Effects of Human Activities on Ecosystems and Environmental Conservation

Lessons

Senior 3 · Biology

Effects of Human Activities on Ecosystems and Environmental Conservation

5 lessons

Lesson 4 of 5

Extinction and the Conservation of Endangered Species

25 min

A species brought back from the brink

In 2008 there were estimated to be about 680 mountain gorillas in the world, all of them in the forests of the Virunga volcanoes (shared by Rwanda, Uganda and the Democratic Republic of the Congo) and Bwindi in Uganda. The subspecies was listed as Critically Endangered. By 2018 the estimate had risen to over 1,000, and the IUCN moved the mountain gorilla to the less severe category Endangered, crediting anti-poaching patrols, veterinary care such as removing snares, cooperation across borders and the support of communities living around the forests. In 2026 the Rwanda Development Board reported over 1,060 mountain gorillas in the wild. Few species recover like this. Most endangered species are still declining, and many have already gone for ever.

Definition

Extinction: the permanent disappearance of a species: no living individual remains anywhere. Local extinction: the disappearance of a species from one area while it survives elsewhere.

Endangered species: a species at high risk of becoming extinct in the wild.

IUCN Red List: the list, kept by the International Union for Conservation of Nature, that places species in categories according to their risk of extinction.

Conservation: the protection and careful management of species and habitats so that they survive.

In-situ conservation: protecting a species in its natural habitat (a national park). Ex-situ conservation: protecting it outside its habitat (a zoo, a botanical garden or a seed bank).

The Red List categories

Figure 1: The IUCN Red List categories, from least to greatest risk.

Why species become extinct

Cause	How it works	Example
Habitat destruction	the species loses food, shelter and breeding sites; the main cause worldwide	forest cleared in Gishwati (Lesson 2)
Over-hunting and poaching	animals are killed faster than they breed; snares also catch other species	rhinos killed for their horn across Africa
Introduced (invasive) species	a new species competes with, eats or infects native species	water hyacinth, a South American plant, choking lakes and rivers in East Africa
Pollution	poisons, low oxygen and plastic kill wildlife	DDT and birds of prey (Lesson 1)
Disease	new pathogens spread, especially in small, crowded populations	diseases caught from people threaten gorillas
Climate change	habitats become too hot, dry or wet for the species	mountain species with nowhere higher to go

Species most at risk are large, slow-breeding animals, species found in only one place, and species whose populations are already small, because a small population can be wiped out by one disease outbreak or bad year and loses genetic variety through inbreeding.

Worked example 1: how fast did the gorillas recover?

Take the IUCN estimates of 680 mountain gorillas in 2008 and 1,000 in 2018. (a) Calculate the percentage increase. (b) Calculate the mean yearly growth rate, assuming steady compound growth.

(a) $\frac{1000 - 680}{680} \times 100\% = \frac{320}{680} \times 100\% = 47\%$ .
(b) Growth over 10 years multiplies the population by $\frac{1000}{680} = 1.47$ . The yearly factor $r$ must satisfy $r^{10} = 1.47$ , so $r = 1.47^{\frac{1}{10}} = 1.039$ The population grew by about 3.9% a year.

Interpretation: a steady 3.9% a year is fast for a large ape that has one baby every few years; it shows that deaths from poaching and snares had been cut sharply.

How endangered species are conserved

Protected areas (in situ). Volcanoes, Nyungwe, Akagera and Gishwati–Mukura national parks protect whole ecosystems, not just one species.
Anti-poaching and veterinary care. Rangers patrol the parks and remove snares; vets treat injured or sick gorillas in the forest.
Benefits for local communities. The Rwanda Development Board reports that 10% of national park tourism revenue is reinvested in communities around the parks. Since 2005 the yearly Kwita Izina ceremony has named the baby gorillas born in the Volcanoes National Park.
Laws. National laws forbid hunting protected animals; international agreements such as CITES control trade in endangered species and their parts.
Ex-situ conservation and reintroduction. Zoos breed endangered animals and seed banks store seeds. Animals can also be returned to the wild. Akagera received lions in 2015 and eastern black rhinos in 2017 and 2019, species that had disappeared from the park; the five black rhinos of 2019 came from zoos in Europe. Southern white rhinos were added in 2021 and 2025.
Education and research: counting populations (Unit 2), studying their needs, and teaching people why they matter.

Worked example 2: sharing the benefits

The Rwanda Development Board reported in 2026 that tourism revenue sharing had supported nearly 1,300 community projects with more than Rwf 23 billion. (a) Estimate the mean amount per project. (b) Suppose a park earns Rwf 4.5 billion from tourism in one year (illustrative figure). How much goes to its communities at 10%? (c) Explain how this helps conservation.

(a) $\frac{23\,000\,000\,000}{1300} \approx 17\,700\,000$ : about Rwf 18 million per project (an estimate, since the report gives "more than" and "nearly").
(b) $0.10 \times 4\,500\,000\,000 = 450\,000\,000$ : Rwf 450 million.
(c) Schools, health centres and water supplies paid for by tourism show people that living animals are worth more than poached ones or cleared land, so communities help protect the park.

Warning

Common mistakes. (1) "Endangered" and "extinct" are not the same: an endangered species can still be saved. (2) Zoos alone cannot save a species; without protected habitat there is nowhere to return it. (3) Moving from Critically Endangered to Endangered does not mean a species is safe: the mountain gorilla is still at high risk.

Rwanda's mountain gorillas: A conservation success story (africanews). Watch for the conservation methods mentioned and the challenges that remain.

Tip

Memory hook: "HIPPO" for the causes of extinction. Habitat loss, Invasive species, Pollution, Population growth (more people using more land) and Over-hunting. Add disease and climate change for full marks.

✦

Practice: extinction and conservation

Distinguish between extinction and local extinction.
Name the three "threatened" IUCN Red List categories in order of increasing risk.
Give four causes of extinction.
Distinguish between in-situ and ex-situ conservation, with one example of each.
A population of an antelope fell from 2,400 to 900 in ten years. Calculate the percentage decrease.
Why are large, slow-breeding animals more at risk of extinction than small, fast-breeding ones?
Explain two ways in which the return of rhinos to Akagera depended on ex-situ conservation or on other countries.
Evaluate this view: "Money spent on protecting gorillas would be better spent on farms."

Show answersHide answers

Extinction is the permanent loss of a species everywhere; local extinction is its loss from one area while it survives elsewhere.
Vulnerable, Endangered, Critically Endangered.
Any four: habitat destruction, over-hunting and poaching, invasive species, pollution, disease, climate change.
In-situ: in the natural habitat, e.g. gorillas protected in Volcanoes National Park. Ex-situ: outside it, e.g. rhinos bred in zoos or seeds in a seed bank.
$\frac{2400 - 900}{2400} \times 100\% = 62.5\%$ .
They produce few young and take a long time to reach breeding age, so they cannot replace losses quickly; they also need large areas of habitat.
The eastern black rhinos of 2019 came from zoos, which had kept and bred them (ex situ). The other rhinos and the lions came from parks in other countries, so the reintroductions depended on international cooperation.
Mostly disagree. Gorilla tourism brings in money, jobs and community projects (10% of park tourism revenue goes to communities), and the forests protect water supplies and soil for the farms below. A balanced answer notes that communities next to parks must share the benefits, or support for conservation falls.

Key points

Extinction is permanent; the IUCN Red List ranks risk from Least Concern to Extinct.
Main causes: habitat destruction, over-hunting, invasive species, pollution, disease and climate change.
Conservation combines protected areas, anti-poaching, community benefits, laws, ex-situ breeding and reintroduction.
The mountain gorilla rose from about 680 (2008) to over 1,000 (2018) and was moved from Critically Endangered to Endangered.

Sources and credits

21.2: Threats to Biodiversity, from Concepts of Biology by Samantha Fowler, Rebecca Roush and James Wise (OpenStax), via LibreTexts Biology, licensed under CC BY 4.0. Adapted by Ganzaa.; 21.3: Preserving Biodiversity, from Concepts of Biology by Samantha Fowler, Rebecca Roush and James Wise (OpenStax), via LibreTexts Biology, licensed under CC BY 4.0. Adapted by Ganzaa.
Mountain gorillas: IUCN, "Fin Whale, Mountain Gorilla recovering thanks to conservation action – IUCN Red List", 14 November 2018; Rwanda Development Board, "Rwanda announces namers for the 21st Kwita Izina gorilla naming ceremony", 2026 (population, Kwita Izina since 2005, revenue sharing).
Akagera reintroductions: "About Akagera National Park", Akagera National Park (African Parks and the Rwanda Development Board); African Parks, "The Return of the Rhino: From Europe to Rwanda" (2019).
Photo: Mountain gorilla (Gorilla beringei beringei) female with baby, Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons.
Video: Rwanda's mountain gorillas: A conservation success Story, africanews, embedded from YouTube.

Written by Ganzaa: Figure 1, the tables, the worked examples and the practice questions.

1A species brought back from the brink

2The Red List categories

3Why species become extinct

4How endangered species are conserved

A species brought back from the brink

The Red List categories

Why species become extinct

How endangered species are conserved