.
- Species that are well-adapted to colonizing disturbed areas dominate.
- Later Succession:
- As the ecosystem develops, species diversity increases, reaching its peak in the mature stages.
- Climax communities are characterized by high biodiversity and stable species compositions.
Soil Depth
- Early Succession:
- Initial stages involve the formation of shallow soil as pioneer species break down parent material and contribute organic matter.
- Soil is initially poor in structure and nutrient content.
- Later Succession:
- Over time, soil depth increases due to the accumulation of organic matter and the activity of decomposers.
- Soil becomes richer in nutrients and better structured, supporting a wider variety of plant species.
Nutrient Cycling
- Early Succession:
- Nutrient cycling is relatively simple and rapid, with few species involved in the process.
- Nutrients are readily available due to the low biomass and high rates of decomposition.
- Later Succession:
- Nutrient cycling becomes more complex, involving multiple species and intricate interactions.
- Mature ecosystems retain nutrients more effectively, reducing losses and enhancing soil fertility.
- Nutrient cycling becomes more complex, involving multiple species and intricate interactions.
Consider data in tables or figures related to succession and the reasons for changes in these factors.
Understanding ecological succession involves analyzing changes in various factors such as energy flow, productivity, species diversity, soil depth, and nutrient cycling. These changes can be effectively illustrated through data presented in tables or figures. Here, we outline how to interpret such data and the reasons behind these ecological changes during succession.
Understanding ecological succession involves analyzing changes in various factors such as energy flow, productivity, species diversity, soil depth, and nutrient cycling. These changes can be effectively illustrated through data presented in tables or figures. Here, we outline how to interpret such data and the reasons behind these ecological changes during succession.
Reasons for Changes:
- Early Succession: High energy input from pioneer species' rapid growth but low energy storage due to limited biomass.
- Mid Succession: Increased energy input and storage as more plants and herbivores establish, creating more complex food webs.
- Late Succession: Energy input stabilizes; increased energy storage in biomass as mature plants dominate.
- Climax Community: Energy input and storage reach equilibrium; efficient energy use with minimal losses.
2.5.8 An ecosystem’s capacity to tolerate disturbances and maintain equilibrium depends on its diversity and resilience.
- Define ecosystem resilience
- Explain how the resilience of the ecosystem can impact its response to change
- Explain what is meant by ecosystem resilience.
- Explain the relationship between species diversity and ecosystem stability.
- Describe how primary and secondary succession contribute to increasing ecosystem diversity and resilience.
image from femsre.oxfordjournals.org
An ecosystem's capacity to tolerate disturbances and maintain equilibrium is fundamentally linked to its diversity and resilience. These attributes are critical for the long-term sustainability of ecosystems, allowing them to recover from disruptions and continue functioning effectively. Understanding the connections between ecosystem resilience, stability, succession, diversity, and human activity is essential for ecological research and conservation.
Ecosystem Resilience and Stability
Role of Diversity in Ecosystem Resilience and Stability
Succession and Its Impact on Diversity and Resilience
Human Activity and Its Effects on Ecosystem Resilience and Stability
Ecosystem Resilience and Stability
- Resilience: Ecosystem resilience is the ability of an ecosystem to absorb disturbances, recover from them, and return to its original state.
- Resilient ecosystems can withstand and adapt to changes, minimizing long-term damage and maintaining ecological functions.
- Stability: Ecosystem stability refers to the ability of an ecosystem to remain relatively unchanged in the face of disturbances.
- Stability includes resistance (the ability to withstand disturbances) and resilience (the ability to recover from disturbances).
Role of Diversity in Ecosystem Resilience and Stability
- Species Diversity:
- High species diversity means more functional redundancy, where multiple species perform similar ecological roles. This redundancy allows ecosystems to maintain functions even if some species are affected by disturbances.
- Diverse ecosystems are less likely to experience drastic changes in structure and function because different species respond to disturbances in varied ways, balancing the overall impact.
- Functional Diversity:
- Ecosystems with a wide range of functional traits among species are more adaptable to changes. Functional diversity ensures that essential processes, such as nutrient cycling and energy flow, are maintained under different conditions.
- Functional diversity provides a buffer against disturbances by spreading risk across multiple species and functions.
Succession and Its Impact on Diversity and Resilience
- Primary and Secondary Succession:
- Succession leads to the gradual buildup of species diversity as pioneer species are replaced by more complex communities. This increase in diversity enhances resilience and stability.
- Each stage of succession contributes to soil development, nutrient cycling, and habitat complexity, further supporting diverse species and functional roles.
- Climax Community:
- The climax community represents a mature and stable ecosystem with high biodiversity and well-established ecological functions.
- Climax communities are highly resilient, capable of recovering from disturbances due to their complex interactions and functional redundancy.
Human Activity and Its Effects on Ecosystem Resilience and Stability
- Negative Impacts:
- Deforestation, urbanization, and agricultural expansion reduce habitat complexity and species diversity, undermining ecosystem resilience and stability.
- Chemical pollutants, such as pesticides and heavy metals, can disrupt ecological processes and reduce biodiversity.
- Global warming and changing weather patterns alter habitat conditions, affecting species distribution and ecosystem functions.
- Positive Interventions:
- Protecting natural habitats and promoting biodiversity through conservation practices can enhance ecosystem resilience and stability.
- Ecological restoration aims to recover degraded ecosystems by reintroducing native species and restoring ecological functions.
- Implementing sustainable agricultural, forestry, and urban planning practices can mitigate the negative impacts of human activity on ecosystems.
image from femsre.oxfordjournals.org
HL Only
This unit is a minimum of 5-6 hours
2.5.9 The type of community that develops in a succession is influenced by climatic factors, the properties of the local bedrock and soil, geomorphology, together with fire and weather-related events that can occur. There can also be top-down influences from primary consumers or higher trophic levels.
- Outline the factors that influence community development
- Explain the role of geomorphology in determining the type of community that develops during succession.
- Explain how top-down influences from primary consumers or higher trophic levels can affect the final community structure in an ecosystem.
The type of community that develops during ecological succession is shaped by a variety of factors. These include climatic conditions, the properties of local bedrock and soil, geomorphology, and disturbance events such as fire and weather-related occurrences. Additionally, top-down influences from primary consumers or higher trophic levels can significantly impact the final community structure.
Factors Influencing Community Development
Top-Down Influences:
Factors Influencing Community Development
- Climatic Factors:
- The overall climate of an area, including its temperature and precipitation patterns, primarily determines the types of climax communities that can develop. For example, temperate forests, grasslands, and deserts all have distinct climatic conditions that support different types of climax communities.
- Properties of Local Bedrock and Soil:
- Soil composition, nutrient availability, and pH levels vary depending on the underlying bedrock and past biological activity. For instance, dense clay soils may become waterlogged, hindering plant growth, whereas sandy soils may drain too quickly, causing drought stress.
- The type of parent rock influences soil characteristics. Ultra-basic rocks, for instance, can create soils with high pH levels, affecting the types of plants that can thrive.
- Geomorphology:
- he shape and features of the landscape, such as slopes, valleys, and aspect (direction a slope faces), influence water drainage, soil formation, and sunlight exposure. Steep slopes may restrict soil development, slowing succession or preventing the establishment of a climax community.
- Areas with poor drainage can become waterlogged, creating anaerobic conditions unfavorable for many plants, thus influencing the types of species that establish.
- Fire and Weather-Related Events:
- Fire can act as a reset mechanism in ecosystems, burning existing vegetation and leading to secondary succession. Fire-adapted species may dominate initially, influencing the trajectory of succession.
- Severe weather events such as floods, droughts, or storms can disrupt ecosystems, causing regression to earlier successional stages and altering the pathway towards a climax community.
Top-Down Influences:
- Primary Consumers and Higher Trophic Levels:
- Herbivores: Grazing by herbivores like deer or elephants can shape plant community composition by preferentially consuming certain species, allowing others to dominate.
- Predators: Apex predators, such as wolves, can induce trophic cascades. For example, the removal of wolves from Yellowstone National Park led to an increase in elk populations, which overgrazed certain plant species, altering the plant community structure and impacting other species in the food web.
Case Studies:
Wolves in Yellowstone National Park:
- The removal and later reintroduction of wolves in Yellowstone caused significant changes in the ecosystem. Without wolves, elk populations increased, leading to overgrazing of young trees and shrubs. The reintroduction of wolves reduced elk numbers, allowing vegetation to recover, which in turn supported greater biodiversity.
- Elephants act as ecosystem engineers by knocking down trees and creating open spaces, which promotes grass growth and affects the types of species that can thrive in these areas. Their activity helps maintain a balance between wooded areas and grasslands, supporting diverse plant and animal communities.
2.5.10 Patterns of net productivity (NP) and gross productivity (GP) change over time in a community undergoing succession.
- Describe how GPP changes from early to late stages of succession.
- Explain why NPP is high in the early stages of succession but approaches zero in a climax community.
As ecological succession progresses, patterns of net productivity (NP) and gross productivity (GP) change significantly. In the early stages, GP is initially low due to unfavorable conditions and a low density of producers. However, as succession advances and the ecosystem matures, both GP and NP undergo notable transformations.
Primary Productivity: Review
Primary Productivity: Review
- Gross Primary Productivity (GPP):
- Definition: The total amount of energy or biomass per unit area per unit time that is fixed by the producer community through photosynthesis.
- Net Primary Productivity (NPP):
- Definition: The amount of energy or biomass that remains after subtracting the energy used for cellular respiration by producers from GPP.
- Formula: NPP = GPP - Respiration losses (R).
Changes Through Succession
Pioneer Community:
- Gross Productivity (GP): Low, due to the limited number of producers and harsh initial conditions.
- Net Productivity (NP): High, because respiration losses are minimal and the system is rapidly growing and accumulating biomass.
- Characteristics: Pioneer species such as lichens and mosses begin soil formation and establish the initial vegetative cover.
- Gross Productivity (GP): Increases as soil quality improves and more plant species establish, enhancing photosynthesis.
- Net Productivity (NP): Remains relatively high but starts to decrease as the community becomes more complex and respiration losses increase.
- Characteristics: Shrubs and small trees establish, leading to increased biodiversity and structural complexity.
- Gross Productivity (GP): High, due to the dense and diverse producer community capable of high photosynthetic activity.
- Net Productivity (NP): Approaches zero because the energy used for respiration by both producers and consumers balances out the high GP.
- Characteristics: A stable and mature ecosystem with a balanced energy budget, high biodiversity, and efficient nutrient cycling.
Summary
CHANGES THROUGH SUCCESSION
2.5.11 r- and K-strategist species have reproductive strategies that are better adapted to pioneer
and climax communities, respectively.
and climax communities, respectively.
- Compare and contrast r and K strategist species including their roles in succession.
- Demonstrate how reproductive strategies change between pioneer and climax communities.
- Distinguish the roles of r and k strategists in succession.
image from yesitsyomoma.wordpress.com
The terms r-selection and K-selection have also been used by ecologists to describe the growth and reproductive strategies of various organisms. Those organisms described as r-strategists typically live in unstable, unpredictable environments. Here the ability to reproduce rapidly (exponentially) is important. K-strategists, on the other hand occupy more stable environments. They are larger in size and have longer life expectancies. They are stronger or are better protected and generally are more energy efficient.
In general, communities in early succession will be dominated by fast-growing, well-dispersed species (opportunist, fugitive, or r-selected life-histories).
As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species. They tend to inhabit relatively stable biological communities, such as late-successional or climax forests
In general, communities in early succession will be dominated by fast-growing, well-dispersed species (opportunist, fugitive, or r-selected life-histories).
As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species. They tend to inhabit relatively stable biological communities, such as late-successional or climax forests
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K - Selected
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r - selected
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2.5.12 The concept of a climax community has been challenged, and there is uncertainty over what ecosystems would develop naturally were there no human influences.
- Describe what is meant by alternative stable states in the context of ecological succession.
- Summarize the main idea of the Vera wood-pasture hypothesis and its implications for understanding European landscapes after the last ice age.
- Discuss why there is uncertainty over what ecosystems would develop naturally without human influences.
The concept of a climax community—a stable endpoint in ecological succession—has long been a cornerstone of ecological theory. However, this idea has been challenged, and there is growing uncertainty about what ecosystems would naturally develop without human influences. The debate includes concepts like the Vera wood-pasture hypothesis and alternative stable states that result from random events.
Climax Community: Traditional View
Challenges to the Climax Community Concept
Climax Community: Traditional View
- Definition: A climax community is traditionally seen as the final, stable community in the process of ecological succession. It is characterized by a stable population of species that remain until disrupted by a disturbance.
- Stability: In this view, the climax community represents a state of equilibrium where ecological processes such as energy flow, nutrient cycling, and species interactions are balanced.
Challenges to the Climax Community Concept
- Alternative Stable States:
- There is no single climax community for any given ecosystem. Instead, multiple stable states are possible, depending on various factors such as climate, soil properties, and random events.
- Alternative stable states suggest that different communities can be equally stable under similar environmental conditions but may follow different successional paths due to historical contingencies and disturbances.
- Research and Evidence:
- Studies of lake core samples and peat bogs have provided insights into historical vegetation changes, suggesting that what we see as a climax community might be just one of several possible stable states. These studies highlight the influence of non-living (allogenic) factors that can alter the environment and lead to changes over time.
- Vera wood-pasture Hypothesis
- The Vera wood-pasture hypothesis, proposed by Frans Vera, challenges the idea that temperate Europe was covered by dense, untouched forests after the last ice age. Instead, Vera suggests that the landscape was a mosaic of open grasslands, scattered trees, and wooded pastures maintained by large herbivores such as aurochs and tarpans.
- Implications:
- This hypothesis emphasizes the role of large herbivores in shaping vegetation patterns and suggests that grazing animals can significantly influence and even prevent forest growth.
- Vera's work has influenced the rewilding movement, which aims to restore natural processes and wildlife populations in degraded ecosystems.
- Debate:
- While Vera's idea of a Europe dominated by savannas during the early to mid-Holocene has not gained widespread acceptance, it has sparked considerable debate and research. The hypothesis highlights the importance of considering the impact of grazing animals on woodland ecosystems.
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2.5.13 Human activity can divert and change the progression of succession leading to a plagioclimax.
- List the ways in which humans can disrupt the process of succession.
- Discuss the link between ecosystem stability, succession, diversity, and human activity.
- Explain how the diversion may end in a permanent or temporary alternative stable state.
- Discuss how human activity impacts ecosystem stability, succession and diversity
Human activity is one factor which can divert the progression of succession to an alternative stable state, by modifying the ecosystem, for agriculture, grazing pressure, or resource use such as deforestation. This diversion may be more or less permanent depending upon the resilience of the ecosystem.
Human activities often simplify ecosystems, rendering them unstable, for example, North American wheat farms versus tall grass prairie. An ecosystems capacity to survive change may depend on diversity, resilience and inertia
Human activities often simplify ecosystems, rendering them unstable, for example, North American wheat farms versus tall grass prairie. An ecosystems capacity to survive change may depend on diversity, resilience and inertia
Concept of Plagioclimax
Examples of Human Activities Leading to Plagioclimax
Implications of Plagioclimax Communities
- A plagioclimax community is a stage in succession that is maintained by regular human disturbance, preventing further natural succession and the establishment of a climax community.
- These communities are often less diverse than natural climax communities. They are maintained through practices such as mowing, grazing, burning, and deforestation.
Examples of Human Activities Leading to Plagioclimax
- Removal of Top Carnivores:
- Impact: The removal of top carnivores such as wolves or large cats can lead to an overpopulation of herbivores. Without predators to keep their numbers in check, these herbivores can overgraze vegetation, preventing the natural progression of plant succession.
- Example: In many parts of Europe and North America, the removal of wolves has led to overpopulation of deer, which heavily graze young trees and shrubs, preventing forest regeneration.
- Grazing by Domesticated Livestock:
- Impact: Continuous grazing by livestock such as cattle, sheep, and goats can halt the succession process by preventing the establishment of shrubs and trees.
- Example: In many agricultural areas, fields are maintained as grasslands due to constant grazing, preventing the natural succession to forested areas.
- Agriculture:
- Impact: Farming activities, including plowing, planting, and harvesting, continually disturb the soil and vegetation, maintaining early successional stages and preventing natural succession.
- Example: Cropland is regularly plowed and harvested, keeping it in a perpetual state of early succession.
- Urban Development:
- Impact: The construction of buildings, roads, and other infrastructure replaces natural habitats and prevents natural succession.
- Example: Urban areas are kept in a permanently altered state with little to no progression towards a climax community.
Implications of Plagioclimax Communities
- Biodiversity:
- Plagioclimax communities often have lower biodiversity compared to natural climax communities because the constant disturbance limits the variety of species that can establish and thrive.
- Ecosystem Services:
- These communities may provide different ecosystem services compared to natural climax communities. For instance, managed grasslands may support grazing livestock but lack the carbon sequestration capabilities of a mature forest.
- Conservation and Management:
- Understanding the role of human activities in creating plagioclimax communities is crucial for effective conservation and land management strategies. Efforts may focus on either maintaining these human-influenced ecosystems for their specific benefits or restoring natural successional processes to enhance biodiversity and ecosystem resilience.
You need to be able to discuss the factors which could lead to alternative stable states in an ecosystem, and discuss the link between ecosystem stability, succession, diversity, and human activity.
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.12601
Key Terms
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zonation
primary succession secondary succession seral community environmental gradient HL ONLY r-strategy k-strategy geomorphology allogenic factors plagioclimax community: |
latitude
altitude longitude disturbance |
stratified
fertile pioneer species limiting factor climax community |
gross productivity
net productivity stability species diversity |
trophic cascade
top-down Influence sere resilience |
Classroom Materials
| Subtopic 2.4 Zonation, Succession and Change in Ecosystems Workbook.docx |
| Subtopic 2.4 Zonation, Succession and Change in Ecosystems.pptx |
Succession and Zonation Cards activity
Savannah Succession activity
r and k Strategists review worksheet
Case Studies
- One case study of zonation
- One case study with named pioneer, intermediate and climax species for primary succession
- One case study with named pioneer, intermediate and climax species for secondary succession
- Named species for compare and contrast between r- and k-strategists
Mountain altitude zonation
Mt. Saint Helen
Abandon car lot
Amazon Rainforest
Useful Links
r and K Strategies Animation - McGraw Hill
Primary Succession animation - yTeach
Mt St. Helen's
Primary and Secondary Succession - GeoWords
An Example of Secondary Succession - Wiley
Succession: A Closer Look. - Nature
Example Secondary Succession - Offwell Woodland and Forest Trust
Succession Case Studies - Marietta College
Life After People - History
In The News
r and K Strategies Animation - McGraw Hill
Primary Succession animation - yTeach
Mt St. Helen's
Primary and Secondary Succession - GeoWords
An Example of Secondary Succession - Wiley
Succession: A Closer Look. - Nature
Example Secondary Succession - Offwell Woodland and Forest Trust
Succession Case Studies - Marietta College
Life After People - History
In The News
International-mindeness
- Zonation occurs on different scales that can be both local and global
Theory of knowledge:
- To what extent does our understanding of primary succession and the development of climax communities influence our approach to environmental conservation and restoration?
Video Clips
Paul Andersen explains the differences between an r and a K selected species. He starts with a brief description of population growth noting the importance of; r or growth rate, N or number of individuals in the population, and K the carrying capacity. He describes three different survivorship curves found in organisms. He lists the characteristics of r-selected species like bacteria and K-selected species like humans.
In the world of ecology, the only constant is change - but change can be good. Today Hank explains ecological succession and how ecological communities change over time to become beautiful, biodiverse mosaics.
Discover a process that truly demonstrates nature's grit: ecological succession!
Paul Andersen describes the process of ecological succession. During this process life reestablished itself after a disturbance. During primary success all of the material is removed including the soil. For example during a volcanic eruption all traces of life are removed. However during secondary success the soil remains intact. An example of secondary success is wildfires.
he ecosystem of Mount St. Helens continues to recover 30 years after the May 18, 1980 eruption
Succession, disturbances and the difference between man-made and natural disturbances and how land owners can use disturbance practices to mimic nature.
Fire ecologist and Ph.D candidate Emily Booth discusses the future of the Lost Pines of Bastrop State Park, as well as her role in cataloguing the forest's recovery
