Comprehensive Lecture Notes on Conservation Biology, Species Extinction, and Biodiversity

Factors Contributing to Species Extinction and Genetic Bottlenecks

• Definition of Official Extinction: A species is declared officially extinct when no more wild specimens remain.
• Rhino Population and Poaching:
      - Motivation for Poaching: Rhinos are hunted primarily for their horns.
      - Misconceptions and Uses: Some believe horns are used for decorative purposes or items like chopsticks (frequently confused with elephant ivory). However, a significant driver is traditional medicine.
      - Scientific Reality of Rhino Horns: There is no scientific evidence supporting the medicinal value of rhino horns. Chemically, the horn is composed entirely of keratin, the same protein found in human fingernails.
• Demographics and Population Viability:
      - Total numbers can be misleading. To understand a species' survival chances, one must look at sex ratios (males vs. females) and age structures.
      - Example Scenario: If a population has $30$ individuals but half are too old to breed, the effective population size is only $15$.
• The Bottleneck Effect in Cheetahs:
      - Cheetahs suffered a genetic bottleneck thousands of years ago, which severely reduced their genetic diversity.
      - Modern cheetahs still suffer from the inbreeding effects of that ancient event.
      - Current threats compounding this genetic fragility include poaching, health issues, habitat loss, and the illegal pet trade.
      - Pet Trade Impacts: Cheetahs are delicate animals and do not survive well in captivity unless handled by zoo professionals.
• Tiger Conservation and Spatial Distribution:
      - Historical Poaching: Tigers were historically hunted for fur (pelts) or for taxidermy (stuffed specimens).
      - Mating Challenges: Low population numbers create a "spread out" effect. If reproductive-age males and females are too far apart geographically, the probability of them finding one another to mate is extremely low.

Case Studies in Avian Extinction and Poisoning

• The Ivory-Billed Woodpecker:
      - Habitat Requirements: They require specific environments with trees, specifically older trees.
      - Drivers of Decline: Massive deforestation is the primary cause of their struggle.
      - Comparison: It is physically similar to the Pileated Woodpecker, which is also a large species.
      - Extinction Timeline: Scientists thought it was extinct by the $1940s$. There is a formal process for declaring extinction where a species must go unseen for a specific number of years.
      - Recent History: There were reported sightings a few years ago that caused excitement, but researchers could not confirm them. The U.S. officially declared the Ivory-Billed Woodpecker extinct approximately $2$ to $3$ years ago.
• California Condors and Lead Poisoning:
      - Scavenging Hazards: Condors are scavengers that eat carcasses. They suffer from lead poisoning because the carcasses they consume often contain lead fragments from ammunition used by hunters.
      - Captivity Challenges: Taking wild animals into captivity for protection is difficult. Some animals cannot handle the stress; one instance involved an animal having a heart attack and dying upon being captured.

Conservation Strategies: Captive Breeding and Reintroduction

• Captive Breeding Programs:
      - California Condors were extinct in the wild when a captive breeding program began. Since the $1990s$, they have been reintroduced.
      - Institutions like the LA Zoo (Los Angeles Zoo) are actively involved in these programs.
      - Current wild population: Over $300$ individuals.
• Reintroduction and Behavioral Training:
      - Reintroduced species often need to be taught how to survive.
      - Learning to Hunt: Initial condor releases failed because the birds were not good at finding dead animals. Reintroduction teams had to place carcasses in the wild to help them find food.
      - Avoiding Human Imprinting: To prevent birds from becoming comfortable with humans, handlers use "condor puppets" to feed chicks. This ensures the babies see a "mom" figure rather than a human, maintaining their natural fear of people.
      - Teaching Migration: Some species, like cranes, have been taught to migrate by following ultralight aircraft.
• Professional Responsibility: Conservationists are often in charge of the last remaining organisms of a species on the planet, a role with immense responsibility.

Environmental Health Indicators and Historical Extinctions

• Indicator Species:
      - These are species that scientists monitor because they provide early warnings of environmental degradation.
      - Amphibians: $41\%$ of amphibians are at risk of extinction according to the IUCN Red List.
      - Sensitivity: Unlike amniotes, amphibians have clear, jelly-like eggs without shells, making them highly susceptible to radiation, climate change, and drought.
      - Scientific Legacy: This field was heavily influenced by David Wake, a famous evolutionary biologist at Berkeley.
• Historical Case Studies of Extinction:
      - The Great Auk: A flightless bird hunted to extinction for meat, fat, and feathers. They were also collected by wealthy individuals for private collections. The last two individuals (a male and female) were killed on an island while tending to an egg, which was crushed during the encounter.
      - The Heath Hen: Similar to a chicken. They were hunted heavily, and the last population on Martha’s Vineyard was wiped out by a fire.
      - The Passenger Pigeon: Once the most numerous birds (billions). Flocks took hours to pass. Because they were so common, people in the $1800s$ believed the supply was inexhaustible and killed thousands daily. The last passenger pigeon, named Martha, died in a zoo.
• The Bison (American Buffalo):
      - Once numbered in the tens of millions. They were nearly hunted to extinction due to a lack of conservation concepts and conflicts with cattle ranching.
      - Land Rights Issues: Under the Trump administration, policies were proposed to keep bison off government land (which accounts for $50\%$ of land ownership), potentially restricting them to private property.

Biodiversity Hotspots and Invasive Species (The HIPPO Model)

• Biodiversity Hotspots:
      - Areas defined by high biodiversity, high numbers of endemic species (found nowhere else), and high levels of threat.
      - The Cloud Forest: Located at higher elevations than tropical rainforests. It is cooler and home to the Spectacled Bear (the only bear in South America), which is endangered due to habitat loss.
• Invasive Species (The "I" in HIPPO):
      - Invasive vs. Introduced: An introducted species becomes "invasive" when it outcompetes and harms native species.
      - The Brown Tree Snake: Introduced to Guam accidentally via the landing gear of airplanes. These tree-climbing snakes have caused significant local extinctions.
      - Kudzu: A fast-growing vine from Asia that chokes out forests in the U.S. by blocking sunlight.
      - Other Examples: Fire ants and the Pepper Tree (found on campus).
      - Cultural Reference: The Simpsons episode where the family goes to Australia and sees a swath of green frogs (Cane Toads) destroying the landscape illustrates the invasive species problem.

Questions & Discussion

• Question Regarding Rhino Horns: "And why do people want their horns? To make it into chopsticks?"
      - Response: The speaker clarified that while decorative use (like chopsticks) exists, it is often confused with elephants. The main reason is traditional medicine, despite the fact that rhino horn is $\text{keratin}$ and has no proven medicinal value.
• Question Regarding Tigers: "Anybody know why? Why are we killing tigers? Is it for the fur?"
      - Response: Historically it was for fur and pelts, and sometimes for decoration/taxidermy, but low population density makes it difficult for them to find mates today.
• Question Regarding Condor Puppets: "Who's feeding it? The mom?"
      - Response: A handler's hand is feeding the baby using a long condor puppet so the bird doesn't get comfortable with humans.
• Audience Anecdote on Bears: A student shared that they saw a bear trap while hiking.
      - Response: The instructor noted that grizzlies (Brown Bears) need massive amounts of land. While they currently live in Alaska, their historical range covered most of the Western U.S. There is a debate among scientists about reintroducing them to California versus the potential for human-grizzly conflict.