Biology | Sustainability and change

Welcome to Sustainability and Change!

Hi future biologist! This chapter, Sustainability and change, is one of the most relevant and important topics you will study in the IB Biology course. It bridges the foundational concepts (like evolution and ecology) with the pressing challenges facing the planet today.

You will learn how living systems respond to large-scale environmental changes, particularly those driven by human activity, and explore the biological principles required to manage ecosystems sustainably. Don't worry if some concepts seem broad at first; we will break down the essential biological mechanisms involved!

1. Understanding Change: The Context of Natural Selection

Before diving into modern climate change, it is vital to remember the core biological mechanism that dictates how species respond to environmental pressures: Natural Selection. Sustainability challenges create new selective pressures.

Quick Review: Natural Selection in a Changing World

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. For a population to survive a rapid environmental change (like sudden warming or acidification), it must:

• Have pre-existing variation within the gene pool.
• Experience a selective pressure strong enough to favor certain adaptations.
• Have enough time for favored traits to become prevalent.

Key Takeaway: If environmental change happens too quickly, species cannot adapt fast enough, leading to potential extinction or significant range shifts. This is the central biological risk posed by rapid climate change.

2. Sustainability: Managing Ecosystems for the Future

Sustainability in a biological context refers to the ability to maintain ecological processes and biodiversity over long periods, ensuring that resources can continue to support both current and future generations.

What is Sustainable Resource Use?

Sustainability requires balancing human needs with the capacity of nature to regenerate resources. We often refer to the capacity of nature as Natural Capital.

• Natural Capital: The world's natural assets, which include geological reserves, soil, air, water, and all living organisms.
• Sustainable Yield: Using a renewable resource (like timber or fish) at a rate that allows the population or resource base to recover fully.

Analogy: Sustainable yield is like managing money in a bank. You can spend the interest earned (the sustainable yield/rate of regeneration), but if you spend the principal (the natural capital), the resource base eventually collapses.

Conservation of Biodiversity and Sustainable Management

Effective management strategies rely heavily on understanding ecological niches, population dynamics, and energy flow.

Sustainable Practices in Biodiversity Management:

1. Habitat Preservation: Protecting large, connected areas (e.g., national parks, marine protected areas) to allow species to maintain viable population sizes and move in response to climate change.
2. Sustainable Agriculture and Forestry: Practices that minimize soil degradation, limit the use of harmful chemicals, and ensure tree harvesting does not exceed the regeneration rate.
3. Restoration Ecology: Actively repairing degraded or damaged ecosystems (e.g., replanting mangroves, restoring wetlands) to improve their capacity for ecosystem services (like filtering water or storing carbon).
4. Culling and Species Management: In cases where introduced or invasive species threaten local biodiversity, controlled management (culling) may be necessary to restore balance.

Did You Know? Wetlands (like marshes and swamps) are incredibly valuable to sustainability. They act as natural sponges, filtering pollutants, providing habitat, and crucially, acting as powerful carbon sinks, meaning they store CO₂ efficiently.

3. Climate Change: Causes and Biological Mechanisms

Climate Change refers to long-term shifts in temperatures and weather patterns, primarily driven by the increase in greenhouse gases resulting from human activities.

The Enhanced Greenhouse Effect

The core mechanism of global warming is the Greenhouse Effect. This is a natural process, but human activity has enhanced it.

1. Short-wavelength radiation (light) from the Sun passes through the atmosphere and heats the Earth's surface.
2. The Earth radiates this energy back out as longer-wavelength infrared radiation (heat).
3. Greenhouse Gases (GHGs)—including carbon dioxide (\(CO_2\)), methane (\(CH_4\)), and nitrous oxide (\(N_2O\))—absorb this infrared radiation.
4. The GHGs re-radiate the heat back towards the Earth, trapping it and warming the lower atmosphere.

The Biological Link: The major cause of increased \(CO_2\) is the combustion of fossil fuels (oil, coal, gas) and deforestation. When trees (natural carbon sinks) are cut down, the stored carbon is released back into the atmosphere.

4. Biological Consequences of Climate Change

A small shift in global temperature can have massive biological consequences, affecting organisms at the molecular, population, and ecosystem level.

A. Changes in Timing (Phenology)

Phenology is the study of the timing of biological events, such as flowering, migration, or breeding. Warming temperatures disrupt these timings.

• If plants flower earlier, but the insect pollinators they rely on hatch later, this creates a phenological mismatch.
• If migratory birds arrive at their summer feeding grounds before the local insect population has peaked, they may starve.

B. Changes in Geographical Distribution (Range Shifts)

As the climate warms, species are forced to move to stay within their optimal temperature zone.

• Moving Poleward: Species in the Northern Hemisphere are generally observed moving their ranges towards the North Pole.
• Moving Upward: Mountain-dwelling species are forced to move to higher altitudes. If they reach the mountain peak (the 'top of the hill'), they have nowhere else to go and face extinction.

Common Mistake Alert: Students often forget that habitat availability limits range shifts. A species cannot move poleward if its preferred soil type or food source doesn't exist in the new location.

C. Specific Impacts on Ecosystems (SL and HL Content Focus)

1. Marine Ecosystems: Ocean Acidification

When atmospheric \(CO_2\) dissolves in seawater, it forms carbonic acid (\(H_2CO_3\)), increasing the water's acidity (lowering the pH). This is known as Ocean Acidification.

• Impact on Calcifiers: The increased acidity reduces the availability of carbonate ions (\(CO_3^{2-}\)), which are essential for marine organisms (like corals, mollusks, and plankton) to build their shells and skeletons made of calcium carbonate (\(CaCO_3\)).
• Coral Bleaching: Elevated sea temperatures cause corals to expel the symbiotic algae (zooxanthellae) living in their tissues, leading to bleaching and death. Since coral reefs are incredibly biodiverse habitats, their loss severely impacts marine life.

2. Terrestrial Ecosystems: Biome Shifts

Changes in temperature and precipitation fundamentally alter biomes (major life zones defined by climate).

• Increased frequency of droughts and heatwaves can lead to massive forest fires, converting carbon sinks into carbon sources.
• The boundary between tundras and forests (the boreal zone) is shifting poleward, changing the habitats available for arctic wildlife.

5. Biological Solutions: Mitigation and Adaptation

Addressing climate change and promoting sustainability requires both mitigation (reducing the causes) and adaptation (adjusting to the inevitable effects).

Mitigation Strategies (Reducing GHGs)

Biologists play a crucial role in developing natural methods to remove carbon from the atmosphere (known as carbon sequestration).

• Afforestation/Reforestation: Planting new forests (afforestation) or replanting forests that have been cut down (reforestation). Trees use photosynthesis to pull massive amounts of \(CO_2\) out of the air and store it as biomass (carbon sink).
• Carbon Capture in Soils: Implementing sustainable farming practices (like no-till farming or cover crops) that increase the amount of organic carbon stored in the soil.
• Algae Biofuels: Developing fast-growing algae that can be used to capture CO₂ and produce fuel, thereby replacing fossil fuels.

Adaptation Strategies (Adjusting to Change)

These strategies focus on helping ecosystems and species cope with the changes already underway.

• Genetic Resilience: Using selective breeding or genetic engineering to create crop strains that are more tolerant of heat, drought, or increased salinity.
• Assisted Migration: Moving endangered species to new, cooler geographical areas where they are projected to thrive in future climate scenarios. (Note: This is often controversial due to the risk of introducing new invasive species.)
• Building Corridors: Establishing habitat corridors that connect fragmented ecosystems, allowing species to safely shift their geographical ranges poleward or upward.

Key Takeaway: Sustainability requires understanding the balance between natural capital and human usage. Climate change imposes severe selective pressures, leading to phenological mismatches and range shifts. Biological solutions focus heavily on using photosynthesis and ecosystem management for carbon mitigation.