Detecting and Understanding Species Declines and Extinction Paradigms

Video Assignment and Administrative Announcements

• Video Assignment Details: The lecturer has uploaded the video assignment details to the unit site. Due to recent delays, the deadline has been extended to June 3, replacing the original schedule.

• Group Allocation: Students must check their group allocation in the assessment resources section immediately. Groups consist of three or four members, each assigned a distinct group number.

• Contacting Group Members: An Excel file containing the email addresses of all group members is available for download. It is expected that students contact their group members by the end of the week. Response times should be within 48 hours.

• Communication Protocol: If a student does not receive a response after two attempts and an additional 24 hours of waiting, they must contact the lecturer immediately to avoid project delays.

• Feedback Fruits Platform: Peer and self-assessment will be conducted via the Feedback Fruits platform on the unit site. This process is completely anonymous.

• Assessment of Contribution: Contribution scores can affect the final grade.

  • High overall assessment results in no grade adjustment.

  • Failure to complete the self or group assessment may lead to a grade adjustment.

  • Consistently low scores from peers can result in a downward grade adjustment.

  • Fair and even sharing of tasks ensures the grade remains unchanged.

• Assignment Objective: The task involves creating a short video regarding a topical and controversial wildlife issue.

Questions & Discussion

• Nathan: Is only one person submitting the video?

• Lecturer: Yes, that is correct. Only one group member needs to submit the video assignment on behalf of the whole group, and then the entire group will receive a score for that submission.

Ecological Detection of Species Declines

• Ecology in Conservation: Information gathered from ecological studies is used to inform species conservation. When species drive toward extinction, they typically start by declining in geographic range or population size.

• Agents of Decline: Once the ecological requirements of a species are understood (linked to the species' niche concept), researchers can identify possible agents of decline that cause population reduction.

• Hypothesis and Testing: By looking at past and present distributions, researchers construct hypotheses regarding decline. These are then tested experimentally.

  • Example (Predator Control): To test if an invasive predator is causing decline, researchers might implement predator control in one area (manipulation) while maintaining an environmentally identical area without control (the control group). Monitoring these populations over time provides a powerful experimental test.

Rarity vs. Decline

• Natural Rarity: Most species are naturally low in abundance and patchily distributed. Rarity itself does not necessarily indicate a species is in trouble.

• Focus on Rate: Conservationists are concerned with the rate of decline—the consistent and potentially sharp reduction of a population over time—rather than low numbers alone.

• Traits Influencing Vulnerability: Certain traits make species more vulnerable to extinction, though they do not guarantee decline:

  • Low natural numbers.

  • Colonial breeding (breeding only in a few specific locations).

  • Restricted distributions (e.g., specific mountaintops or unique soil types).

Ultimate vs. Proximate Causes of Extinction

• Diagnosis Challenges: In very small populations, it is difficult to distinguish the original cause of decline from the final factor that triggers extinction.

  • Scenario: Habitat fragmentation (the primary problem) isolates populations; an invasive predator then wipes out the remaining individuals (the final extinction event).

• Rapid Declines: Species can disappear extremely quickly. The Christmas Island pipistrelle (a small insectivorous bat) went from widespread abundance to extinction in approximately one decade.

Case Study: The Aloysian Canada Goose

• Background: A subspecies of the Canada goose breeding in the Aloysian Islands (Bering Sea) and wintering in California and Japan.

• Initial Hypothesis: Sharp declines in the 20th century were attributed to egg and gosling predation by Arctic foxes on breeding islands.

• Management Error: Foxes were eliminated from several islands, but the geese numbers did not increase; the decline continued. By 1975, only about 1,000 birds remained.

• True Cause: The actual cause was hunting in the wintering grounds in California and Japan. Once hunting stopped, the population tripled in size.

• Lessons on Migratory Species: Managing migratory species is challenging because efforts in one jurisdiction (e.g., protecting breeding grounds) can be undermined by habitat destruction or hunting in another. This necessitates international conservation agreements (e.g., for turtles or migratory birds).

Mathematical Detection of Decline

• Intrinsic Rate of Increase ($r$): This measures a population's ability to increase. A negative value represents a decline.

• Data Requirements: Ideally, multiple estimates across long durations (days, weeks, or years) are needed to separate natural environmental variation (due to rainfall or resource availability) from true decline.

• Formula for $r$:     $\r = \frac{\ln(n_t) - \ln(n_0)}{t}$

  • $n_0$: Initial population size.

  • $n_t$: Population size at future time $t$.

  • $t$: Time elapsed between sampling.

• Example Calculation: If a population drops from 320 to 95 over 7 years:     $n_0 = 320$     $n_t = 95$     $t = 7$     $r = -0.175$

• Converting to Annual Decline ($d$): To calculate the percentage decline per year:     $d = 1 - e^r$

• Example Result: Using $r = -0.175$:     $d = 0.159$     This represents a 15.9% decline per year, which is considered very high. Anything above 5% or 10% is of great concern to managers.

Statistical Analysis and Bias

• Observer Bias: Human error in visual counts. For example, spotlighting for nocturnal animals depends on the observer's ability. Inconsistent observers can lead to false population estimates.

• Survey Technique Changes: Switching methods (e.g., from cage traps with 30% success to higher-capture camera traps) can suggest a false population increase.

• Linear Regression: Used to fit a line through data points using the equation $y = a + bx$.

  • $R^2$ Value: Assesses the quality of the fit (the closer to 1.0, the better).

  • Non-linear Data: Ecological data is often non-linear (e.g., quadratic/hump-shaped distributions where species favor intermediate temperatures—the "Goldilocks idea").

• Log Transformation: When count data spans from very low to very high (e.g., 2,000 to 20,000), log-transforming the data provides a more accurate trend analysis.

• Example Prediction: For a Caribou population studied between 1961 and 1986:

  • Linear regression on untransformed data predicted extinction by 1984 (which is inaccurate since samples were taken in 1986).

  • Log-transformed data ($R^2 = 0.86$) predicted a much later extinction around 2063.

Small Population Paradigm vs. Declining Population Paradigm

• Graham Cawley: A famous Australian (originally New Zealand) wildlife ecologist who published extensively on these paradigms.

• Small Population Paradigm:

  • Concerned with the consequences of rarity.

  • Focuses on population genetics, dynamics, and stochasticity.

  • Relevant for island populations, captive zoo populations, and isolated mountaintops.

• Declining Population Paradigm:

  • Focused on detecting, diagnosing, and halting the decline itself.

  • Identifies the specific "idiosyncratic" causes (case-specific factors) to prevent populations from becoming small.

Australian Biodiversity and Threats

• Extinction Record: Australia has the world's worst rate of mammal extinction (approximately 40 species lost since European colonization). Overall, more than 100 species and 100 ecological communities are listed as threatened.

• Key Threats:

  • Predation by invasive species (feral cats, foxes).

  • Competition with introduced herbivores (rabbits, goats, deer, buffalo, camels, pigs).

  • Climate Change: The Lemuroid ringtail possum is highly susceptible to heat stress (temperatures in high 30s/low 40s) due to poor thermoregulation.

  • Hunting: Less common in Australia, but impacted the estuarine crocodile (now protected and recovering).

Genetics and the Extinction Vortex

• Stochasticity: Small populations are disproportionately affected by local events (demographic/environmental). A 20% loss in a population of 10 is catastrophic compared to 20% of a million individuals.

• Genetic Drift: The loss of alleles, which occurs when populations are isolated and dispersal is reduced.

• Inbreeding Depression: Small populations lead to mating between close relatives, increasing the expression of semi-lethal recessive alleles.

• The Extinction Vortex: A compounding spiral where lost genetic diversity reduces fertility and increases mortality, making the population smaller, which further increases inbreeding. It is compared to water spiraling faster as it nears a sink drain.

Minimum Viable Population (MVP) and SAFE Index

• Definition of MVP: The fewest number of individuals required for a self-sustaining, viable population. This varies by life history (e.g., elephants vs. mayflies).

• Applications of MVP: Used for national park design and off-reserve conservation on private lands to ensure landscape functionality.

• The 50/500 Rule: A historical rule of thumb suggesting 500 individuals for viability and 50 as a dire threshold for genetic diversity loss. This is now considered too coarse.

• SAFE Index: Developed by Corey Bradshaw, it stands for the ability to forestall extinction. It measures how far a species' current population is from its MVP. A population of 5,001 with an MVP of 5,000 is considered "not safe."