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