Lesson #6 - Threats to Biodiversity

Mass Extinctions

• Over the course of Earth's history, organisms have experienced large-scale, global die-offs

• When A LOT of species die out in a short time

  • >50% of species

  • 1-2 million years

• Wipe species out more or less at random

• Caused by extremely unusual, short-term environmental changes

Table Showing Earth’s 5 Major Mass Extinctions

If all Biological Niches are occupied…How could new ecological opportunities emerge?

• Mass extinctions reset ecosystems and open ecological niches, providing the opportunity for surviving species to diversify and adapt.

• Ex: Open up niches

Are we in a mass extinction now?

• Loss of species is between 1000 and 10,000 times higher than the natural extinction rate

• Many more species are at risk of extinction (46,000!)

• Average wildlife populations declined by 73% in just 50 years

Why is this happening…Human Alterations!

• Human alterations push species outside their fundamental niches or shrink their realized niches, leading to declines or extinction

• Fundamental niche

  • The full set of environmental conditions and resources a species could use in the absence of competitors and threats.

• Range of tolerance

  • The limits of environmental conditions (e.g., temperature, moisture, nutrients) within which a species can survive, grow, and reproduce.

• Realized niche

  • The narrower portion of the fundamental niche that a species actually occupies due to competition, predation, and other biotic interactions.

What are five ways humans are contributing to population declines?

• Habitat loss

  • The destruction or conversion of natural environments reduces the space and resources species need to survive.

• Invasive species

  • Non-native species establish and spread, disrupting ecosystems by outcompeting or preying on native species or altering their environment.

• Climate change

  • Shifts in temperature, precipitation, and extreme events alter conditions faster than many species can adapt.

• Overexploitation

  • Species decline when humans harvest, hunt, or fish them faster than they can reproduce.

• Pollution

  • Harmful substances released into air, water, or soil degrade habitats and directly harm organisms.

Habitat Fragmentation

• Large, continuous habitats are broken into smaller, isolated pieces that limit movement and increase vulnerability.

• One primary consequence of fragmentation is that it causes a large increase in the amount of "edge" habitat relative to the amount of "interior" habitat. After fragmentation occurs, trees that end up on a forest edge are exposed to intense sunlight and high winds.

• Fragmentation also reduces gene flow, or mixing of genetic information, in many or most of the species present.

What are small populations considered?

• Considered vulnerable

• Vulnerable to random events

  • “Density-independent factors”

• Harder to find mates or colonize new habitat

  • Reduced growth rates

• May get trapped in poor habitat

  • Reduced growth rates and lower carrying capacity

What are small populations considered? (Continued…3 more points)

• Increased genetic drift

  • Reduces genetic variation

• Increased inbreeding + inbreeding depression

  • Increases homozygosity

• Reduced average fitness

  • Less variation, which is a necessary ingredient for natural selection

Summary/Relation Slide

The Dangers of Inbreeding

• Inbreeding is defined as mating between relatives, and that it is considered a form of non-random mating

• Increases genetic homozygosity!

• Can increase frequency of homozygous recessive genotypes with deleterious effects

Another Summary/Relation Slide

Extinction Vortex

• As a population shrinks, it loses genetic diversity. This makes the group less healthy and less able to adapt to changes, which causes the population to shrink even further

• Genetic Drift: In small groups, "bad" genetic traits can become common purely by chance, while helpful traits are lost.

• Inbreeding: With fewer mates available, related individuals breed more often. This leads to inbreeding depression, resulting in lower fertility and higher infant mortality.

• Demographic Variation: In a tiny population, a random event—like a year where only males happen to be born—can be enough to end the entire lineage.

• Environmental Shocks: A small group is much more vulnerable to a single "bad day," like a forest fire or a disease outbreak, which a larger population could survive.

• Consider: When one species enters an extinction vortex...it can impact others!

How can the extinction vortex help us prevent population declines?

• Environment

  • Improve habitat quality to increase carrying capacity

  • Increase habitat area to increase population size

  • Restore connectivity to increase movement and colonization

• Genetics

  • Increase gene flow to decrease inbreeding and reduce homozygosity

  • Decreased homozygosity increases fitness

  • Increased population sizes minimizes the impacts of genetic drift

Vancouver Island marmot Conservation efforts

• Captive breeding programs

  • Matings focus on maximizing genetic variation (genetic screening, avoid inbreeding, etc.)

• Captivity intentionally designed to maximize successful release into wild

• Strategic release to:

  • Increase population sizes

  • Increase gene flow

  • Decrease inbreeding

• An estimated 427 Vancouver Island Marmots in 35 colonies as of Fall 2025! Started with fewer than 30 marmots in 2-3 colonies alive in 2003

How does Conservation Work?

• Protect areas

• Sustainable resource management

• Re-establish species

• Captive breeding and species recovery programs

• Conservation policy and global cooperation

How is Conservation a Science?

• Science is both

• 1. A collection of knowledge, and

• 2. A process for the collection of knowledge.

• The scientific method

  • Ongoing!

• Conservation biology helps us understand and address challenges like the conservation of biodiversity