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U3: Topic 1, U3: Topic 2 - Coggle Diagram
U3: Topic 1
3.1.4 Population Ecology
Population Growth Models
Exponential Growth (J-curve):
- rapidly accelerating growth rate
- ideal and unlimited environment (e.g. newly colonized/newly booming area)
- initial growth starts slowly (due to low, dispersed numbers) but quickly accelerates
- IRL, a population experiencing a J-curve pattern will eventually crash once available resources are completely depleted
Logistic Growth (S-curve):
- occurs when resources are limited or finite
- growth slows down as the population reaches its maximum capacity, meaning resources like food, shelter, and space are used up
- typically observed in a stable population occupying a fixed geographic space
Limiting Factors
Density Dependent Factors: The impact of these factors increases as the population size increases
- Biotic Examples:
- Competition for resources (e.g., between species like the Red-Tailed Hawk and Barred Owl sharing habitat and resources),
- Predation (leading to cyclical population dynamics between predator and prey, with the predator population following the prey population with a small lag)
- Disease (spreads more easily in larger populations).
- Abiotic Examples:
- Space
- Availability of nutrients.
Density Independent Factors: These factors impact the population regardless of its size
- Abiotic Examples:
- pollution,
- natural disasters
- extreme climatic events (like drought or cyclones).
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Carrying Capacity
Definition: The carrying capacity (K) is the size of the population that can be supported indefinitely on the available resources and services of that ecosystem
- dynamic and can alter based on changes in biotic or abiotic factors
- lowered (reduced K) if resource destruction or degradation occurs during a population overshoot period
- when population is less (<) than K → birth rate exceeds death rate.
- when population is greater than (>) K → death rate exceeds birth rate.
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3.1.1 Biodiversity
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Species Definition
Biological Species Concept: A species = organisms that can interbreed and produce viable, fertile offspring
Example: horses + donkeys (infertile) --> not same species
Limitations: doesn't work for fossils, asexual organisms, extinct species, or separated populations
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U3: Topic 2
3.2.3 Community Ecology
Species Interactions
The Competitive Exclusion Principle:
states that two species cannot occupy the same ecological niche indefinitely.
- Over time, one species will inevitably outcompete the other, leading to one of two outcomes: local extinction of the weaker species, or adaptation by one species to a different niche, species competition is for the same resources
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Evolutionary Radiation
- When niches are suddenly made available (e.g., after a mass extinction event wipes out incumbent species), the resulting reduction in competition can trigger rapid evolutionary radiation
- Surviving species quickly occupy and adapt to these newly opened niches, leading to the rapid formation of many new species from one or a few ancestral species
Defining Niches
An ecological niche is the functional role an organism plays in an ecosystem. It is defined by several key aspects:
- Habitat = The physical location where the organism lives.
- Functional Role = The "job" the organism performs within the community (e.g., producer, consumer, decomposer).
- Resource Utilisation = The specific food, water, and other resources the organism uses to survive.
- Interactions with other species = How it interacts with other organisms, including predators, competitors, and mutualistic partners.
- Environmental Tolerances= The range of abiotic factors (like temperature, pH, and salinity) it can withstand.
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3.2.2 Cycles of matter
The Carbon Cycle
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Carbon is the fundamental building block of all organic molecules (Carbohydrates, Proteins, Lipids, and Nucleic Acids).
The Nitrogen Cycle
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- Nitrogen is critical as it is essential for the formation of amino acids (building blocks of proteins) and nucleic acids (DNA / RNA).
- Atmospheric nitrogen gas (N2) makes up 78% of the air but is unusable by plants due to its strong triple bond. Plants require fixed forms, primarily Nitrates (NO3-) or Ammonium (NH4+).
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