Study Notes: B16 Human Influences on Ecosystems (Combined Science 0653)
Hello future scientists! This chapter is incredibly important because it connects everything we learn in Biology to the real world. We are going to explore how humans are impacting the environment and what we can do to help save our planet's wonderful diversity. Don't worry if some terms sound unfamiliar—we’ll break them down step-by-step!
B16.1 Habitat Destruction
What are Ecosystems and Biodiversity?
Before we discuss destruction, we need to know what we are destroying!
1. The Ecosystem
An ecosystem is like a complete package deal in nature. It is defined as a unit containing the community of organisms (all the living things, like plants, animals, and microbes) and their environment (the non-living parts, like air, water, and soil), all interacting together.
Example: A forest ecosystem includes all the trees, birds, insects, soil bacteria, water runoff, and air temperature, all influencing each other.
2. Biodiversity
Biodiversity is simply the number of different species that live in an area.
Think of it like a library: a library with 100 different types of books (fiction, science, history, poetry) has high biodiversity. A library with 100 copies of the exact same book has very low biodiversity, even though the number of individuals (books) is the same. The more different species an area has, the healthier and more stable the ecosystem usually is.
Quick Review:
* Ecosystem = Living Community + Non-living Environment (interacting).
* Biodiversity = Number of different species in that area.
Reasons for Habitat Destruction
Humans destroy habitats (the place where an organism lives) primarily because we need resources and space. The syllabus lists several key reasons:
1. Increased Area for Living and Farming:
(a) Expansion for housing (cities and towns grow).
(b) Expansion for crop plant production (growing food like wheat and rice).
(c) Expansion for livestock production (raising animals like cows and chickens).
2. Extraction of Natural Resources:
(a) Logging (cutting down forests for timber or paper).
(b) Mining (digging up minerals and metals).
3. Pollution:
(a) Pollution of freshwater and marine environments (waste, chemicals, oil spills).
(b) Note: You only need to know that freshwater and marine pollution cause habitat destruction; a detailed description of eutrophication is not required for this syllabus section.
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The Undesirable Effects of Deforestation (Supplement Explanation)
Deforestation (the large-scale cutting down of trees) is a prime example of habitat destruction. The effects are extremely damaging. You need to understand and be able to explain these four effects:
1. Reducing Biodiversity and Causing Extinction
Trees provide food and shelter for thousands of species. When a forest is cleared, many organisms lose their home immediately. This dramatically reduces biodiversity. If a species lives nowhere else, it faces extinction (it dies out completely).
2. Loss of Soil (Soil Erosion)
Tree roots act like glue, holding the soil together. When trees are removed, the soil is unprotected. Heavy rain and wind can easily wash or blow the fertile topsoil away. This is called soil erosion.
3. Flooding
Trees are vital for managing the water cycle. They absorb huge amounts of rainwater. Without trees, when it rains heavily, the water runs straight over the exposed land into rivers, increasing the risk of severe flooding downstream.
4. Increase of Carbon Dioxide in the Atmosphere
Trees absorb carbon dioxide ($\text{CO}_2$) during photosynthesis. Deforestation increases $\text{CO}_2$ in two ways:
a) Fewer trees: Less photosynthesis happens, so less $\text{CO}_2$ is removed from the atmosphere.
b) Burning/Decomposition: When the chopped trees are burned or left to decompose, the carbon stored within their wood is released back into the atmosphere as $\text{CO}_2$.
Higher $\text{CO}_2$ contributes to global warming and climate change.
Key Takeaway for Deforestation: Deforestation is bad because it leads to species loss, soil erosion, flooding, and an increase in atmospheric $\text{CO}_2$.
B16.2 Conservation
Conservation refers to the protection and management of natural resources, including ecosystems and species.
Why Organisms Become Endangered or Extinct
Species decline when their environment changes too quickly or when they are exploited faster than they can reproduce. Key reasons include:
1. Climate Change: Changing weather patterns (like increased heat or extreme rainfall) disrupt the environment and food sources that species rely on.
2. Habitat Destruction: The loss of their home (as discussed above, e.g., deforestation, drainage of wetlands).
3. Hunting: Killing animals, often illegally, for food, trophies, or traditional medicine (e.g., rhinos hunted for horns).
4. Overharvesting: Taking too many organisms from the wild (e.g., fishing large quantities of a specific fish species until their population cannot recover).
5. Pollution: Introducing harmful substances into the ecosystem (e.g., plastic waste or chemical pesticides).
6. Introduced Species: Bringing non-native (foreign) species into a habitat where they compete with or prey on native species, often without natural predators to control their numbers.
Did you know? The brown tree snake was accidentally introduced to Guam during WWII and almost wiped out the native bird populations because the birds had no natural defence against snakes.
Methods of Conservation (Supplement)
Protecting species requires specific actions. Here are four key ways endangered species are conserved:
1. Monitoring and Protecting Species and Habitats
This involves actively watching animal populations (monitoring) to track their health and numbers. It also means setting up and policing protected areas (like national parks or marine reserves) to prevent illegal activity like poaching or logging (protecting habitats).
How it works: Rangers patrol reserves to deter poachers, and scientists track individual animals using tags to ensure their safety.
2. Education
Conservation efforts rely heavily on public support. Education involves raising awareness about the importance of biodiversity and the threats facing species. This can change public behaviour (e.g., reducing plastic use, buying sustainable products) and increase support for conservation funding.
How it works: School programs, museum exhibits, and media campaigns teach people about endangered species.
3. Captive Breeding Programmes
These programmes involve breeding endangered animals in controlled human environments, like zoos or research facilities, until their numbers are high enough to potentially reintroduce them safely back into the wild.
Analogy: Think of it as a biological "nursery" where species that are too vulnerable in the wild can multiply safely.
4. Seed Banks
A seed bank is essentially a giant vault where seeds from thousands of different plant species are collected, stored, and frozen under controlled conditions. They serve as a backup to protect plant biodiversity against extinction, disease, or disaster.
How it works: If a wild crop is destroyed by disease, scientists can retrieve the stored seeds and regrow the plants.
Key Takeaway for Conservation: We combat extinction using protection (monitoring/reserves), awareness (education), breeding (captive programmes), and storage (seed banks).
Quick Study Review
Ecosystem: Living community + non-living environment.
Biodiversity: Number of different species.
4 Causes of Destruction:
1. Housing/Farming (Crops/Livestock)
2. Resource Extraction (Logging/Mining)
3. Pollution (Freshwater/Marine)
4 Effects of Deforestation (Dangers):
1. Reduced Biodiversity/Extinction
2. Loss of Soil (Erosion)
3. Flooding
4. Increased Carbon Dioxide
4 Methods of Conservation (Solutions):
1. Monitoring & Protecting (Patrols, Reserves)
2. Education (Raising awareness)
3. Captive Breeding (Zoos/Nurseries)
4. Seed Banks (Frozen storage)