Download An Introduction to Zonation

An Introduction to Zonation
What is Zonation?
• The patterning of ecosystems in parallel
bands .
• Occurs as a result of tides (intertidal
zones), altitude (changing biomes as you
go up a mountain), latitude (biomes),
changing soil moisture (around the edge of
a pond).
• Caused by varying environmental
conditions.
Classic Case:
Rocky Intertidal Ecology
• Rocky - hard substrate (rock)
• Intertidal - area between high tide and low tide
marks
• Ecology - the study of the interactions that
determine the distribution and abundance of
organisms.
* Interactions can be between organisms or
between organisms and their environment
Intertidal zone
• This area is is exposed to the air usually twice a
day as the tides ebb and flood
• Tides create a partly aquatic and partly aerial
environment
• Locally the tidal range is about 3 meters
• Rocky, sand, estuaries, mangroves, coral reefs,
etc.
• Patterns are similar worldwide
Tidal Zones on a Rocky Ocean Shore
Splash Fringe Level
High Tide Level
Mid Tide Level
Low Tide Level
Low Fringe Level
Spray or Splash Zone
Mostly
shelled
orgs
High Tide Zone
Middle Tide Zone
Low Tide Zone
Many
soft
bodied
orgs and
algae
Vertical zonation
• Banding pattern on the rocky shore as a result of
the rise and fall of the tides
• The distribution of organisms is in horizontal
bands
• Upper, middle and low zones
• Caused by differing tolerances of organisms to
stresses, both biotic and abiotic
Limits of organisms
• Upper limits are set by abiotic factors.
• Lower limits are set by biotic factors.
Abiotic factors
1. Desiccation
• = water loss; drying out
• Occurs at low tide due to air exposure
• Can increase with wind
• Some species are more tolerant to being in the
air (e.g. limpets, Fucus, Porphyra) and can live
higher in the intertidal zone
• Adaptations:
- close up e.g. barnacles, mussels
- lose water then rehydrate e.g. Fucus
2. Temperature
• Water temperature varies only slightly over the
year (7-12°C)
• Air temperature, however, can vary drastically
(0-30°C)
• Organisms out of the water are subject to
greater variations in temperature
– Adaptations:
– Evaporative cooling by mussels
– Eurythermal enzymes
3. Salinity
• Salinity can increase with evaporation or decrease with
fresh water input (e.g. rain)
• Euryhaline - tolerant to wide variations in salinity e.g.
mussels, barnacles
• Stenohaline - can only tolerate a narrow range of
salinities e.g. sea stars
• Adaptations:
• Close up e.g. barnacles, mussels
• Ion pumps e.g. crabs
4. Food & oxygen availability
• Many marine organisms get their food from the
water (as plankton!) they can only feed when
underwater
• Also, many marine organisms obtain oxygen
from the water
• Organisms living high in the intertidal zone have
a limited time in which they can feed and acquire
oxygen
• Adaptations:
- scaleless fish e.g. clingfish
- feed whole time they are underwater
5. UV light
• Marine organisms can get sunburns too
• Especially when out of the water
– Adaptations:
– Sun screen - natural compounds that absorb
UV
– Protective shell
Biotic factors
1. Competition
• = use or defense of a resource that reduces its
availability to other individuals (food, space, cover,
water, sunlight, etc.)
• Interspecific – Competition for resources between
species.
• Intraspecific – Competition between individuals of the
same species.
HOW?
• Interference – Direct. Aggressive behavior that
prevents other individuals from foraging, reproduction,
etc.
• Exploitative – Indirect. Use of a common resource.
• Apparent – Indirect. 2 species have the same
predator. An increase in species A increases the
prevalence of the predator decreasing species B.
2. Predation
• Animals eating other animals
• Predators can be generalists (eat a wide range of food)
or specialists (eat a single prey type)
• Refuges from predation:
• Size e.g. some mussels are too big to be eaten by
Pisaster
• Space e.g. limpets living on vertical surfaces to avoid
predation by birds
• Height in the intertidal e.g. Pisaster / mussel
interactions (Paine experiments)
3. Herbivory
• Animals eating plants
• Similar to predation interactions
• Refuges from herbivory:
• Chemical defenses e.g. sulphuric acid in Desmarestia,
bromine in Prionitis
• Physical defenses e.g. calcium carbonate in coralline
algae
• Height in the intertidal e.g. Ulva and Porphyra live very
high to avoid being eaten
Review:
In the Intertidal Zone...
• Upper limits are set by abiotic factors such
as desiccation, temperature, salinity, food
and oxygen availability, light
• Lower limits are set by biotic factors such
as competition, predation, herbivory