Lecture 7: Overexploitation 1 Flashcards
Lecture aims
1.Define overexploitation and compare its impacts to other drivers of biodiversity loss
2.Discuss different examples of overexploitation
3.Discuss the drivers of overexploitation
Define overexploitation and compare its impacts to other drivers of biodiversity loss
Overexploitation is the second biggest driver of biodiversity loss after habitat loss:
See figure from WWF Living Planet Report 2018
See Caro et al 2022 conservation letters
^ Some people are concerned that excessive focus on climate change in
research and media distracts from the principal threats to biodiversity.
^ One might argue that this is misleading because the threats of land-use change and overexploitation are split over multiple categories each
When in fact
Land-use change (i.e. agriculture & aquaculture) and overexploitation (i.e. resource use) in 2022 were still the biggest threat to biodiversity
The IUCN red list
The IUCN Red List is the authority on species’ risk of extinction
Determination of threats is an essential aspect of red-listing
For each species they conduct an assessment that considers current status and main threats
The Red List categorises threats according to a hierarchy,
including a category for Biological Resource Use
If we take the Critically Endangered Sunda Pangolin as an example – hunting & trapping is clearly the major threat. We can also see the driver of this exploitation is food and medicine (under uses)
Another example is the Endangered mahogany tree
Again, resource use is a major threat. This time through logging for timber with a huge variety of uses such as household goods
Biological resource use = exploitation = using nature to provide goods
*Exploitation is a loaded, negative word, but we basically just mean utilising a provisioning ecosystem service – be that wood and fibre, or wild plants and game
biological resource use exploitation is not inherently ‘bad’
it is bad to use them unsustainably and overexploit them
*Ecosystem services are one of the ways in which we can put a value on nature, so it doesn’t make sense to stigmatise the use of nature
Overexploitation = harvesting a natural resource at an unsustainable rate
*This is simple economics
*As you increase harvesting effort, you will increase harvested yield
*But, there comes a point at which the increase in yield starts to diminish for the same increase in harvesting effort – this is the zone of diminishing returns
*This is a strong sign that we are harvesting at a rate faster than the resource can be renewed
Once we get beyond the max yield, increasing effort actually gives decreasing return
see generic overexploitation curve in notes
&
similarity of a classic example of overfishing from OurWorldinData
^ We often don’t know the wild fish population, but we do have a good idea of fish catch per unit of fishing pressure, and this can tell us how sustainable the fishing pressure is
*As we increase fishing pressure/effort, fish catch increases but only up to a point – the Maximum Sustainable Yield
*Beyond this point, catch starts to decrease for increased effort, indicating that stocks are becoming depleted
We know that land-use change is the biggest driver of biodiversity loss, whether through habitat conversion to agriculture or habitat degradation
BUT, overexploitation could be happening in any of these land-use types
Types of overexploitation:
Overgrazing in pasture – livestock graze more grass than can be replenished
e.g. Lake District condition for example is ‘sheep wrecked’
Under the EU Common Agricultural Policy, UK farmers were paid ‘headage’ payments for number of livestock which led to excessive stocking density that land cannot support
*The UK upland landscape is a stark example of overgrazing – at the same elevation and latitude elsewhere in Europe, tree and alpine meadows thrive
*In the UK (Scafell Pike shown here), mountainsides are barren & “sheep-wrecked” as George Monbiot puts it in his book, Feral
*Driven by perverse subsidies
*The fact that many livestock need supplementary feeding is clear evidence that pasture alone cannot support them, and cropland that could have fed humans must instead be used to feed livestock
Further evidence of overgrazing comes from the observation that species that are otherwise widespread in a similar climate and latitude are confined to steep ravines on high mountains – where they are safe from sheep - As seen in the distribution of Mountain Avens
Types of overexploitation:
Overharvesting in croplands = farmers remove more soil nutrients than can be replenished
See ‘An introduction to agroforestry’
Nair et al 2021
*In a natural ecosystem, there is a cycling of nutrients as plants take up nutrients to grow, plant matter falls and soil biota break down and re-release nutrients back into the soil
*In an intensively managed cropland, plants are removed and this takes with it the nutrients that the plants had taken up from the soil
*Nutrients typically replenished with synthetic fertiliser, but this often does not restore correct nutrient balance
*There are other ways of doing agriculture that avoid depleting nutrients and water
e.g. composting non-edible parts of crop plants and returning the mulch to the field
Types of overexploitation:
Overfishing – fishers harvest more fish than can be replenished
See 5 centuries of cod capture in eastern Canada Schjins et al. 2021
Much of the research on overexploitation and sustainable yields comes from fisheries
That is because we have seen the catastrophic impacts of overfishing
– complete fisheries collapse in North Atlantic cod, for example
Types of overexploitation:
Overharvesting timber – foresters harvest more timber than can be replenished
1990: Sabah retained ca 5000 km2 of primary lowland forest,
most within the Class II Forest Reserve
2010: less than 700 km2 remains - almost none outside of
protected areas
See Reynolds et al 2011 phil. trans. figure:
post-war industrialisation of logging over time resulting in harvest decline with increasing effort instead of stopping logging they opened new areas for harvest using helicopters to shift timber from steep slopes until decline occurred again
Forestry is another industry with a lot of research on harvest sustainability
In Malaysian state of Sabah, the main driver of land-use change and hence forest loss in Sabah over the past 20 years has been the demand for palm oil
*The increase in the extent of timber plantations over the past 20 years has been less marked
*Extraction volumes remained relatively constant at 10–12 million m3/acre through the 1970s and 1980s
*By 1999, the volume of timber extracted from natural forests had fallen to approximately 3.4 million m3/acre
*With the early release of logging coupes & the opening of previously unworkably steep slopes through the use of helicopter yarding techniques, decline was temporarily arrested and for 10 years, from 2000 to 2009, timber production averaged almost 5 million m3/acre
1960s-1990s: Harvesting volumes from Ulu Segama Forest Reserve averaged ~120 m3/ha
(compared to e.g. 15–20 m3/ha in Brazilian Amazon† or 2.66m3/ha in Chiquibul Forest, Belize‡)
Mid-1990s: Harvesting ceased, entering prescribed rotation of 60 years
Late 90s: premature second round of logging, regulations were discarded
^ made a deal with a chinese company for a plantation so they clearlogged the area
*Harvesting volumes in the YSFMA were among the highest recorded for any tropical forest globally
*Essentially a salvaging operation in advance of a near complete clear fell
*Cutting diameter limits, which had been strictly enforced at 60 cm diameter at breast height (d.b.h.) during the first cut, were reduced to 40 cm d.b.h.
*Range of harvestable species expanded to include trees other than dipterocarps
*The harvesting rate was also greatly accelerated from 2000 to 5000 ha per annum when the Ulu Segama forests were first logged in the 1970s, 1980s and early 1990s to ca 20 000 ha per annum during the re-logging operation.
The net harvestable area was also considerably expanded through the issuance of special licences that permitted helicopter yarding on the very steepest slopes (greater than 25 degrees)
Area was overharvested and the contract fell through so no plantations were established
How does primary forest compare to logged forest?
See Senior et al 2018
Recovering forest (secondary) has a very different composition to old growth primary
Interestingly no microclimatic differences were observed
*The result is a forest that is structurally & biologically different
*(Although climatically the same, at least in the understorey!)
Primary forest – less dense understorey (shaded out by canopy), multiple layers of vegetation, many large trees
Logged forest – hot mess of understorey with vines, spiky rattans, ginger, bamboo & many regenerating saplings, not many large trees
Types of overexploitation:
Overharvesting game – hunters harvest more game than can be replenished
Martha was the last passenger pigeon, she died at Cincinnati Zoo on 1 September 1914
- This species lived on acorns from oaks as well as chestnuts and American beech
^note these species do not fruit every year
*Based on written accounts, the sound of these flocks was deafening and their combined weight would often break tree branches
Passenger pigeons were often cited as the most abundant bird in the world
How did we go from the image on the right - to just Martha? Mainly hunting!
*It was assumed that a species so abundant could not possibly go extinct from hunting
*But these flocks were so big and dense, concentrated in space and time, that it was relatively easy for people – particularly European colonisers – to hunt them in massive numbers for food and feathers
*It was said that simply holding a stick in the air would yield some birds
*European colonialism was also responsible for widespread forest loss throughout their territory, and increased competition for tree masts for pigs put to pannage
*Because the species was reliant on large flocks for protection from predation and to successfully breed, they were not able to recover from low population sizes
Hung et al 2014 PNAS
Smith et al 2021 Proc. R. Soc. B.
*Several genetic studies have been done to understand the mechanisms for the observed crash
*Probably experienced frequent and dramatic population fluctuations following climatic, food-resource, and other ecological variations, thereby increasing its extinction risk
^ an ‘outbreak species’ a bit like locusts – large natural population flux
*E.g. carrying capacity tracks oak coverage – expanding from end of LGM, peaking 10ybp, stable & then declining recently
*BUT, in geologic time, this was a species whose population was otherwise expanding
*[Last Interglacial began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period]
*[Last Glacial Period (LGP), occurred from the end of the Last Interglacial to the beginning of the Holocene, c. 115,000 – c. 11,700]
Drivers of over exploitation
Overexploitation is up there as the most prevalent threat facing threatened or near-threatened species on the IUCN Red List. Largely this is through logging, and then hunting, fishing & gathering of plants:
See Maxwell et al. (2016) Nature
‘Big Killers’ figure
As for all the threats we have and will discuss, the drivers largely come down to economics: see WWF (2018) Living Planet Report
Drivers;
Consumption
Production
Markets
Finance
Governance
Pressures:
Agriculture
Forestry
Fishing and hunting
Energy and transportation
Mining
Infrastructure
Threats:
Habitat loss and degradation
Overexploitation
Climate change
Pollution
Invasive species
Biodiversity
Species
Ecosystems
Benefits from nature:
Provisioning
Regulating
Supporting
Cultural
If you get diminishing returns for increased effort, why would you continue?
One of the main reasons for this is a concept referred to as the tragedy of the commons:
See Hardin 1968:
- Use of the commons is below the carrying
capacity of the land. All users benefit.
2.If one or more users increase the use of the commons beyond its carrying capacity,
the commons becomes degraded. The cost of the degradation is incurred by all users.
3.Unless environmental costs are accounted for and addressed in land use practices, eventually the land will be unable to
support the activity.
Case study: The Tragedy of The Commons
*Imagine commons land with a carrying capacity that equates to a maximum milk production of 1000 litres/day
We have 20 farmers, each with 5 cows;
20 farmers *5 cows *10 litres milk = 1000 litres/day:
1 cow = 10 litres milk (1000 litre carrying capacity / 100 total cows)
5 cows = 50 litres milk
Each farmer gets 50 litres milk/day from their 5 cows
BUT, there is no regulation of what each farmer is doing, and the land is shared….
How much milk would 1 farmer get if they secretly added 1 cow?
If 1 farmer grazes one extra cow then:
. 1 cow = 9.9 litres milk (1000 litre carrying capacity/ 101 total cows)
. 6 cows = 59.4 litres milk
. 5 cows = 49.5 litres milk
· Benefits the individual to add a cow & cost is shared (9.9 vs. 10 litres milk per cow)
· Alternatively, per cow milk yield could be maintained now but decline in future
see Lim et al 2005 teaspoon study:
*In this classic study on disappearing teaspoons, authors observed substantial loss of teaspoons from shared tearooms
*Half-life of teaspoons was shorter for the communal tearooms
*Over 1/3 respondents admitted to stealing a teaspoon even though over half believed that stealing teaspoons is wrong
*As the teaspoons are a shared resource and their use is unregulated, this is argued as an example of Tragedy of the Commons
*One individual can steal a teaspoon to their own benefit, and the cost is shared among all users who now have 1 fewer teaspoon to share
Externality
*The Tragedy of the Commons leads to overexploitation because it facilitates negative externalities – the benefit is to the individual and the cost is shared
*The cost/benefit trade-off favours selfish behaviour
Can we internalise neg. externalities?
Example 1
Perverse farming subsides allow farmers to make a profit even when overexploitation leads to insufficient output (yield) for the costs of input (machinery, fertiliser, seed)
^ Removing these subsidies helps to internalise the externality because the farmers would then suffer the financial costs of overexploitation
^ Not necessarily ethical to do this and only this – farmers have simply been doing what they were incentivised to do
Example 2 “Polluter pays” e.g. Canada’s carbon pricing
^ Removing gov. subsidies helps to internalise the externality
Temporal discounting
More economics: If I offered you £100 now or £1000 in 10 years, what would you choose?
*Generally speaking, people place higher value on getting a resource now than in the future, even if the future yield is likely to be higher
*This can lead to overexploitation because people undervalue future yields
*Many drivers of temporal discounting – lack of trust, uncertainty of the future, selfishness, perceived lack of need in future relative to now
Do natural landscapes reduce future discounting in humans?
*Interestingly, there is some suggestion that spending time in nature can itself alleviate future discounting
^ Those who spend time in nature are more likely to be happy to wait for the payoff
Conclusive points
using natural resources is not inherently bad
There are many examples where sustainable use can support livelihoods and even benefit nature
The problem lies in effective use of economic instruments & an understanding of human decision-making
Summary
*Overexploitation is one of the biggest drivers of biodiversity loss
*Overexploitation happens when a resource is utilised at an unsustainable rate
*It can happen in pretty much any system (and not confined to natural resources either…)
*Ultimately, it is driven by market forces, governance and human behaviour
