🌱 B19: Human Influences on Ecosystems – Study Notes
Hello future scientists! This chapter brings together everything we’ve learned about organisms and their environments (B18) and focuses on the biggest force for change: us! Understanding how human activities impact ecosystems is vital not just for the exam, but for understanding the world around you. Don't worry, we'll break down the big issues like habitat loss and climate change into clear, manageable steps.
1. Understanding Ecosystems and Biodiversity (The Basics)
Before looking at human influence, we need to quickly define the key units of nature.
Key Definitions
1. Ecosystem (Core 1)
An ecosystem is like "Nature's Neighborhood."
It is a unit containing the community of organisms and their environment, interacting together.
Example: A tropical rainforest (the community of plants and animals) interacting with the soil, climate, and rainfall (the environment).
2. Biodiversity (Core 2)
Biodiversity simply means the number of different species that live in an area.
The greater the number of different species, the higher the biodiversity. High biodiversity is usually a sign of a healthy, stable ecosystem.
Key Takeaway: We are looking at how our actions disrupt the stability (ecosystems) and variety (biodiversity) of life on Earth.
2. Habitat Destruction: The Main Threat (B19.1)
Habitat destruction is the process where a natural habitat is rendered unable to support the species present, often resulting in the displacement or extinction of that species.
Reasons for Habitat Destruction (Core 3)
Human populations are constantly growing, which requires more space and resources. This growth is the root cause of most habitat loss:
• Increased Area for Production: Land is cleared for housing, large-scale crop plant production (farming), and livestock production (cattle, sheep, etc.).
• Extraction of Natural Resources: This includes mining for minerals, quarrying for building materials, and drilling for oil and gas. These activities physically remove or contaminate the natural habitat.
• Freshwater and Marine Pollution: Pollutants entering water bodies destroy aquatic habitats. (Note: You need to know that pollution is a reason, but detailed descriptions of eutrophication are not required for the exam.)
Case Study: Undesirable Effects of Deforestation (Core 4 & Supplement 5)
Deforestation is the large-scale removal of trees and is a prime example of habitat destruction. The consequences are wide-reaching:
1. Reducing Biodiversity & Extinction:
When forests are cut down, habitats vanish. The organisms living there suddenly have nowhere to go, drastically reducing the number of species (biodiversity). This often leads directly to the extinction of species unique to that area.
2. Loss of Soil (Erosion):
Tree roots stabilize the soil. Without trees, heavy rain washes away the valuable topsoil (soil erosion). This makes the land infertile for future regrowth and damages nearby waterways.
3. Flooding:
Forests act like giant sponges, absorbing massive amounts of rainfall. When they are removed, water runs quickly over the surface, increasing the risk and severity of flooding downstream.
4. Increase of Carbon Dioxide in the Atmosphere:
Trees are carbon sinks—they absorb carbon dioxide (CO₂) during photosynthesis. When forests are cut down, less CO₂ is removed from the atmosphere. Furthermore, when the wood is burned or left to decompose, stored carbon is released back as CO₂, contributing to global warming.
Quick Review: The 5 Ds of Deforestation Effects
Decreased Diversity, Destruction (extinction), Dirt (soil loss), Deluge (flooding), Dioxide (increased CO₂).
3. Causes of Endangerment and Extinction (B19.2)
An organism is endangered if it is at high risk of extinction in the near future. An organism is extinct when there are no living individuals left anywhere in the world.
The transition from endangered to extinct is driven by several key human influences (Core 1):
1. Climate Change:
Changing global temperatures and weather patterns (due to greenhouse gases like CO₂ and methane) make environments unsuitable for certain species. Example: Polar bears struggle as sea ice melts.
2. Habitat Destruction:
(As discussed above) The simple destruction of the place a species lives (e.g., rainforest clearance, draining wetlands).
3. Hunting:
Illegal or excessive hunting (poaching) can rapidly deplete populations, especially large, slow-reproducing animals like rhinos or tigers.
4. Overharvesting:
This is the sustainable removal of resources faster than they can regenerate. Example: Overfishing, where fish stocks are caught quicker than they can reproduce, leading to population collapse.
5. Pollution:
The release of toxic materials, non-biodegradable plastics, or chemicals into the environment harms or kills organisms. Example: Oil spills, or pesticides accumulating up the food chain.
6. Introduced Species:
Humans sometimes intentionally or accidentally introduce foreign (non-native) species into new habitats. These non-native species often have no natural predators in the new ecosystem and can out-compete or prey upon the native species, leading to their decline.
Did you know? The brown tree snake introduced accidentally to Guam wiped out most of the native bird populations because the birds had no defenses against it.
Key Takeaway: All these factors reduce the population size, making species vulnerable to random events or disease, increasing their risk of extinction.
4. Conservation Methods (B19.2)
Conservation refers to the protection and management of natural resources, including wildlife and habitats.
To prevent further loss of biodiversity, conservation efforts focus on four main areas (Core 2):
1. Monitoring and Protecting Species and Habitats:
• Monitoring: Regularly counting species populations and assessing habitat health to identify problems early.
• Protection: Establishing national parks or marine reserves where damaging activities (like hunting or deforestation) are strictly banned or controlled.
2. Education:
Informing people (locals, governments, consumers) about the importance of biodiversity and the negative impacts of destructive practices. Education helps to change attitudes and behaviour, leading to sustainable practices.
3. Captive Breeding Programmes:
This involves breeding endangered animals in controlled environments (like zoos or special facilities) to increase their numbers safely. The ultimate goal is often to reintroduce these healthy populations back into the wild once their original habitat is protected.
Analogy: Captive breeding is like having an insurance policy for a species; if the wild population crashes, we have a backup ready.
4. Seed Banks:
These facilities store seeds from a huge variety of plants, especially those that are rare or endangered. They are essential reserves of genetic material that can be used for research, breeding, or reintroducing plant species if they become extinct in the wild.
Quick Review: Human Influences on Ecosystems
Destruction is Bad: Deforestation causes loss of soil, flooding, CO₂ increase, and extinction.
Causes of Loss: Habitat loss, climate change, hunting/overharvesting, pollution, and introduced species.
Conservation is Key: Monitoring, education, captive breeding, and seed banks.