Threats to Biodiversity Lecture Notes

Indirect and Direct Drivers of Biodiversity Change

IPBES Report (2019): Nature is significantly altered by humans, with rapid decline in ecosystems and biodiversity indicators.
Indirect Drivers:
- Shape the environment and give rise to direct drivers
- Demographic and socio-cultural issues related to human population and culture
- Macroeconomic systems, technology development, governance, and conflicts/epidemics
Direct Drivers:
- Land and sea use change
- Direct exploitation of biodiversity
- Climate change
- Pollution
- Invasive alien species
- Infectious diseases
Changes in Ecosystems and Biodiversity:
- Natural ecosystems declined by 47%.
- About 25% of all species are threatened with extinction.
- Around 23% decline in biotic integrity of ecological communities.
- Biomass of wild mammals decreased by 82% since 1970 due to human and livestock population growth.
Other Knowledge Systems:
- A 72% decline in indicators developed by indigenous peoples and local communities, showing deterioration in nature important to them, demonstrating the importance of considering diverse value systems.

Ecosystem Services

Ecosystem processes underpin essential services we get from nature.
- Medicine from plants
- Timber and building materials
- Food and textiles
- Clean water
- Pollination of crops
- Recreation and amenity uses
Decline in biodiversity impacts these services and the sustainability of human population.

The Big Five Threats to Biodiversity

Ecological crisis parallel to the climate crisis
Habitat Disruption:
- Most significant cause historically and currently
- Includes land/sea use change and pollution
Climate Change:
- Currently third most important
- Expected to increase in importance
Overexploitation:
- Overharvesting of goods and services
- Second most important factor
Invasive Alien Species:
- Serious problem, but relatively less important than the top three currently.
Infectious Disease:
- Less important relative to other three.
Impact of drivers varies depending on the level of biological organization (genetic composition, species, populations, community composition, ecosystem processes).
The lecture covers habitat disruption, climate change, and overexploitation; invasive alien species and infectious diseases are covered elsewhere.

Habitat Disruption

Most important factor driving change in nature
Habitat Destruction:
- Conversion of natural habitat to other uses (urban development, industry, farmland).
- Forest clearance is a major aspect.
- Indirect Impact: Fragmentation of habitat.
  - Fragmentation: A contiguous forest area breaking up into smaller fragments over time due to deforestation
    - Initially, the number of fragments increases, but the area of each fragment decreases.
    - Eventually, both the number and area of fragments decline.
    - Resource and population sizes decrease within each fragment.
    - Migration between fragments becomes difficult.
    - The amount of edge habitat increases relative to the area.
Habitat Degradation:
- Habitat remains intact but is modified (pollution, pesticides, acid rain).
Habitat Disturbance:
- Minor, cumulative damage affecting a subset of the population (erosion of paths, damage to coral by divers).

Deforestation of Tropical Rainforests

Deforestation: Conversion of forest to agriculture, facilitated by roads.
Impact on Precipitation:
- Deforestation leads to decreases in precipitation.
- Authors estimated how deforestation drives change in rainfall in tropical regions using satellite observations and mathematical modeling.
- Each percentage point change in forest cover from deforestation alters rainfall per month.
- Almost all regions studied demonstrate negative change in precipitation with increased deforestation.
- Example: The Congo could experience an 8-10% reduction in precipitation by 2100 if deforestation continues at current rates.

Insecticide Use & Neonicotinoids

Insecticide use dates back 2000 years, initially with natural plant extracts.
Neonicotinoids: A family of synthetic chemical pesticides (e.g., Imidacloprid).
- Neurotoxin for invertebrates.
- Systemic treatment for plants.
- Applied as a seed dressing initially, but problematically only about 5% of the pesticide goes into the plant
- 8,000 to 10,000 times more potent than natural insecticides.
- The rest remains in the soil or dissolves in water.
- Experimental studies showed that neonicotinoids significantly impact invertebrate colonies.
- Bumblebee nests smaller, up to 85% reduction in reproductive individuals (new queens).
- Neonicotinoids get into non-target plants in field margins, affecting other invertebrates.
- Identified as a major driver in the decline of insect biodiversity globally.
- Self-regulation of compounds is problematic (conflict of interest).
In the UK, neonics are still used on sugar beet crops, but otherwise they're banned for use in the UK agriculturally in other parts of the world they're still in use and you can find them everywhere.

Overexploitation

Unsustainable harvesting of goods and services from nature.
- Examples: Changing or eradication of megafauna, exploitation of whale and fish stocks.
Nature valued for food, medicine, industrial materials, and recreation.
Resource value increases as it becomes rare, driving demand.
- African elephants & ivory prices: In 1969, the global cost of ivory was $2.5 per pound$ . By 1989, that had increased to $90 per pound$ . At the same time, the resource decreased markedly from 1.3 million elephants down to just above half a million elephants.

Fisheries Overexploitation

Capture production (nets, trawling) is unsustainable, exceeding 80 million tons per year.
Tipping points can drive an ecosystem into a new stable (non-productive) state.
- German fishery: Before 1995 capture rates increased markedly up to a peak, then after around 1997, capture rates began an precipitous decline down to below 5000 tons per year.
- Decline due to reduction in catchable fish abundance.
- Reproductive capacity of fish population compromised.
- Spawning stock biomass fell below where reproduction is impaired, and stayed there even with decreased fishing.
- The population could not recover
- Models underestimated the amount of spawning stock biomass, because they didn't factor in these tipping points.
- Climate change further locked the population into a lower density, less productive state.

Climate Change

Impacts nature at different levels of the biological hierarchy.
Individual/Population Level Processes:
- Phenotypic plasticity: Plastic change in an organism's phenotype within a single individual.
- Evolution: Climate change can drive the evolution of populations.
Demographic Effects: Geographical ranges can shift as individuals move to track climate.
Community Effects:
- Species adapted to the new climate will do better, and species that are poorly adapted do less well.
- Sorting or turnover of species within communities.
- New species can enter as climate becomes suitable.
Impacts on ecosystem processes and services.

Migration

Example: The speckled wood butterfly saw huge range expansion in the UK from south to north as climate warmed.
If migration doesn't happen: species ranges decline as the climate shifts and only some parts of the range remain suitable.
With migration: individuals can colonize new landscape patches, moving towards the poles, retaining similar numbers.
Study by Hickling et al. showed a nearly uniform northward distribution shift of animal species in the British Isles.

Species Distribution Modeling

Taking species current distributions, environmental factors, and then predicting what the new distribution will be.
Potential problems with models: All informative data can still produce similar results or similar predictions; Have to use these models carefully.

Adaptive Phenotypic Plasticity

Individual Level Effects
Great Tit Example: the egg laying date for this species has decreased through time, in relation to the amount of warmth the sun is giving in a particular year.
Individual birds adjust laying date depending on thermal conditions.

Evolution

Tawny Owl Example: Tawn Owls exist in two different forms: a grey form on the left and a brown form on the right.
There existed a genetic advantage to being the grey form, where they were camouflaged in the snow.
Decreased Snow Depth over time has resulted in a selection for Brown Wolfs, since the camouflage is unnecessary, leading to a change in genetic frequency of the owl populations.
There have been evolutionary studies in adaptation to drought in plant species, driving for selection of early flowering time.
Many Populations are adapting, whether through evolution or plastic changes, but the key question is whether it can outpace current climate change.

Traits

Biological trait or a functional trait is a specific functional activity carried out, um, by the organism that influences its response to the environment.
Can measure the trait of a plan (the amount of camp height that can be produced); relationship between species with a high growth potential doing better during warming

Threats to Biodiversity

Every week, we face a three, six, nine world with moving towards three degrees of warming towards the sixth mass extinction and towards a significantly greater human population.
The overarching driver of species extinction is human population growth and increasing per capita consumption.
Species extinction rates are 100-1000 greater than background extinction rates, and are expected to increase tenfold in the future.

Estimating Species Richness

Need to know the number of species before assessing losses.
Erwin's experiment (insecticides on tree canopies): Extrapolation is common to all estimates of species richness at the global scale (cannot simply document all species because resources don't exist)
Jennifer Irwin: A Tiny Garden in Leicestershire with over 2500 species, 4 of which were new to science.

Bacteria

Even more diversity (larger scale than obvious species such as animals/plants).
100g of soil contain around 10 billion bacterial cells.
4-5000 species per gram.
Global species richness is possibly up to a billion globally.

New Species Discoveries

Examples: Three-toed pygmy sloth, Solomon Islands bats
400 Mammals discovered since 1993

Quantifying Global Biodiversity

Rely on extrapolation (cannot document all species).
Macroecological patterns (Body Size)
Latitudinal gradients (Generally species greatest in the tropics)
Diversity Ratio Approach
- Calculating the ratio of taxon number between two taxonomic groups:
- Calculating Ratio of Fungi to Plants
  - $Fungi/Plants = 277/48 = 5.77$
- Using the calculated number to extrapolate the number of Species:
  - $270,000 plants * 5.77 = 1.56 million species$

Early Estimates of Global Biodiversity

Key taxonomic species (Insects are going to be the most species rich group, most of them remain unnamed).
From that, it can be determined that there are 8.7 million eukaryotic species globally (margin of error $\pm 1.3$ million).
The estimates come from different taxa using discovered rate over time

Causes for Caution

Does not include bacteria.
Very important for ecosystem processes and services.

Biodiversity Enumeration

Diversity ratio approach. Allows for estimation in a poorly categorized group in comparison to a well characterized group.

Factors Related to Areas

Generally Larger Areas have more Species.
Species area relationship is a very general rule for ecology (More species when more area).
- $log \text{ of species number} = z * log \text{ of area} + \text{ a constant}$
- Reduce an area to 10% of original size, expect to lose 50% of their species.

Biodiversity Hotspots

Areas with very high levels of biodiversity.
1980's Norman Myers created a list of 10 forest hotspots (updated in 2004 with 34 hotspots).
Criteria: At least 1500 species or have lost more than 30% of its habitat.
Prioritizing resources will save the greatest number of species at the lowest economic costs.
Mediterranean Basis/Tropical Areas.
Areas where there is high nitrate deposition means lower plant species richness.

Extinction

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) estimates around a quarter of all species are threatened by extinction.
Specific Groups (cycads, amphibians) are particularly threatened for extinction.
A range of increasing populations that will likely see extinction.
There is a human impact involved that endangers key factors of species.
Many Species go extinct before there is a chance for species to be discovered.

Calculation of extinction rates

Measured in species per million species years.
Calculating extinction rates involves dividing the observed extinctions by the opportunity for extinction.
- Calculating the opportunity for Extinction:
  $Number of taxa * 100$ \n* Multiplying that by a million gets to 106. Thus, in a million years, we'd expect to see 106 extinctions in this group. So, that's the estimated extinction rate.

Taxonomic vs Extinction Rate over Time

Pre-1900 vs Post 1900 is often double.
Rates of extinctions have lead people to speculate that we're within another major extinction.
Many species are already involved within an extinction, and there is likely going to be an area of pivotal role that drives extinction.
Future Extinction Rate: up to 10,000 more greater than base rates. This is currently 100 to 1,000. Overall a high increase caused in the activities by people.