IB Environmental systems and societies 3.1F Human Activities and Selective Forces Notes

Human Activities as Selective Forces

1. Human activities are now a major driver of selection pressures on other species.
2. These pressures can cause evolutionary change over very short time spans.

Climate Change as an Evolutionary Pressure

1. Burning fossil fuels alters temperature and rainfall, forcing species to adapt.
2. Some are evolving heat tolerance or shifting their breeding cycles.
3. Because the change is so rapid, many species cannot adapt in time, so extinction risk rises.

Hunting, Poaching, and Selection for Smaller Traits

1. Human hunting changes which traits are common in a population.
2. Overharvesting the largest individuals selects for smaller or tuskless forms.

Case study

• In Gorongosa, Mozambique, heavy ivory poaching during the civil war favoured elephants born without tusks.
• The share of tuskless females rose from about 2% to nearly 50%.

Habitat Modification and Fragmentation

1. Urbanisation, agriculture, and deforestation fragment habitats and isolate populations.
2. Fragmented populations face genetic drift, reduced gene flow, and new pressures, which can drive allopatric speciation.
3. Species in human-dominated areas often evolve traits such as:
   1. Tolerance to pollution.
   2. Adaptation to noise and artificial light.
   3. Altered feeding habits, such as scavenging human waste.

Introduction of Invasive Species

1. Humans move non-native species around the world.
2. Invasive species create new competition and predation, forcing native species to evolve.

Artificial Selection and Genetic Diversity

1. Artificial selection is the intentional breeding of organisms for desired traits.
2. Unlike natural selection, the selecting agent is human choice, not environmental pressure.

How Artificial Selection Works

1. Identify individuals with a desirable trait, such as high yield or disease resistance.
2. Breed them together to concentrate the trait.
3. Repeat over generations until the trait is stable.
4. Unwanted variants are excluded, which reduces genetic diversity.

Reduced Genetic Diversity as a Consequence

1. Artificial selection narrows the gene pool, because only a few individuals contribute genes.
2. A smaller gene pool means less capacity to adapt, lowering resilience to pests, disease, and climate change.
3. Genetic uniformity is efficient in the short term but a real ecological and economic risk.

Economic and Environmental Trade-offs

1. Economic value
   1. Raises production efficiency in crops and livestock and supports food security.
   2. But it pushes farming toward monoculture.
2. Environmental impact
   1. Reduces resilience to climate change, pests, and disease.
   2. Erodes the wild relatives that act as genetic reservoirs.