Tropical ecosystems Flashcards
(23 cards)
Ecosystem
Interrelationship between plants and animals and their biotic and abiotic environment
Community
A group of populations living and interacting with each other in a common habitat
Population
Just one species
Net Primary Productivity
How much organic material is produced per year in an ecosystem
- Water availability
- Heat
- Nutrient availability
- Age + health of plants
Biomass
Measure of energy stored in an ecosystem
Biodiversity
The variety of habitats, species and genetic diversity in an ecosystem
Succession
The spatial and temporal changes in a plant community over time moving towards a climax (a stable, mature ecosystem).
Succession processes
Pioneer stage:
- Few nutrients, low organic matter
- Small, hardy species
- Low biodiversity
Late succession:
- More organic matter
- Higher biodiversity
- Larger, longer-living organisms
- Nutrients often held within biomass (e.g. trees)
Climate is the key factor controlling biomes (e.g. rainforest, temperate woodland).
Soil (edaphic control) can affect vegetation within a climate region
Sub-climax and paglioclimax
A sub-climax is a temporary stage in succession where a climax community is prevented by natural factors (e.g. flood, hurricane, tsunami), but may return if conditions stabilise.
A plagioclimax is a permanent vegetation state caused by human activity (e.g. burning, grazing).
eg. maintained grasslands through burning
Succession in Montserrat
Chances Peak once had rich tropical rainforest.
Volcanic activity from the 1990s led to:
- Acid rain, gases, heat, and ash
- Vegetation loss, especially cloud forest
- Lahars destroyed Tar River valley forests
- pH of lakes dropped to 1.5–2.0
Recovery process:
- Begins with pioneer species like Cecropia (bird/bat-dispersed, light-tolerant)
- Followed by shade-tolerant plants as canopy develops
- Seed sources from nearby forests (e.g. Centre Hills) support regeneration
- Full recovery may take decades (e.g. 40 years in Puerto Rico)
Vegetation in tropical rainforests
Types of forest:
- Heath forest over sand
- Brackish water forest
- Peat swamp forest
- Fresh water swamp forest
- Mangrove forest
- Tropical lowland evergreen rainforest
- Tropical lower montane rainforest
- Tropical upper montane rainforest
Layers of a rainforest
Layers:
- Emergent – (45–50m)
- Canopy – (25-30m)
- Under Canopy – (5-20m)
- Forest floor – (0-5m)
Vegetation adaptations
Adaptations:
- Butress roots
- Shallow roots
- Tall, thin trunks to reach light
- Toxic leaves/ seeds
- Drip-tip leaves
- Lianas (climbing vines)
- eg. Swiss cheese plant
- Epiphytes grow on trees
- Pitcher plants trap insects/small mammals
- Saprophytes (fungus) break down dead matter, recycle nutrients
Animals in tropical rainforests
- Many animals are highly specialised
- Feed on specific fruits, leaves, or insects
- Pollination by insects, birds, bats (not wind)
- Support complex and stable food webs despite low animal biomass
Features of rainforests
Constant heat and humidity → stable environment
Species become highly specialised
Organisms rely on specific food sources
Human disturbance often causes irreversible damage
Net Primary Productivity (NPP) = 2200 g/m²/year
Two types of nutrient cycles
Gaseous cycles (e.g. nitrogen): more complete
Sedimentary cycles (from rocks): more vulnerable to disruption
Nutrient types
Macronutrients (needed in large amounts):
- Oxygen, Carbon, Hydrogen, Nitrogen
Micronutrients (trace elements):
- Magnesium, Sulfur, Phosphorus (needed in small amounts)
Nutrients cycle through ecosystems
Plants absorb nutrients (from air/soil)
Animals consume plants, taking in nutrients
Nutrients return to soil through decomposition
Nutrient cycles interact with soil, air, and food chains
Factors influencing nutrient stores and transfers
- Rainfall and decomposition rates
- Vegetation type and density
- Fire and overland runoff
- Soil erosion and eluviation
- Plant age and health
- Weathering
- Growing season length
What is nutrient cycling like in tropical rainforests?
- High input from weathering and rainfall
- Most nutrients held in biomass (due to year-round growth)
- Small soil store (nutrients quickly absorbed or leached)
- Fast decomposition due to heat and moisture
- Deforestation causes rapid nutrient loss through leaching and runoff
What is nutrient cycling like in savanna ecosystems?
- Shorter growing season than rainforest
- Fires reduce litter store
- Lower biomass store
- Soil store is relatively large
- Seasonal drought and fire are key limiting factors
Gersmehl’s nutrient cycle
Indicates the
stores and transfers of nutrients:
- Biomass
- Litter
- Soil
Rwanda civil war and rainforest
- Political and economic breakdown in the DRC has starved the Virunga park of funds
- In the 1960s, much of the big game was killed during the civil war in the
Congo.
Tourism in the park is limited, thereby reducing the park’s
revenue - Villagers in the park have depleted the forest and overfished
the lake. - The Rwandan civil war (1990–94) intensified pressures on the land.
- Park was looted by Rwandan refugees and soldiers
- 300km2 of forest destroyed in 6 months
- 900,000 refugees lived in Virunga
