Lecture 10 - Narrow Range Endemism in Terrestrial Invertebrates
Introduction to Narrow Range Endemism in Terrestrial Invertebrates
The study of narrow range endemism in terrestrial invertebrates is considered one of the final frontiers for understanding biodiversity conservation, particularly in Australia and globally.
Many of these invertebrate groups are relatively poorly known compared to better-studied organisms like birds, mammals, or plants.
Nick Porch identifies this field as crucial for protecting biodiversity because invertebrates represent the vast majority of species on Earth.
Global Patterns and the Example of Hawaiian Land Snails
Alan Solem provided an estimate in the 1990s regarding land snail diversity in Hawaii.
Of the almost species of snails that previously lived in Hawaii, only to were estimated to still be living.
This implies an extinction rate of approximately for Hawaiian land snails.
This pattern is repeated on oceanic islands worldwide; land snails are among the most threatened groups on the planet due to their island-bound distributions.
The Scientific Reality of Biodiversity: The "Insect Planet"
Robert May (who passed away in 2020) famously remarked that if an alien visited Earth, they would conclude that every species was an insect.
At the level of taxonomic diversity, insects, arachnids, mollusks, and crustaceans constitute the largest portion of biodiversity.
Significant diversity is concentrated in mega-diverse regions like Australia and specifically the tropics, where vast numbers of species remain unknown to science.
Knowledge Bias and the Taxonomic Impediment
There is a significant knowledge bias in conservation data regarding taxonomy and distribution.
Vertebrates (birds and mammals) and flowering plants are "massively oversampled" relative to their actual abundance and diversity.
Terrestrial invertebrates (insects, spiders, gastropods) are "massively undersampled" and have very few occurrence records in existing datasets.
Research distribution is often driven by human interest in "charismatic" vertebrates rather than ecological necessity.
While invertebrates dominate in total described species, and would appear as the overwhelming majority if undescribed species were included, conservation literature focuses disproportionately on vertebrates.
In the literature, vertebrates receive research attention far beyond their proportional diversity, while many invertebrate species have zero dedicated research papers.
Case Study: The 2019–2020 Australian Bushfires
A large percentage of forest in Southeastern Australia (East of Melbourne to Sydney) was impacted by the 2019–2020 fires.
Over of the forest along the coastal escarpment from East Gippsland through the New South Wales coast was burnt.
Governments responded by setting impact thresholds (e.g., species with over of their range burnt) to determine conservation priorities.
While data for vertebrates and plants allowed for distribution modeling and overlay with fire polygons, such data was largely non-existent for invertebrates.
Priority lists created by federal and state governments often included few or no invertebrate species, despite many being significantly impacted.
Regional Data Gaps: The Victorian Context
In Victoria, the government maintains the Victorian Biodiversity Atlas (VBA), which includes extensive data on plants, mammals, frogs, lizards, and birds.
For terrestrial invertebrates, the VBA holds almost no data except for the few species officially listed on the threatened species list.
There is currently no comprehensive checklist of terrestrial invertebrate species for the state of Victoria.
Academic disparity exacerbates this gap: In the School of Life and Environmental Sciences, there are dozens of vertebrate researchers but only one or two dedicated invertebrate researchers.
Conservation Characteristics of Terrestrial Invertebrates
Invertebrates use landscapes differently than other organisms, often residing in high densities within small areas.
A single square meter of leaf litter may contain thousands to over individual animals belonging to hundreds of species.
Characteristics that increase extinction risk include:
Short annual life cycles.
Transitions in ecology (e.g., aquatic larvae and terrestrial adults).
Adults that are only active for brief periods (e.g., two weeks in summer).
Highly specific habitat requirements (e.g., oxygenated, rapidly falling water).
Rapid responses to environmental changes (pollution, fire).
High rates of species turnover along habitat gradients.
Poor dispersal capabilities compared to many vertebrates.
Defining Narrow Range Endemism (NRE)
Endemism is the restriction of a taxonomic group (species, genus, family) to a defined geographic location (island, country, or region).
Narrow Range Endemics (NRE), also called Short Range Endemics (SRE), are typically defined as species having a total geographic range of less than .
This area is equivalent to a square measuring .
While some vertebrates are NREs (e.g., the Baw Baw frog, ), the vast majority of NREs are poorly known invertebrate species.
Biogeographic Hotspots in Victoria
Significant areas for NRE invertebrates in Victoria include:
The Central Highlands (home to Leadbeater's possum).
The Otway Ranges.
The Grampians.
The Western Uplands (Ballarat to the Grampians).
The Promontory and South Gippsland Highlands.
The Errinundra Plateau and East Gippsland.
Montane regions and high plains in the Alps (Mount Buffalo, Hotham High Plains).
Many of these hotspots overlapped significantly with the 2019–2020 fire zones (specifically the Alps and East Gippsland).
The Otway Ranges Example
The Otway Ranges are a relatively small patch of upland wet forest isolated by surrounding lowland cleared habitat or dry sclerophyll forest.
The ranges contain high invertebrate endemism but zero endemic vertebrate species and zero endemic plant species.
Relying solely on vertebrate or plant data (like the VBA) suggests the Otways are uninteresting, yet they host at least known endemic invertebrate species.
Endemic species in the Otways include:
Otway's black snail (genus ).
Otway's assassin spider.
Various undescribed velvet worms (Onycophorans).
Unique endemic genera of beetles and bugs.
Saproxylic Habitats and Micro-habits
Saproxylic habitats (dead and decaying wood) are essential for many NREs.
In forests like the Mountain Ash forests, complex habitats are created by mossy tree trunks, bark, and logs at different stages of decay.
These habitats are highly sensitive to fire, long-term drying, and climate change.
Key groups in these habitats include:
Moromorphine beetles: A Southern Gondwanan group that inhabits dead rotten wood.
Acanthoneura springtails: Large (), colorful, charismatic invertebrates associated with wet wood and slime molds. Most Victorian species remain undescribed.
The Velvet Worm (Onycophora) Case Study
Velvet worms are a primitive group of organisms that terrestrialized approximately million years ago.
They are typically NREs with large genetic differences between species.
There are two families worldwide: one in the northern hemisphere and the southern family (Peripatopsidae).
Eastern and Western Australian groups separated approximately million years ago (during the Cretaceous).
During the 2019–2020 fires, the type localities for numerous velvet worm species (e.g., , , , , ) were entirely burnt.
Despite of their known range being incinerated, none of these species were listed on federal or state priority conservation lists due to lack of awareness/data.
Taxonomic Impediment and New Species Discovery
Nick Porch discusses a personal example: a beetle discovered in the Gippsland Highlands during his youth was only identified as a new species decades later.
This beetle belongs to a complex where four species are described and three to five species remain undescribed.
These species divide habitats into tiny regions: separate species are found in the Dandenong Ranges, Mount Baw Baw, Mount Donna Buang, Toolangi, and the Brighty Mountains.
Future Foundations for Invertebrate Conservation
Effective conservation requires shifting focus toward preserving "significant places" rather than just individual known species.
By identifying regions with high shared evolutionary history and recurring patterns of endemism (like the Otways or Errinundra), researchers can focus efforts where they are most likely to protect unknown diversity.
To improve future responses to environmental disasters (like fires), taxonomic and distributional knowledge must be increased through targeted research.