# PTE RL #17: Invasive Species and Ecosystem...

Re-tell Lecture #17 - Level 3 - Feeds Speaking + Listening

> You will hear a lecture. When it ends, you have 10 seconds to prepare, then 40 seconds to retell the lecture in your own words.

## Explanation

The lecture explains that ecosystems rely on co-evolution, where species adapt to each other and their environment to reach a stable state. This balance is maintained by limiting factors like climate, food, and predators. The introduction of non-native species can disrupt this balance, often leading to negative impacts on the existing ecosystem.

## Hints

- Focus on the main concept of how species interact to maintain a stable environment.
- Note the role of limiting factors and the impact of introducing non-native species.

## Transcript

Most of the world's ecosystems are the result of millennia of co-evolution by organisms, adapting to their environment and each other until a stable balance is reached. Healthy ecosystems maintain this balance via limiting factors, environmental conditions that restrict the size or range of a species. These include things like natural geography and climate, food availability, and the presence or absence of predators. For example, plant growth depends on levels of sunlight and soil nutrients. The amount of edible plants affects the population of herbivores, which in turn impacts the carnivores that feed on them, and a healthy predator population keeps the herbivores from becoming too numerous and devouring all the plants. But even minor changes in one factor can upset this balance, and the sudden introduction of non-native organisms can be a pretty major change. A species that has evolved in a separate habitat will be susceptible to different limiting factors, different predators, different energy sources, and different climates. If the new habitat's limiting factors fail to restrict the species' growth, it will continue to multiply, out-competing native organisms for resources, and disrupting the entire ecosystem. Species are sometimes introduced into new habitats through natural factors, like storms, ocean currents, or climate shifts. The majority of invasive species, though, are introduced by humans.

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