What Happens When 2 Rabbits Take Over an Island?

Summary

The video presents a model of two European rabbits introduced to a small, predator-free Mediterranean island. It illustrates how rapid reproduction can drive a population boom, followed by a severe crash when seasonal food supplies cannot support the population.

• Seasonal food supply: The island has an eight-month green season, when grass grows, and a four-month dry season, when food becomes scarce. In a good year, the grass could theoretically feed about 6,000 rabbits. However, the video stresses that long-term limits depend on food availability during the lean season—not at its peak.
• Rabbit reproduction: Pregnancy lasts about a month, and a female can become pregnant again soon after giving birth. Lola has five babies, and some early-born females breed in their first spring. Mothers nurse briefly and infrequently, while young rabbits begin leaving the nest at around three weeks.
• Digestion: Rabbits re-ingest soft droppings, allowing them to extract nutrients that were not absorbed during the first passage of grass through the digestive system.
• Seasonal breeding and survival: Breeding largely pauses during the dry summer. Rabbits rely on moisture in green grass, so the loss of fresh vegetation contributes to hunger and thirst.
• Population growth and natural limits: The modeled population rises from 17 rabbits in the first summer to 60 in the second, 1,000 by the fourth, and roughly 11,000 by year seven. Competition for nesting sites and embryo reabsorption slow reproduction, but these controls take effect too late to prevent overuse of the island’s resources.
• Effects on the ecosystem: As grass becomes scarce, rabbits strip bark from shrubs and consume seedlings. The shrubs die and fail to regenerate, leaving the island permanently changed.
• Drought-driven crash and recovery: In year nine, rainfall is 30% below normal. With about 10,000 rabbits entering the dry season, grass and then other food sources run out. The population falls to about 500 by the first autumn rains—a loss of roughly 95%. Rain then restores the grass, enabling the population to grow again.
• Long-term outcome: Over 40 years, the island’s population repeatedly rises and falls. The video’s answer for the population ten years after introduction is about 1,500 rabbits; it says roughly 85,000 were born in that period. All descend from Lola and Max. The central ecological lesson is that an environment’s carrying capacity is shaped by its worst conditions, not its most productive season.

Researchers and Sources Listed

• Tablado & Revilla (2012), PLoS ONE — rabbit population dynamics model.
• Handbook of the Mammals of the World, Vol. 6 (2016) — European rabbit (Oryctolagus cuniculus).
• Gibb, White & Ward (1985), New Zealand Journal of Ecology — litter size through the season.
• Myers & Poole (1962), CSIRO Wildlife Research — rabbit breeding in enclosures.
• PestSmart — rabbit biology, ecology and distribution.
• Noy-Meir (1975), Journal of Ecology — stability of grazing systems.
• Caughley (1976) — interactive grazing systems; the supplied source description is truncated.