Human Populations (DP IB Environmental Systems & Societies (ESS))

Human Population Growth

Limiting factors on human population growth

• Human societies are increasingly able to overcome the limiting factors that once slowed down the growth of human populations

  • As well as allowing human population to dramatically increase in size in over the last few hundred years, this also has many negative consequences for the sustainability of ecosystems

• The main reasons humans have been able to eliminate these limiting factors include:

1. Elimination of natural predators:

   • Removal of natural predators like wolves or big cats has led to unchecked growth in certain human populations

   • This has also resulted in imbalances in ecosystems, such as overgrazing by deer populations due to the absence of wolves

     • For example, in Yellowstone National Park, reintroduction of wolves helped control the elk population, which in turn allowed vegetation to regenerate and stabilised the ecosystem

2. Technological advances:

   • Technological advancements in agriculture and medicine have reduced mortality rates and increased food production

   • This has led to exponential population growth as more people survive and reproduce

     • The Green Revolution in the mid-20th century, with the introduction of high-yield crop varieties and modern agricultural techniques, significantly increased food production globally

3. Degradation of the environment:

   • Our degradation of the environment has allowed humans to extract valuable resources like timber, minerals and fossil fuels

   • Clearing of forests for agriculture and urbanisation provides more living space and land for food production, increasing human population growth rates

     • Environmental degradation continues to facilitate the extraction of energy sources, such as fossil fuels, which are vital for sustaining growing populations

   • However, these activities also disrupt ecosystems, leading to habitat destruction, pollution and resource depletion

     • Negative impacts on biodiversity and ecosystem services compromise the sustainability of ecosystems and eventually their ability to support human populations

Assessing carrying capacity for human populations

• Scientists use various methods to estimate the carrying capacity of an environment for a given species

  • These methods include field observations, population surveys, mathematical modelling and data analysis

  • By studying population trends, resource availability and species interactions, researchers can make informed estimates of carrying capacity

• However, estimating carrying capacity becomes challenging when it comes to human populations due to several reasons:

The broad and changing ecological niche of humans

• Populations in ecosystems tend to reach equilibrium when the availability of resources matches the population's needs

• However, humans have a broad and dynamic ecological niche, constantly adapting through technological innovations and changes in consumption patterns

1. Mobility of resources:

   • Humans have the ability to move and exploit resources beyond their immediate habitat

   • This mobility complicates the assessment of carrying capacity, as humans can draw resources from distant locations

     • For example, global trade allows societies to access resources like food and materials from around the world, solving the problem of local resource limitations

2. Technological advancements:

   • Human societies have the ability to modify their environment and overcome traditional carrying capacity limitations through technology

     • For example, the development of agriculture and irrigation techniques has allowed humans to increase food production and support larger populations beyond what the natural environment could sustain

3. Cultural and social factors:

   • Human population dynamics are influenced by cultural norms, social behaviours and economic factors

     • For example, these can affect fertility rates and migration patterns, making it difficult to accurately predict or estimate carrying capacity for human populations

4. Changing lifestyles and consumption patterns:

   • Human populations are characterised by varying lifestyles and consumption rates, which can significantly impact resource demands and environmental impacts

     • For example, urbanised societies with high levels of consumption may strain the carrying capacity of their surrounding areas due to increased resource demands and waste generation

5. Adaptive capacity:

   • More so than any other species, humans have the ability to adapt and innovate in response to changing environmental conditions

   • This adaptability can affect carrying capacity by influencing resource use efficiency and the development of technological solutions

Disputed estimates of carrying capacity

• Urbanisation and industrialisation continually reshape human habitats, making it challenging to estimate carrying capacity

• Estimates are often disputed due to uncertainties in factors like technology, consumption patterns and environmental degradation