Threats to Biodiversity and Taxonomic Knowledge Gaps

Defining Threats to Biodiversity and Species Persistence

• Definition of Threats: Activities that directly or indirectly impinge on the viability and survival of a species population.

  • Direct Threats: Immediate impacts such as poaching and hunting.

  • Indirect Threats: Secondary impacts such as pollution or climate change that affect the environment the species relies upon.

• Concept of Persistence: In conservation, persistence refers to a species maintaining a viable breeding population over the long term. Short-term survival (e.g., 20 years before extinction) is not considered persistence.

• Sustainability vs. Threat: Hunting and poaching are only considered threats to biodiversity if they affect the viability of a population. Ironically, sustainable poaching or hunting can exist if it does not impair long-term population viability.

• Role of Extinction: Extinction is a natural process that has occurred throughout Earth's history without human intervention. Concern primarily arises when human activities—direct (poaching) or indirect (pollution, climate change)—become the drivers of extinction.

• Categorization Challenges: There is no universal standard for categorizing threats, as different disciplines—ecologists, conservation biologists, and population ecologists—use different terminology based on cultural or local contexts (e.g., viewing human-elephant relations as conflict vs. interaction).

Quantitative Dynamics of Threats: Exposure and Intensity

• Exposure: Refers to the degree to which an organism or population is subjected to a threat.

  • High-value, rare specimens like certain cacti or orchids have high exposure due to collector demand. Mature cacti may be $100$ years old and belong to genera with limited ranges, making them highly vulnerable to extinction in the wild.

  • Cultural norms drive specific exposures, such as German interest in rare orchids and cacti, or Japanese interest in rare beetles.

• Intensity: The magnitude of the threatening process.

  • In fishing, bycatch probability might be low on a per-trawler basis, but as the intensity of trawling (number of ships) increases, the total impact on bycatch species becomes severe.

• Tempo of Impact:

  • Events: Sudden, high-impact incidents like oil spills. While the initial event is rapid, the impact decays over decades as the oil decomposes, signifying an ongoing presence in the system.

  • Long-term Processes: Phenomena like climate change that have a cumulative, increasing probability of causing extinction over time.

Invasive Species and Trophic Interactions

• Rats as Invasive Species: Humans have transported various rat species globally, primarily via seafaring:

  • Black Rat (Rattus rattus): Distributed by more recent seafarers ($500$ years).

  • Brown Rat (Rattus norvegicus): Also distributed by recent seafarers.

  • Pacific Rat (Rattus exulans): Transported by Polynesian seafarers on canoes.

• System Vulnerability: In mainland Australia, these rats have lower impact because the system contains indigenous rats. On islands (e.g., Lord Howe Island), where there are no indigenous land mammals except bats, invasive rats have high impacts by eating birds, eggs, insects, and fruits.

• Case Study: Lord Howe Island (1918):

  • A ship ran aground in 1918, introducing black rats.

  • The Lord Howe stick insect was thought extinct because rats consumed them. It was rediscovered on Ball's Pyramid, a steep, uninhabited pyramid-shaped island nearby that remained rat-free.

  • Rat Eradication Program: A recent, successful program involved spreading rodenticide across the island using helicopters and $28,000$ bait stations. A total of $1.2\,kg$ of poison was used for the entire island. Consequently, species thought extinct for over $100$ years have begun to return.

• Trophic Cascades (Macquarie Island): Initially, cats were shot to protect birds, but this led to a population explosion of rabbits because the cats were no longer predating them. The rabbits then destroyed the native vegetation.

Habitat Destruction and Degradation

• Destruction vs. Degradation:

  • Destruction: Complete clearing, such as replacing forests with agriculture.

  • Degradation: Reducing habitat quality, such as selective logging or fragmentation into small patches.

• Fragmentation Effects: Small forest patches experience "decay" at the margins because they are exposed to wind, dryness, and drought. The interior cores lose the protection of the surrounding canopy.

• Invasive Native Species: Habitat degradation can involve native species becoming over-abundant due to human-altered regimes.

  • Example: Sweet Pittosporum (Pittosporum undulatum) is native to Eastern Victoria but is invading forests around Melbourne (e.g., Eurala Nature Reserve in Trafalgar) because fire has been suppressed. It creates dense shade that kills ground-dwelling plants and animals adapted to open dry sclerophyll forests.

• Trampling Experiment:

  • An experiment on beaches measured the impact of human steps ($0$ to $60$ per square meter).

  • Results showed that increased trampling significantly reduced both the abundance of organisms (mostly invertebrates living in the sand) and the number of species.

  • This degrades the habitat for shorebirds that rely on those organisms for food.

Overexploitation and Pollution

• Atlantic Cod Fishery: A historical example where harvests grew from $100,000$–$200,000$ tons to over $800,000$ tons by 1950 before crashing to near-zero. The species is not extinct but is "commercially unviable."

• Bushmeat: A significant conservation issue; $70\%$ of mammal species in Africa are hunted for food. This raises ethical questions regarding the rights of indigenous people to hunt species that may be threatened.

• Illicit Trade: An online trade involving nearly $3,000$ species, many listed under CITES (Convention on International Trade in Endangered Species). Reptiles are frequently smuggled in suitcases or socks.

• Urban Pollution:

  • Gardner's Creek: A channelized, straightened creek that used to wind through the landscape. It is now a cement drain in sections (e.g., towards Warrigal Road).

  • Pollutants: Include lead ($Pb$) from old petrol, fertilizers (phosphorus $P$, nitrogen $N$, potassium $K$) causing eutrophication, and pharmaceuticals/viruses detected in stormwater.

• Plastic Pollution: Approximately $8,000,000$ tons of plastic enters the ocean annually. Large plastic items break down into microplastics, which are ingested by seabirds like shearwaters. A single bird's stomach can be found filled entirely with plastic bits that look like fish.

The Seven Impediments to Conservation

• The Taxonomic Bias: Records are heavily biased toward "sexy" or charismatic species.

  • In iNaturalist, $26\%$ of $107,000$ beetle records belong to just $7$ colorful species of ladybirds (Coccinellidae), while $95\%$ of ladybirds are small, brown, and ignored.

  • Bird Data: On average, each of the $830$ breeding bird species in Australia has $110,000$ records in the Atlas of Living Australia (ALA).

  • Insects: For the $250,000$ insect species, the average is only $22$ records per species, with many having zero.

• Knowledge Shortfalls:

  • Linnaean Shortfall: The gap between described species and those that exist. $95\%$ of species are unknown. It is estimated that between $1,500$ and $56,000$ non-marine invertebrate extinctions have occurred in Australia unnoticed.

  • Wallaceian Shortfall: The lack of knowledge regarding the geographic distribution of species. Records are clustered around cities and roads (e.g., Melbourne, Sydney, Brisbane).

  • Prestonian Shortfall: The lack of data on population trends and patterns over time.

  • Hutchinsonian Shortfall: The lack of knowledge regarding the ecology, functional roles, and species interactions (predators/parasites) of organisms.

Short Range Endemics (SREs)

• Definition: Species with naturally small, restricted geographic ranges, often limited by poor dispersal abilities.

• Dispersal Mechanisms:

  • Spiders: Often disperse via "parachuting" or ballooning on silk, leading to wider distributions.

  • Mites and Millipedes: Poor dispersers that do not fly or parachute. In the Australian Alps, species are often restricted to single mountain peaks.

• Evolutionary Context: Australia's drying climate since the Miocene has restricted wet-forest taxa to montane "islands" (Otways, Dandenongs, Mount Macedon), driving the evolution of unique species in each upland region.

• Examples:

  • Dibolagonus (millipedes): High diversity in the Alps; identified via male genitalia (gonopods).

  • Lesothes (beetles): Charismatic but poorly known; species count in Victoria doubled in two years of focused study.

  • Victoraphanta atramentaria (Carnivorous snail): Divided into four species across Victoria and Tasmania.

Future Conservation Strategies

• Need for Baseline Data: The Herman Slade Foundation project (surveying $54$ sites) was the first baseline invertebrate survey in the Australian Alps.

• Protecting Places, Not Just Species: Since $90\%$ of invertebrates are undescribed and cannot be legally listed, the best strategy is to protect high-biodiversity habitats ("hotspots of richness").

• Modern Tools: DNA barcoding (sequencing the $CO1$ gene) allows researchers to differentiate species rapidly without needing exhaustive taxonomic descriptions first.

• State of the Environment Report (2021): Identifies monitoring deficiencies as a fundamental barrier to determining if conservation actions are effective.

Questions & Discussion

• Question (Student): How do you report sightings of Rakali (Water Rats, Hydromys chrysogaster) in the local area?

• Response (Professor): Report them on iNaturalist. They are mobile and have been seen on the glass bridge near campus. They are distinctive due to the white tip on their tail. While they were common a few months ago, sightings fluctuate.

• Question (Student): How do you name a new species?

• Response (Professor): It involves describing what is distinctive (e.g., using scanning electron micrographs of gonopods), publishing the findings in a journal, and undergoing peer review. While it requires specialist knowledge, discovering new species in leaf litter is relatively easy because so few people look for them.

• Logistics Note: Students wishing to change their workshop times (e.g., from Friday to Tuesday) should email the professor. The identifying guide can be used during practical assessments.