GEOG20009 Lecture Notes - Lecture 11: Keystone Species, Seagrass, Ecosystem Services

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LECTURE 11: COMMUNITIES, BIOMES, ECOSYSTEMS cont.
FOOD WEBS
Food webs and keystone species: keystone species are a plant or animal that play a unique crucial role in ecosystem
functions
o Without them, food webs and ecosystems would be dramatically different or cease to exist all together
o E.g. Sea otters and urchins sea otter numbers dropped, who ate sea urchins sea urchins destroyed
sea grass habitats and desertified it eradicated everything else
Simple and complex food webs
o Removing species is highly risky
o Removing a single plant from a food web has little impact on a
predator which relies upon a range of food sources
o In simple food webs, removing a single plant species may severely affect the predator more
vulnerable to change
o Removing a predator from a food wed creates a ‘shock wave’ that cascades down trophic levels
Productivity of system regulates resource availability resource availability regulates the system
PRODUCTIVITY
Latitudinal variation in temperature as important controlling variable on productivity
Temporal pattern: primary productivity varies with time (seasons, interannual)
Temperature and elevation influence productivity
Global atmospheric circulation air travels in cells, falls and rises
Regionally distinct zones of vegetation across Earth main drivers are temperature
and moisture gradient
Ecosystem productivity: open ocean and tropical rainforest very high, other marine
ecosystems not as high, savanna, boreal forest and other forests all high
Biomes
Biome: a biotic community, a distinct biological community
Has formed in response to a shared physical climate temp and precip
Common characteristics for the environment
Similar characteristics can arise in distant biomes through convergent evolution
Ecoregions
Ecosystem: community of living organisms in conjunction with the abiotic components of their environment
interacting as a system or functional unity
Many different classification systems
Largest = biosphere, also includes smaller scale systems
Boundaries transition in environmental conditions (ecotone) has unique adaptations and communities
Components: water, nutrients, topography, weather, disturbances, species, populations and communities
Marine Ecoregions
Marine communities are divided into 2 major vertical zones, based on
penetration of sunlight
Also based on depth and configuration of the ocean bottom at which they are
found
Spatial patterns: seen across the globe as belts, meaning influence of sunlight is a
key factor
Annual NPP: highest along coastlines, then follows major ocean currents
Global scale productivity driven by water, temperature and nutrient availability
Ecosystem Services
Provisioning services: production of
food and water, raw materials, energy
Supporting services: nutrient cycles,
primary production, soil formation
Regulating services: climate control,
carbon sequestration, disease control
Cultural services: spiritual, recreational
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Document Summary

Food webs and keystone species: keystone species are a plant or animal that play a unique crucial role in ecosystem functions: without them, food webs and ecosystems would be dramatically different or cease to exist all together, e. g. Sea otters and urchins sea otter numbers dropped, who ate sea urchins sea urchins destroyed sea grass habitats and desertified it eradicated everything else. Simple and complex food webs: removing species is highly risky, removing a single plant from a food web has little impact on a predator which relies upon a range of food sources. In simple food webs, removing a single plant species may severely affect the predator more vulnerable to change: removing a predator fro(cid:373) a food (cid:449)ed creates a (cid:858)shock (cid:449)a(cid:448)e(cid:859) that cascades do(cid:449)(cid:374) trophic le(cid:448)els. Productivity of system regulates resource availability resource availability regulates the system.

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