6 - Tropical rainforests

• Ecosystem


  Made up of plants, animals and their surrounding physical environment, including soil, rainwater and sunlight
• Ecosystem


  • Important interrelationships link together the biotic (living) and abiotic (non-living) parts
  • Physical linkages between different parts (animals eat plants)
  • Chemical linkages (mild acids in rainwater speed up decay)
• Ecosystems can be any size: local, regional, global biomes, or the entire Earth
• Biotic community of an ecosystem

  • Plants or primary producers
  • Herbivores or primary consumers
  • Carnivores or secondary consumers
  • Top carnivores
• Food chain


  Interrelationships between feeding groups, with biomass decreasing at each level
• Decomposers break down dead organic matter and animal excretions, returning nutrients to the soil
• Nutrient cycle


  Nutrients constantly recycled in every ecosystem, with pathways including input, uptake by plants, release as litter decomposes, loss in runoff and leaching
• Epping Forest is home to a large number of native tree species, a diverse lower shrub layer, and many insect, mammal and bird species

  
• Epping Forest ecosystem


  • Deciduous trees adapted to seasonal climate, with leaves shed in autumn and decomposed by spring
  • Interdependence of plants, animals and soil through nutrient cycling
  • People and ecosystem components are interdependent (e.g. coppicing, berry picking)

  
• Extreme weather or climate change can disturb ecosystem balance, but ecosystems can also show resilience and recover
• Removing top carnivores like wolves can lead to imbalances, but reintroducing them can help restore ecosystem balance
• Organisms in oak tree food web

  • Hawks
  • Owls
  • Sparrows
  • Woodpeckers
  • Blue tits
  • Spiders
  • Flies
  • Beetles
  • Aphids and capsids
  • Moth caterpillars
  • Common oak
• Figure 5.9 A food web supported by an oak tree
• Ecosystem balance


  The balance of an ecosystem that can be disturbed and needs to be restored through management
• Many species have been hunted to extinction, without a full understanding of how this could affect ecosystem balance
• In Europe and the USA, killing wolves and bears removed danger to people and their cattle
• Fewer carnivores meant that rabbit and deer populations quickly multiplied and began to eat all available vegetation, stripping the land bare, leading to soil erosion
• The ecosystem lacks balance
• Rewilding or ecosystem restoration


  The best way to restore ecosystem balance
• Grey wolves were reintroduced into Yellowstone National Park in the USA in 1995, which has resulted in numerous impacts
• The wolves have restored balance to the ecosystem and landscape
• Ecosystems are sometimes damaged in permanent ways, especially when human forces are involved, for instance by deforestation
• The removal of the forest exposes the soil beneath to rainfall, and so it can be washed away, making it impossible for the ecosystem to recover
• This is especially true in tropical rainforest regions, where heavy rain falls most days
• In the longer term, human-induced climate change could threaten the ecosystem balance of many places
• Changes in temperature and precipitation patterns for southern England might make it harder for ecosystems like Epping Forest to survive in their current form
• In some places, grass (rather than trees) may dominate in the future, if climate change predictions are correct
• Suppose that the population of beetles is reduced by disease
• This would directly impact on the numbers of woodpeckers


  With fewer beetles to eat, their numbers may decline
• With fewer beetles feeding on oak trees

  We may expect to see more oak tree growth
• Owl and hawk numbers may also fall

  Because they eat woodpeckers
• Woodpeckers are carnivorous and have multiple food sources


  They may just eat more caterpillars instead
• Figure 5.11 A grey wolf
• Reintroduction of the grey wolf. There are 16 packs of around 10 animals. Each pack kills one elk per day
• Competition from the wolves results in a decrease in coyote populations


  Male coyotes are smaller
• Reduction in grazing pressure on vegetation


  Aspen and cottonwood start to regenerate. There is more tree cover

  
• Increase in riverside trees stabilises river banks

  There is less erosion. More woody debris in rivers creates pools and provides trout habitat
• Regeneration of aspen trees attracts beavers

  Beavers begin to recolonise Yellowstone
• Beavers create ponds and flooded areas


  Which promote the growth of aspen trees
• Figure 5.10 Yellowstone National Park