Ecosystem stability and change

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Ecosystem Balance

Ecosystem balance refers to the number of animals an area can support for long periods.
If the balance is upset, the whole system could fail.
All organisms rely on resources the area can supply; any area can only support a limited number of animals.
If all grass and trees die, herbivores like zebra and elephants would die, and then carnivores like cheetah and hyena would also die.
Population growth of species over time is a factor used to see if an ecosystem is balanced.

Limiting Factors

Limiting factors are resources that limit the growth of a population, such as food, water, space, light, nutrients, oxygen, disease, temperature, and predation.
Low food supply or lack of space are examples of limiting factors that can cause population decline.
When resources are limited, populations may decline due to less offspring, higher death rates, or emigration.
Human activities like pesticides, herbicides, and habitat destruction can also limit population growth.
Weather can be a limiting factor; for example, rainfall limits reproduction of the Agave Americana plant.

Limiting factors threatening the Riverine Rabbit population

Carrying Capacity

Carrying capacity is the population size that an ecosystem can support indefinitely.
When population is small, resources are plentiful, birth rates are high.
As population increases, resources decrease, leading to higher death rates and lower birth rates.
Population levels off at carrying capacity when birth and death rates become stable.

Population size levelling off at carrying capacity

Natural Factors Disrupting Ecosystems

Natural disasters like floods, hurricanes, and droughts can severely disrupt ecosystems.
Ecosystems may recover from sudden natural disasters, but long-term changes like climate change may cause irreversible damage.
The extinction of dinosaurs is theorized to be due to a sudden climate change caused by a meteor strike.
Droughts and famines can cause death of many organisms, especially species dependent on water for reproduction like amphibians.

The dry landscape in Ethiopia and people collecting water during a drought and famine

Human Factors Disrupting Ecosystems

Modern humans have a huge impact on nature through land clearing, pollution, waste, and litter.
Poaching and over-harvesting of animals cause lasting damage to ecosystems.
Over-hunting of small animals can force carnivores to prey on domestic animals, leading to further killing.
Poaching of species like abalone (perlemoen) and Mopani worms can lead to local extinction and disrupt food chains.
The Riverine Rabbit is critically endangered due to habitat destruction and human invasion.

Abalone (perlemoen) in its natural environment and served as a delicacy

Pollution

Pollution is a major human-caused disruption to ecosystems.
Types of pollution include water pollution, air pollution, and land pollution.
Pollution can harm organisms directly and degrade habitats.
Individuals can reduce pollution by changing habits and reducing waste.

Posters encouraging reduction of pollution

Case Study: Yellowstone Wolves

In the early 1900s, wolves were killed off in Yellowstone, leading to elk overpopulation and decline of aspen trees.
Reintroduction of wolves in 1995 allowed aspen to regrow, increasing biodiversity.
Wolves controlled elk populations, which allowed vegetation to recover, benefiting beavers and other species.
The return of wolves also affected coyote populations, increasing rabbits and mice, which supported hawks, foxes, and badgers.
This case shows how changes in one population can affect many others in the ecosystem.

Food Chains and Food Webs

A food chain shows the flow of energy from one organism to the next.
A food web is a network of interconnected food chains.
Most organisms eat multiple things, so food webs are more realistic.
All organisms depend on two global food webs: aquatic (based on phytoplankton) and land (based on plants).
Humans are top predators in both food webs.

A caterpillar feeding on a plant

Energy Flow

Energy flows through an ecosystem: from the sun, to producers, to consumers — unlike matter, it is not recycled.
Some energy is lost as heat at every step of a food chain, so fewer organisms can be supported at each higher level.
If a disruption removes producers or breaks a link in a food chain, the flow of energy to the rest of the ecosystem is disrupted too.

Sunlight over a grassy field, illustrating the sun as the primary energy source for ecosystems

Stability and Change

Stability of populations is affected by changes to living and nonliving components of an ecosystem.
Small changes can cause large effects elsewhere in the ecosystem.
Natural and human disruptions can cause imbalances, but ecosystems may find a new balance.
Every part of an ecosystem has a role; removing one part can have cascading effects.
Nature tries to adjust to disruptions, but sometimes new balances cannot be found.

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1.What is the main source of energy for most ecosystems?
Easy
- AThe sun
- BThe moon
- CWind
- DSoil nutrients
2.Which of the following is a natural factor that can disrupt a balanced ecosystem?
Easy
- AFlooding
- BDeforestation
- CPollution
- DPoaching
3.What is the term for the maximum population size that an ecosystem can support over a long period?
Easy
- ACarrying capacity
- BLimiting factor
- CPopulation growth
- DBiodiversity
4.Which of the following are limiting factors in an ecosystem? (Select all that apply)
Easy
- AFood
- BWater
- CPredation
- DCarrying capacity
- EBiodiversity
5.Match the term to its definition.
Easy
- Producer
- Consumer
- Decomposer
- Makes its own food
- Eats other organisms
- Breaks down dead organisms
6.Arrange the following events in the order they occurred in Yellowstone National Park after wolves were removed.
Easy
- Elk populations increased
- Aspen tree populations declined
- Wolves were killed
- Beavers left the park
7.What happened to the elk population when wolves were removed?
Medium
- AIt increased
- BIt decreased
- CIt stayed the same
- DIt became extinct
8.The reintroduction of wolves increased the biodiversity of Yellowstone National Park.
Medium
True or false?

Soal lainnya

9.Which of the following are natural factors that can disrupt a balanced ecosystem? (Select all that apply)
Medium
- AFloods
- BHurricanes
- CPoaching
- DClimate change
10.A sudden natural disaster, such as flooding, can disrupt an ecosystem.
Easy
True or false?
11.Arrange the following events in the order they occurred in Yellowstone National Park after wolves were reintroduced.
Medium
- Elk populations decreased
- Aspen trees began to regrow
- Beavers returned
- Biodiversity increased
12.In the Yellowstone example, which organism was the keystone species that affected the entire ecosystem?
Medium
- AElk
- BWolf
- CBeaver
- DAspen
13.Which of the following is an example of a human factor that can disrupt an ecosystem?
Medium
- AFlood
- BHurricane
- CPoaching
- DClimate change
14.Human activities such as habitat destruction can limit the growth of populations.
Easy
True or false?
15.Match each limiting factor to its correct example.
Medium
- Food
- Space
- Weather
- Amount of grass available
- Territory size for a predator
- Rainfall affecting plant reproduction
16.In the Arctic Ocean food web, if the arctic cod were removed, which of the following organisms would be most directly affected?
Medium
- ASeals that eat arctic cod
- BPhytoplankton that produce food
- CPolar bears that eat seals
- DKiller whales that eat seals
17.In a balanced savanna ecosystem, there are more zebra than cheetah. Which statement best explains this observation?
Medium
- ACheetahs are more efficient hunters than zebras are at grazing.
- BEnergy is lost at each trophic level, so fewer organisms can be supported at higher levels.
- CZebras reproduce faster than cheetahs, so they always have more offspring.
- DCheetahs are often killed by other predators, reducing their numbers.
18.Which of the following are examples of human activities that can limit the growth of populations? (Select all that apply)
Medium
- AUsing pesticides
- BHabitat destruction
- CNatural flooding
- DIntroduction of invasive species
- EClimate change
19.A farmer notices that after applying a pesticide to control insects, the population of birds in the area declines. Which statement best explains this observation?
Hard
- AThe pesticide directly kills the birds.
- BThe pesticide reduces the insects that birds feed on, leading to food shortage.
- CThe pesticide attracts more predators to the area.
- DThe pesticide causes the birds to migrate to other areas.
20.Which part of the graph represents the carrying capacity?
Medium
- AThe initial exponential growth phase
- BThe point where the population levels off
- CThe point where the population crashes
- DThe point where the population starts to decline
21.In a study of a grassland ecosystem, researchers removed all the rabbits from a fenced area and observed changes over two years. Which set of results would best support the idea that rabbits are a keystone species?
Hard
- APlant diversity increased, and the population of hawks decreased.
- BPlant diversity decreased, and the population of hawks increased.
- CPlant diversity stayed the same, and the population of hawks stayed the same.
- DPlant diversity increased, and the population of hawks increased.
22.In the Yellowstone example, after wolves were reintroduced, the elk population decreased. Which of the following is the most likely direct effect on aspen tree populations?
Hard
- AAspen tree populations increased because elk grazing decreased.
- BAspen tree populations decreased because wolves ate them.
- CAspen tree populations stayed the same because wolves do not affect plants.
- DAspen tree populations first increased then decreased due to disease.
23.A balanced ecosystem can support an unlimited number of animals.
Easy
True or false?
24.Natural disasters like floods or hurricanes can cause severe disruptions to ecosystems, but the ecosystems recover eventually.
Easy
True or false?
25.The Riverine Rabbit is classified as endangered because there are fewer than 200 individuals left in South Africa.
Easy
True or false?
26.In the Yellowstone example, the removal of wolves caused the elk population to increase and aspen trees to decline.
Easy
True or false?
27.In the Yellowstone example, after wolves were reintroduced, the elk population increased, leading to a decline in aspen trees.
Easy
True or false?
28.Complete the sentence with the correct term.
Easy
A species that is at risk of becoming extinct is called ____.
29.Approximately how many Riverine Rabbits are left in South Africa?
Easy
30.What is the term for the ability of an ecosystem to recover from a disturbance?
Medium
31.In a study, a population of rabbits in a meadow has a carrying capacity of 500 individuals. If the current population is 400 and the birth rate is 50 per year, while the death rate is 20 per year, what will be the population size after one year? (Assume no emigration or immigration.)
Medium
32.If the carrying capacity is 400 individuals and the population is currently at 350, what is the maximum number of additional individuals that can be supported?
Medium
33.Complete the sentence about the Riverine Rabbit.
Easy
The Riverine Rabbit is critically endangered because its habitat is restricted to small areas of the ____ and many of its home areas have been invaded by ____.
34.Complete the sentence about the effect of removing phytoplankton from a marine ecosystem.
Easy
If phytoplankton were removed from a marine ecosystem, the primary consumers would lose their main ____ source, which would likely cause their populations to ____.
35.In the Yellowstone example, wolves were reintroduced in 1995. How many wolves were initially reintroduced?
Medium
36.What is the term for a species that has such a large effect on its ecosystem that its removal causes significant changes?
Medium
37.Complete the sentence about the effect of removing wolves from Yellowstone.
Medium
When wolves were removed from Yellowstone, the deer population ____, which led to over-eating of vegetation, increased ____, and caused many species like beavers to leave.
38.Explain why there are more zebra than cheetah in a balanced savanna ecosystem.
Medium
39.Explain how the reintroduction of wolves in Yellowstone affected the ecosystem's stability.
Hard
40.Explain what carrying capacity means and why limiting factors are important when working out an ecosystem's carrying capacity.
Hard
41.Lake Erie has experienced algal blooms during warm weather: cyanobacteria (blue-green algae) grow into thick mats that cover the surface of the lake, as shown below. Which statement best explains how this could affect populations of organisms living in the lake?
Medium
- AUnderwater plants and algae would get less sunlight, so they would produce less food through photosynthesis.
- BMussels would be unaffected because they feed only on zooplankton, never on algae.
- CToxins from the bloom would cause fish that eat other fish to increase in number.
- DBottom-feeding fish would move up near the surface to feed on the algae.
42.Human activity has been reducing giraffe habitat in Africa for decades, and giraffe numbers have been falling as a result. Which graph best shows the general relationship between the number of giraffes living in Africa and time?
Medium
- AGraph A: a curve that starts high and steadily decreases
- BGraph B: a curve that starts low and steadily increases
- CGraph C: a flat, unchanging line
- DGraph D: a curve that rises and falls repeatedly
43.Polar bears rely on a large amount of Arctic sea ice to hunt seals. What is most likely to happen to a polar bear population if the amount of Arctic ice decreases significantly over a short period of time?
Easy
- APolar bears will migrate south to reduce the effects of habitat loss.
- BMany polar bears will be unable to find enough food and the population will decline sharply.
- CPolar bears will quickly evolve larger bodies to store more fat.
- DPolar bears will quickly adapt to hunting fully in open water.

Catatan ulasan

## Ecosystem Stability and Change ### Key Concepts - **Ecological stability (equilibrium)**: An ecosystem's ability to return to its original state after a disturbance (resilience) or to avoid unexpected large changes over time. - **Resilience**: Capacity to recover after a perturbation. - **Persistence**: Ability to remain over time despite disturbances. - **Constancy**: Lack of change in a property (e.g., biomass, biodiversity). ### Stability vs. Instability - Not all ecosystems are stable. Example: wolves and moose on Isle Royale show fluctuating populations. - An ecosystem can be stable in some properties but unstable in others. Example: a vegetation community may conserve biomass but lose biodiversity during drought. ### Types of Stability (Grimm & Wissel, 1997) - Over 70 definitions exist. To avoid confusion, use specific terms like **constancy**, **resilience**, and **persistence**. - Example: A predator-prey cycle is persistent and resilient, but not constant. ### Stability Analysis (Robert May, 1970s) - Uses a **Jacobian matrix** (community matrix) to test stability near an equilibrium point. - Linearizes the system of differential equations: \[ \frac{dN_i}{dt} = g_i(N_1, \ldots, N_S), \quad i=1,\ldots,S \] At a fixed point \(N_1^\star, \ldots, N_S^\star\): \[ \frac{dN_i}{dt} = \sum_{j=1}^S J_{ij}(N_j - N_j^\star) \] The fixed point is **linearly stable** if all eigenvalues of the Jacobian have negative real parts. ### May's Random Matrix Theory - May applied random matrix ideas to large ecosystems with \(S\) species. - Stability depends on the strength and pattern of interactions. - **Key insight**: Highly diverse or strongly interacting systems may be less stable. ### Takeaway for Exam - Understand the difference between resilience, persistence, and constancy. - Know that stability is not a single property; an ecosystem can be stable in one aspect and unstable in another. - Remember that stability analysis uses eigenvalues of the Jacobian matrix. - Be able to give examples: stable grasslands vs. unstable predator-prey dynamics.

Ecological stability: The ability of an ecosystem to return to its equilibrium state after a perturbation (resilience) or to avoid unexpected large changes over time.
Resilience: The capacity of an ecosystem to recover after a disturbance.
Persistence: The ability of an ecosystem or community to continue existing over time despite disturbances.
Constancy: Lack of change in a particular property of an ecosystem (e.g., biomass, species richness) over time.
Jacobian matrix: A matrix of partial derivatives used in stability analysis to determine if an equilibrium point is stable by checking eigenvalues.
Linear stability: A fixed point is linearly stable if all eigenvalues of the Jacobian matrix have negative real parts, meaning small perturbations decay over time.

Kartu flash

What is ecological stability?

Ecological stability is the ability of an ecosystem to return to its equilibrium state after a disturbance (resilience) or to avoid unexpected large changes over time.

What is resilience in an ecosystem?

Resilience is the capacity of an ecosystem to return to its equilibrium state after a perturbation or disturbance.

Can an ecosystem be stable in some properties but unstable in others?

Yes, for example, a vegetation community during a drought might conserve biomass (stable) but lose biodiversity (unstable).

Give an example of a naturally unstable ecosystem.

The wolf and moose populations on Isle Royale are an example of an unstable ecosystem, as they do not remain constant over time.

What role does noise play in biological systems?

Noise (random fluctuations) can significantly influence biological systems and, in some cases, fully determine their temporal dynamics.

What are three specific terms that can replace 'ecological stability' for clarity?

Constancy, resilience, and persistence are more specific terms that can describe different aspects of stability.

Define constancy in ecology.

Constancy refers to an ecosystem's ability to remain unchanged or vary within narrow limits over time.

Define persistence in ecology.

Persistence is the ability of an ecosystem to continue existing over time, even if it undergoes fluctuations.

How would you describe an ecosystem that oscillates cyclically around a fixed point (e.g., predator-prey cycles)?

Such an ecosystem would be described as persistent and resilient, but not constant.

What is the Jacobian matrix used for in ecology?

The Jacobian matrix (or community matrix) is used in stability analysis to test whether an ecosystem's equilibrium point is stable by examining its eigenvalues.

What did Robert May investigate using stability analysis in the 1970s?

Robert May used stability analysis to investigate the relationship between the diversity and stability of an ecosystem.

How did May analyze large ecosystems?

May used random matrix theory, assuming the ecosystem's interactions could be approximated by a random matrix, to study stability properties.

What is a fixed point in an ecosystem model?

A fixed point is an equilibrium state where species abundances remain constant over time, such that dN_i/dt = 0 for all species.

What condition must be met for a fixed point to be linearly stable?

All eigenvalues of the Jacobian matrix must have negative real parts for the fixed point to be linearly stable.

What does it mean if an ecosystem is 'linearly stable'?

Linear stability means that after a small perturbation, the system will return to its equilibrium state.

What is a perturbation in ecology?

A perturbation is a disturbance or change that affects an ecosystem, such as a drought, fire, or introduction of a new species.

How can changes to physical components of an ecosystem affect populations?

Changes like temperature shifts or water availability can alter habitats, food sources, and survival rates, leading to population changes.

How can changes to biological components of an ecosystem affect populations?

Changes like introduction of a predator or disease can reduce prey populations, while removal of a species can cause cascading effects.

What is dynamic equilibrium in an ecosystem?

Dynamic equilibrium is a state where ecosystem properties fluctuate around a stable average, maintaining overall balance despite changes.

What is ecosystem resilience?

Ecosystem resilience is the speed and ability of an ecosystem to recover from a disturbance and return to its original state.

What is the difference between resilience and constancy?

Resilience is the ability to recover after disturbance, while constancy is the ability to remain unchanged.

Why is biodiversity important for ecosystem stability?

Higher biodiversity can provide functional redundancy, making ecosystems more resilient to disturbances.

What happens when an ecosystem loses its resilience?

It may shift to a different state (e.g., grassland to desert) and not return to the original equilibrium.

Give an example of a human activity that can disrupt ecosystem stability.

Deforestation can remove habitat, alter water cycles, and reduce biodiversity, destabilizing the ecosystem.

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