Human Activity Flashcards
(49 cards)
Ecological succession
Ecological succession is a process of change in a community with time
Ecological succession can affect biotic and abiotic interactions in the community, which in turn can affect the species present and their population size
Succession
Communities change progressively over time, with one community being replaced by the next in the process of succession
Succession steps
- Pioneer plants colonise (lichens)
- Soil formation
- The early colonising plants have characterised that make them successful
- A new community forms
- As the succession process slowly continues, biodiversity increases
Primary succession
Is the colonisation of new sites by communities
Occurs on bare sites that have no organisms inhabiting the affected area
E.g. bare rock or areas with no soil
E.g. new sites are formed when volcanic eruptions form new rock or lacier retreat to expose bare rock
- Starts with the arrival of living things such as lichens that do not need soil to survive (Called pioneer species)
- Acid produced by the lichens attack and weather the rock surface.
- This creates the attract of soil to form in rock cracks. Mosses start to establish themselves
- As lichens and mosses die, it thickens the soil and adds nutrients
- Bacteria, fungi and simple invertebrate animals move in. A simple community now exists
- as ore soil and nutrients are added to the environment, more complex organisms form grasses to ferns to shrubs start to establish themselves
- taller plants add shade and root systems increase weathering processes
- me animals immigrate into the community from insects to smaller herbivores then carnivores
Secondary succession
Begin in a place that already has soil and was once the home of living organisms
Takes place on existing soil
Occurs after catastrophic events (like fire, cyclones or tsunamis) wipe out all life on the clearing land (a farmer clearing a field or deforestation)
With the soil still present and possibly also some root systems and seeds still in the soil, the community comes back faster
Grasses and annual plants appear first, followed by some shrubs and bushes and then trees
Animals gradually immigrate form the invertebrates to insects to herbivores to carnivores
Climax community
Are a stable group of plants and animals that is the end result of the succession process
Little or no succession takes pace in the community
Slow-growing, long-lived species (K-selected species)
Does not always mean big trees
- grasses in prairies
- cacti in deserts
Unstable community
Going through succession, especially after unpredictable events. Population explosions of colonisers often occur
Exploited by r-selected species
Stable communities
Exist close to carrying capacity at relative equilibrium. Can be a climax community
Many K-selected species exist within
Fire - a dynamic factor
All ecosystem change over time
Fire is neither innately good or bad, it is just an agent of change
Roles of fire in ecosystems
Reduces probability of catastrophic fire
Nutrient input into soil
Control of insect pests and disease
Maintains species diversity
Reduces probability of catastrophic fire
- Fire intensity depends on fuel load and weather
- In many forest types the fire regime ( the historical frequency and intensity of fire natural fires) reduces fuels
- Means that future fires low to moderate intensity instead of catastrophic
Nutrient input into soils
- soil nutrients are usually tied up in organic matter. These are released after fire, increasing availability to plants and soil microorganisms
- fewer leaves left to catch rain and plants using water will allow moisture to reach the soil
- blackened soil and greater exposure to sunlight, wind and evaporation, however, will work in the other way to dry the soil
- the fire may have created an impermeable crust at the soil surface, if organisms matter on the ground was heated by he fire into a waxy residue. May lead to increased soil erosion through surface runoff-off
- ash and charcoal provided added nutrients back to soil
Control of insects pests and disease
Some insects populations are apparently controlled by fire
High temperatures and make smoke directly kill adults, larvae and eggs
Reduced tree density decreases susceptibility to infect attach and disease (density-dependent factors)
Some insect pests can also invade after fire, feeding off the dead materials
Maintains species diversity
Effect on vegetation i classified according to their response to fire
Fire-intolerant plants - highly flammable and completely destroyed
Fire-tolerant plants - able o withstand some forms of fire and grow despite some damage
Fire resistant plants - suffer little damage
Maintains species diversity
Many different effects on fire on plants
- negative - individual death
- positive - altered surface light/ conditions releases canopy seeds or stimulates germination of seeds
- increased - situated seed dispersal distanced, flowering, productivity and seed establishment
Some plants have back up protection from fire, so that they are capable of regeneration afterwards
Epicormic buds - dormant buds tat only grow after leafy tissue is destroyed
Lignotubers - woody tuber at the roots (safe form the fire damage) that stores water and food to support regrowth
Most animal species respond predictable to the passage of fire, although the responses vary among species. Some flee, seek refuge, or rescue young. Other species are attracted to burning areas (forage during fires or red on charcoal and ash after fires)
Maintains species diversity
Vertebrates
- mortality - related to size of fire and rate of speed
- loss of nesting sites and young but…
- cavity nesters and insect foragers love dead trees
- immediate increases in food sources for predators
Maintains species diversity
Invertebrates
- mortality - high in burn area for life stages in litter or on plants
- rapid invasion by some species may follow burn
- after a fire, the species composition changes to early successional animals
- birds - some prefer more open conditions, periodic fires recreate scrub habitats
- large mammals - some benefits from flush or new growth
- small mammals - increased seed production important for food
Human impact on resources
- human impact on the natural world has increases dramatically as the scope and intensity of human activity have increased
- unresolved problems include the loss tropical forests, the build up of greenhouse gases and the loss of biodiversity
- the impact of humans on the global environment is the result of resource use, rapid population growth, large population size and disproportionate distribution of resources
Global issues
- threats to biodiversity from all sources are quickly reaching a critical level. Current extinction rates are 100 to 1000 times higher than pre-human levels
- aquatic environments such as coral reefs and freshwater habitats in lakes, rivers and wetlands are all at risk of degradation (deterioration of the ecosystem through the depletion of its natural resources)
Habitat destruction
Human impact on ecosystems
- deforestation worldwide is a huge issue
- salinity - removal of natural vegetation which causes the underground water table to rise
This pushes the salt to the surface. Greatly reduces biodiversity and can make the all completely uninhabitable - fragmentation - when once continuous habitats become separated form one anther
Small habitats can only suppress small population making organisms more vulnerable to extinction
Introduced species
Human impact on ecosystems
- species can be introduced unknowingly (in the post, on shoes or other organisms) or deliberately
- they pose a major threat to ecosystems, as they often have no natural predators and compete with native species for resources
- goats, pigs, wheat, other cereal crop, foxes, black rats, camels, cats and dogs are all introduced species to Australia. Some have become pests, out competing the native organisms
- often species are deliberately introduced as a biological control agent
- however, some bio-control agents may even become pests themselves. The cane toad was introduced to Austria o control grey cane beetles and is now a major threat to native wildlife
Agriculture
Human impact on cecosystems
- nature maintains biodiversity through the natural process of succession. Agriculture greatly alters this
- monoculture - where one species of organism is grown (e.g. a wheat of organisms is grown (e.g. a wheat field)). Monoculture requires large amount of fertilisers and pesticides
- intensive (industrialised) agriculture uses large amount of fossil fuels fuel energy, water, fertilisers and pesticides to increase he net production (crop yield)
European settlement and urbanisation
Human impact on ecosystems
- the first inhabitants of Australia - aboriginal and Torres Strait Islanders have lived off most of the land from at least 40,000 years ago
- they altered the natural environment of Australia through fire regimes, which increased the prevalence of fire tolerant species
- hunting by the first Australians also saw the extinction of megafauna (elephant sized wombats and 6m long goanna)
- with the arrival of Europeans to Australia the greatest change in natural environments occurred
- extensive land clearing from farming, irrigation & damming water supplied and urbanisation began
- even as early as in the 1850s, it was noted that plant species were disappearing, erosion was evident and print water supplies were vanishing in Australia
- urbanisation - is a pollution shift from rural to urban areas or the gradual increase in the proportion of people living in urban areas
- urban ecosystems use a large amount of natural resources, most of high are not found there and have to be brought into the urban environment. They also produce a large amount of water (rubbish, air and water pollution)
Water flow and Eutrophication
Human impact on ecosystems
Human requirements for water have resulted in:
- irrigation - channels water to where it is needed, meaning it alters the natural flow and removes vegetation
- construction dams and reservoirs to store water for our use. Can result in downstream ecosystems being starved for water and shut off
- degradation of urban waterways and streams by pollution and stormwater drains
- Eutrophication is a term describing the enrichment of waters with nutrients. It often results in excessive growth of weed and algae
- miscroorganism decompose the organism matter in the polluted water and their activity increases the uptake of dissolved oxygen
- this reduces the amount of dissolved oxygen available to their aquatic organism and may subsequently cause their death
