Lecture 5: Habitat Fragmentation & Degradation Flashcards
Habitat fragmentation vs habitat degradation
Habitat degradation: a reduction in quality of habitat.
Includes pollution & activities leading to desertification, erosion, & sedimentation.
Habitat fragmentation: larger continuous habitat becomes divided into smaller patches.
Reduces habitat area + changes the structure of the remaining habitat.
Habitat degradation: Pollution
- Most widespread.
- Largest environmental cause of human disease & premature death.
- Causes ~ 9 million deaths pa (per year) (16% of deaths worldwide).
Habitat degradation: Pollution
Pesticides
- Green revolution (use of pesticides/herbicides to boost production but caused detrimental environmental effects).
- They brought to world’s attention in 1962 by Rachel Carson’s book ‘Silent Spring’.
- Focused on pesticides like DDT - bioaccumlation.
- E.g. if washes into water might find low concentrations, but in the trophic pyramid everything above needs to eat more of what’s below so producers become more concentrated then things that eat those become more concentrated and then more and more concentrated till you get to the top of the food chain. E.g. water = 0.0000003 ppm (parts per mill), producer (e.g. zooplankton) = 0.04 ppm, predator (e.g. fish-eating birds of prey) = 25 ppm.
- This happens when have chemicals that are stored in body.
- Caused problems particularly for predators (birds of prey) in their reproduction & populations crashed.
- Now banned across most of world.
- Still lots of agrochemicals in use that kill non-target species & remove natural predators (directly or indirectly) & further increasing reliance on agrochemicals.
Habitat degradation: Pollution
Pesticides continued
- Agrochemicals undergo stringent (strict) tests to investigate their toxicity to a standard suite of organisms (e.g. plankton to dogs). Tests for how many it kills but doesn’t look for sublethal effects (or effects on other organisms not part of that standard suite).
- E.g. Neonicotinoids are widely used insecticides. Have sublethal effects on bee behaviour by impairing foraging behaviour, homing success, navigation performance & social communication. Now banned in UK and EU but farmers can be granted exemptions.
Habitat degradation: Pollution
Oil spills
- Directly kills many species e.g. in sea birds feathers means they not waterproof so can’t survive.
- Clear-up processes e.g. chemical dispersants can cause further damage.
Toxic metals
- Result from manufacture (e.g. leaded fuel, batterys) & directly kill many species.
- Can bioaccumulate.
Eutrophication
- When fertilisers (nitrates & phosphates) get into aquatic systems e.g. through run-off from agricultural land & dumping waste.
- Causes algal blooms which shade bottom dwelling plants and decomposition (when they die) uses up O2. Causes a dead zone where lots of fish die due to lack of O2.
- Can be difficult for ecosystems to recover even if pollution removed.
Habitat degradation: Pollution
Acid rain
- nitrogen & sulphur (from burning fossil fuels etc) released into air (& combine with H2O) form nitric and sulphuric acids, which lower the pH of rainwater (more acidic).
- Can kill plants & animals.
- Acid rain clouds can travel 100’s of miles, effecting ‘pristine’ ecosystems.
- Reducing in Europe & North America.
- Increasing in East & South Asia (as lots of manufacturing has moved here from Europe & North America).
Pharmaceuticals
- E.g. medicines, cosmetics, disinfectants, detergents (that we throwing down sink).
- Emerging pollutant source - little is known about consequences.
- Antimicrobial resistance can be caused by antibiotic misuse (e.g. antibiotic resistant TB, in UK most is treatable from course of antibiotics but in other parts of world it is resistant).
- Hormones e.g. from contraceptive pills (even from urination) can impact aquatic animal reproduction (e.g. in fish species can shrink gonads (reproductive organs) & reduce reproductive output).
Habitat degradation: Pollution
Plastics
- Fast growing form of environmental pollution.
- Problematic in marine ecosystems - get washed in from land.
- More than 5 trillion pieces of plastic weighing <250,000 tons are afloat in world’s oceans.
- Can be mistaken for food or break down releasing toxins and microplastics.
Light, sound and smell pollution
- Affect behaviour.
- Light pollution impacts circadian rhythms & distrusts normal feeding and breeding behaviour.
- E.g. street lighting leads to 47% decline in moth caterpillar abundance in hedger grows and 33% decline in grass margins. Distrusts feeding behaviour & egg laying behaviour.
- Sound pollution impacts vocal communication (e.g. birds singing next to a busy road so need to move away from areas with roads), orientation and foraging.
- E.g. blue whale foraging is distrusted by boat traffic.
- Smell pollution.
- Little investigated.
- Disrupt natural scent communication (reproduction, social behaviour).
Habitat degradation: Desertification
- Poor soil & water management leads to further drying of already dry areas.
- The Sahara was grassland (become desert not related to humans tho).
- Is natural process but rates of desertification are increasing.
- E.g. Large wetland areas are drying up. Wetland habitats are stop overs for migrating species so if lost those species that migrate loose those vital stop offs.
- E.g. The Mesopotamian Marshes, Iraq. Large marshland drained by Saddam Hussein but now in process of restoration.
- Most cases aren’t on purpose e.g. Aral Sea. Worlds 4th largest inland lake, irrigation for cotton production (requires lots of water) drained it in 30 years. Led to ecosystem collapse and human tragedy (relied on for income/food). Restoration has started.
Habitat degradation: Erosion & sedimentation
- Erosion a natural process but current rates of soil erosion are 11-38 times faster than previous levels.
- Due to deforestation (removes the roots that hold soil in place), overgrazing, & unsustainable agricultural methods (leave soil exposed).
- Causes degradation of agricultural land (soil degrades, couple cm’s of soil a year disappears).
- Deposition of soil (sedimentation, soil that gets washed away gets deposited else where) chokes up natural landscapes and leads to eutrophication.
Habitat degradation: Solutions
- In environmental regulation at local, national and international levels. (Lecture 10)
- Organisations that campaign through protesting.
Habitat Fragmentation
- Divides larger habitats into smaller pieces.
- Associated with habitat loss (tends to be that habitats get fragmented then lost).
Habitat Fragmentation: Biological consequences
- Variation in patch: size, shape, number, isolation.
- Leads to variation in species responses.
- Mostly negative but can be beneficial for some species.
- Aspects of habitat fragmentation don’t correlate linearly with habitat loss, as habitat is lost: a) patch size tends to decrease (linearly), b) isolation will increase in non-linear way, c) number of patches increase first, but then decreases as more lost, d) amount of edge habitat increases then decreases.
Habitat Fragmentation: Biological consequences
Consequences of reduction in patch size:
- Impact number of species they can support. Species-area relationship.
- As more habitat lost less and less species can be supported.
- Species have extinction thresholds: minimum habitat size that are required for them to persist. Different for different species.
- Allee effects: small populations are disproportionately likely to go extinct. (Growth rate is highest at intermediate density/populations, usually small populations would have a relatively high growth rate, but Allee affects reduces the growth rate of the population when its small, maybe can’t find mates, dilution effects from predators etc).
- Behavioural aspects can have big effect, e.g. tiger needs a lot of space & prey to survive, so extinction threshold in terms of the area needed is gonna be low.
- Might get allee affects in social species e.g. meerkats, need a minimum group size to thrive.
Habitat Fragmentation: Biological consequences
Edge effects
- Smaller patches have proportionally more edge (as gets smaller more is close to the edge), so do more elongated patches.
- E.g. Haddad et al (2015) found that 70% of worlds remaining forest is within 1 km of a forest edge & nearly 20% is within 100 metres of an edge.
- Fragmentation will negatively affect species that don’t like to live near edges.
- Edge habitats often less resistant (from wind, drought, fire etc but more likely to get more light & nitrogen).
- Edge habitats vulnerable to invasive species.
- The behaviour of the species determines which will thrive or decline.
- Dominated by generalists that adapt well to anthropogenic landscapes.
- Predation often high.
Habitat Fragmentation: Biological consequences
Human-wildlife conflict - anthropogenic food sources and edges near humans more opportunity for conflict.
Mitigate the risk:
- In Asian elephants, human mortality occurs more when chasing wild elephants using firecrackers.
- Lone male elephants more likely to attack people.
- Behavioural solutions - e.g. using beehive fences to deter elephants (they don’t like bees).
