Carrying Capacity

Carrying capacity refers to the maximum number of individuals or population that a specific environment can support sustainably, based on available food, habitat, water and other life necessities in that environment.

For example, an island may have resources to sustainably support 500 deer based on the grassland habitat available as food supply.

Factors Affecting Carrying Capacity

Availability of Resources

Ecosystems with more abundant resources, especially essentials like food and water, can generally support larger populations. For example, a large, nutrient-rich lake can support more fish than a small stream. Resources can fluctuate with seasons, impacting carrying capacity.

Competition Between Species

When multiple species compete for the same finite resources, it lowers the carrying capacity for each one. For example, lions and hyenas may have higher populations if not competing for prey. Introducing an invasive species can reduce native species populations by increasing competition.

Environmental Conditions Changes in weather, climate, geology and other environmental factors can expand or lower an ecosystem’s carrying capacity. For example, a drought that reduces plant growth subsequently reduces herbivore numbers.

Examples of Carrying Capacity

Bengal Tigers and Sundarbans

As per various studies, Sundarbans has a carrying capacity of around 4.7 Bengal tigers per 100 square kilometres based on spotted deer density and biomass available. Considering the over 2,300 square kilometre tiger occupied area (as per 2018 data and taking into account the fact that of the 4,266 square kilometres in Indian Sundarbans, 55% is forest land), tiger density here will come to around 4.3. This is as per a report titled “Tigers, Co-predators & Prey in India, 2022” which found 103 tigers. The report indicated that Bengal Tiger population in Sundarbans may be reaching or exceeding the ecosystem’s maximum sustainable number or carrying capacity. The Sundarbans tiger population has grown steadily from 70 in 2010.

The concern is that further expansion could reduce prey species populations and degrade the forest habitat quality. This highlights the need to closely monitor Sundarbans tiger and prey populations in relation to the ecosystem’s limited carrying capacity to support them.

African Savanna Elephants

Data suggests the savanna habitat can maintain only about 0.5 elephants per square kilometer, totalling 354,000 for all African savannas. Populations are currently estimated at double that level and threatening the ecosystem. Migration corridors are being established to areas with lower elephant density to avoid habitat destruction.

Overshoot and Collapse of Easter Island, Chile

It’s believed Easter Island once had forests covering over 16 million trees that supported tens of thousands of islanders. But excessive logging reduced forests drastically, and ecosystems collapsed, leaving only 2-3k trees. Subsequent famine, war and diseases reduced the human population to just 2-3k as the island could no longer support more people.

Carrying Capacity and Population Dynamics

As a population nears its carrying capacity, its growth rate slows down and the population stabilizes around the carrying capacity. Growth rates can increase rapidly below carrying capacity when abundant resources are available. However, species may overshoot carrying capacity, resulting in die-offs and decreased populations due to lack of resources until equilibrium is reached again.