D4.2  Stability and Change

Theme:  Continuity and Change

Established ecosystems tend to demonstrate stability.

• Stability is often dependent on a single species. Keystone species maintain the structure of the the food web.
• Stability is a product of negative feedback loops. For example, the interaction between predators and prey prevents any one population from exploding and destroying the resource base.
• In the absence of major disturbances, ecosystems tend toward a "climax" state. This represents a long-term continuity where the species composition remains relatively unchanged over vast periods of time.

Ecosystems can change, either through slow, predictable stages or sudden, irreversible shifts.

• Succession is a structured process of predictable change in species diversity and biomass over time. During primary succession, pioneer species change the environment by forming soil to allow for later species to establish. Secondary succession occurs after a disturbance like a forest fire.
• Some ecosystems depend on regular change to maintain their continuity. For example, some pine forests require periodic fires to release seeds.
  
• If a disturbance is too great, an ecosystem can reach a "tipping point" and rapidly shift into a completely different state. For example, a clear-water lake can change into a turbid, algal-dominated pond.
  
• Anthropogenic factors, such as climate change or the introduction of invasive species, represent unnatural changes that can permanently disrupt the stability of an ecosystem, leading to a loss of biodiversity.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What features of ecosystems allow stability over unlimited time periods?
• What changes caused by humans threaten the stability of ecosystems?​

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What is the distinction between artificial and natural processes? 
• Over what timescales do things change in different biological systems? 

Key Terms to Know: * higher level only

Abiotic*
Agriculture
Agrochemical
Amazon Rainforest
Apex Predator
Arrested Succession*
Atmospheric Water Vapor
Biochemical Oxygen Demand
Biomagnification
Biotic*
Carbon Footprint
Climax Community*
Connectivity of Habitats
Consumer (Food Chain)
Cyclical Succession*

DDT (as Pollutant)
Deforestation
Ecological Succession*
Ecosystem Stability
Eutrophication
Fertilizer
Hinewai Reserve
Human Impact
Keystone Species
Leaching (of Nutrients)
Microplastic
Mercury (as Pollutant)
Mesocosm
Microplastic
Nutrient Cycling*

Percent Change
Pollutant
Primary Production*
Primary Succession*
Resource Harvesting
Restoration
Rewilding
Soil Erosion
Species Diversity*
Sustainability
Tipping Point
Tolerance Level
Transpiration
Trophic Level

D4.2.1—  Stability as a property of natural ecosystems.

• Define stability as a property of an ecosystem.
• Describe an example of a stable ecosystem.​

D4.2.2— Requirements for stability in ecosystems.

• Outline requirements for stability in an ecosystem. 
• Outline types of environmental change that can interfere with ecosystem stability.

D4.2.3-- Deforestation of Amazon rainforest as an example of a possible tipping point in ecosystem stability.

• Define “tipping point” in relation to ecosystem stability. 
• Discuss the impact of Amazon deforestation as an example of an ecosystem at a tipping point.

D4.2.4-- Use of a model to investigate the effect of variables on ecosystem stability.

• Define mesocosm.
• Outline requirements of setting up a sustainable  mesocosm.
• Discuss the benefits and limitations of using mesocosms as models of ecosystems.​

D4.2.5— Role of keystone species in the stability of ecosystems.

• State the role of a keystone species in an ecosystem. 
• Outline an example of a keystone species in an ecosystem. ​

D4.2.6-  Assessing sustainability of resource harvesting from natural ecosystems.

• Describe requirements for sustainability in ecosystems. 
• Define resource harvesting. 
• Define sustainable in relation to resource harvesting. 
• Discuss the sustainable resource harvesting of a marine fish.  
• Assess the sustainability of resource harvesting by identifying the maximum sustainable yield of a resource on a population growth curve. 
• Discuss the sustainable resource harvesting of a terrestrial plant.  

 ​​​D4.2.7- Factors affecting the sustainability of agriculture.

• Discuss factors that negatively impact the sustainability of agriculture.

D4.2.8- Eutrophication of aquatic and marine ecosystems due to leaching.

• Discuss causes and effects of ecosystem eutrophication.

D4.2.9- Biomagnification of pollutants in natural ecosystems.

• Outline the process of biomagnification. 
• Discuss the cause and effect of mercury biomagnification in an ecosystem.  
• Discuss the cause and effect of DDT biomagnification in an ecosystem. 

D4.2.10- Effects of microplastic and microplastic pollution of the oceans.

• Define biodegradable. 
• State that plastics are not biodegradable. 
• Define microplastic and macroplastic. 
• Discuss the cause and effect of microplastic pollution on an ocean  ecosystem.  
• Discuss the cause and effect of microplastic pollution on an ocean ecosystem.  ​

D4.2.11- Restoration of natural processes in ecosystems by rewilding.

• Define rewilding.
• Discuss the methods of restoration of an ecosystem by rewilding.
• Outline the rewilding of the Hinewai Reserve in New Zealand.​

AHL ​​​​​​​D4.2.12- Ecological succession and its causes.

• Outline the cause and effect of ecological succession.
• Outline an example of reciprocal interactions between living organisms and the abiotic environments that cause ecological succession. 
• State an example of ecological succession triggered by an abiotic factor.
• State an example of ecological succession triggered by a biotic factor. ​

AHL ​​​​​​D4.2.13- Changes occurring during primary succession.

• Describe changes occurring during primary succession in a community, including increases in size of plants, amount of primary production, species diversity, complexity of food webs and amount of nutrient cycling.​

AHL ​​​​​​D4.2.14- Cyclical succession in ecosystems.

• Explain an example of cyclical succession in an ecosystem.​

AHL ​​​​​​D4.2.15- Climax communities and arrested succession.

• Define climax community and plagioclimax.
• Discuss the impact of grazing my farm livestock on arresting succession in a community.  
• Discuss the impact of drainage of wetlands on arresting succession in a community. ​