Download An overview on ecosystems: Ecosystems Terrestrial vs aquatic

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An overview on ecosystems:
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What are they?
What are their important characteristics?
How are they organized?
Ecosystems: units with boundaries that can be isolated for study [as any system]
1. Hierarchical: complex, adaptive, emergent
Fig. 3-4 (D&R) or Fig. 3.9 (KR8B)
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Ecosystems
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Terrestrial vs aquatic ecosystems
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The predominant biomass in forests is in trees (the bottom of the food web)
Yet the predominant biomass in aquatic systems is in fish/mammals (oceans) at the top of
the food chain
Something significantly different is going on in these different systems!
Furthermore, in between these two extremes are grassland/savannah systems where the
predominant constituent of biomass are the herbivores (grazers like buffalo, antelope, etc.),
the “middle” of the foodweb
How do we understand these differences?
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In spite of boundaries . . . and differences
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All ecosystems remain interconnected and interdependent
• Terrestrial biomes are connected by rivers
• Sediments/nutrients from land wash into aquatic ecosystems
• All share a common hydrologic cycle and a common atmosphere
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If everything is connected to everything else, . . .
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All species on Earth (along with their environments) could be considered one vast
ecosystem (landscape): the biosphere
But inherently impractical as a unit of study
How many ecosystems can be degraded or destroyed before we see effects on the entire
biosphere?
To what extent can basic global elements be altered (e.g. the atmosphere and its
temperature, the ocean and its chemical composition) before all ecosystems are affected?
What are the implications for the long-term persistence of humans?
The characteristic structure of ecosystems I
1.The environment (abiotic factors)
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Tolerance range of an individual
Tolerance ranges of the population - niche
Adaptation of populations/acclimation of individuals
Natural Disturbance
• Unpredictable (earthquake, volcano, tsunami, human activity)
• Somewhat predictable (fire, flood, changes in vegetative cover, soil chemistry)
• Anthropogenic Disturbance
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The characteristic structure of ecosystems II
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1. Abiotic Factors
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The degree to which abiotic factors are present or absent/high or low affects the ability of
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organisms to survive.
Since each individual in a population/species may have a slightly different (genetically
determined) response to a particular factor, populations will differ in their responses to the
abiotic environment, reflecting the sum of individual variation
The nature of a particular ecosystem will be a result of this underlying variation in both
abiotic factors and populations’ responses
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For every environmental factor and every population . . .
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If we drew a graph for every variable (abiotic or biotic) affecting a
species, we would have a picture of a species’ niche
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Fundamental vs. realized niches
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However just having a wide tolerance range (a wide fundamental niche) does not
‘guarantee’ a species will occupy the whole of the niche
Liebig’s law of the minimum
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For any particular population, numbers (or density) will be highest where all relevant
environmental conditions are optimal.
Some organisms have generally wide ranges of tolerance (generalists). Other have
narrower ranges (specialists).
Those with wide tolerance ranges (generalists who have broad niches) can live in a variety
of habitats. Those with narrower ranges (specialists with narrow niches) have more
restricted distributions.
Restricting any one of the many different environmental factors that influence an organism will limit the
population
e.g. plants need water, light, nutrients and proper temperatures for growth
Even if water, nutrients and light are optimum, the plants cannot survive and prosper if temperatures are
above or below their limit of tolerance
Ecologists expend considerable effort trying to quantify species niches and the population’s most likely
limiting factor(s)
Draper or Draper/Reed
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Designating large areas as biomes is somewhat of an oversimplification given the 3
dimensional structure of landscapes
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Space and time!
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In aquatic systems, moisture is irrelevant ☺ but temperature, light, nutrients and a
variety of biological interactions remain important variables regulating species
distributions
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Microclimates
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Even with latitudinal/altitudinal considerations, there will be small spaces or patches in an
environment that have temperature, moisture, light, nutrient or other conditions
significantly different from the overall regime (e.g. a south-facing slope or sheltered ravine,
proximity to a creek, the shade of a rock or tree)
Similarly, a given aquatic site may have temperature, light or nutrient conditions that are
significantly different than the open water (e.g. upwellings or coral reefs in the ocean,
streamside vegetation in a river, sunken logs in a lake)
Specific conditions found in a localized area (patch) are referred to as its microclimate
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Microclimates II
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For animals, patchiness is also relative to the organism’s size and speed:
“Grain”
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biotic as well as abiotic factors structure ecosystems
1.Trophic relationships: predator/prey or foodwebs (producers, consumers, decomposers)
2.Non-feeding relationships (competition, symbiosis)
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The nature of relationships
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Don’t worry about the names of the interactions just yet!
Just note there are 3 possible outcomes
Both species benefit; only 1 species benefits but the other is unharmed; one benefits, the other is harmed
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Feeding relationships: food webs
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In spite of the variety and apparent complexity of foodwebs, they all have the
same underlying trophic pattern
Secondary (2o) consumers or carnivores (also heterotrophs)
Primary (1o ) consumers, grazers or herbivores (heterotrophs)
Producers, usually plants or autotrophs
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The relationship between producers and consumers is one we have seen before as
the carbon cycle
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Autotrophs (self-feeders) ‘feed’ themselves through photosynthesis (the process of turning inorganic carbon
into organic carbon and capturing energy)
CO2 + H2O <=> C6H12O6 + O2
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Heterotrophs (other feeding) ‘feed’ themselves by consuming organic carbon already fixed by autotrophs
and extracting its energy via respiration – that energy is then available for growth reproduction, etc.
(though they have to get rid of the CO2)
C6H12O6 + O2 <=> CO2 + H2O
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A heterotrophic web we often ignore is that of the “detritivores”
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Energy also helps us understand the limits of food webs
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The 2nd law of thermodynamics tells us that there will be an inevitable loss of “useful”
energy (or an increase in entropy) with the progressive movement to higher and higher
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trophic levels.
Eventually there will not be sufficient energy to support an additional trophic level.
Most ecosystems are characterized by 3 (terrestrial) or 4 (aquatic) trophic levels.
Thermodynamics also helps us understand the ecological consequences of ever increasing
meat consumption by humans
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‘Non-feeding’ relationships
Symbiosis
• Mutualism
• Commensalism
• Parasitism (are these just teeny-tiny carnivores?)
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non-feeding interactions:
symbiosis (mutualism)
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Mutualisms
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Speaking of mutualisms!
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non-feeding interactions: symbiosis (commensalism)
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Cool but complicated “commensals”
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non-feeding interactions: symbiosis (parasitism)
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Some parasites have little contact with their “hosts”
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Symbioses within symbioses
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Competition: Recall the wood warblers and the difference between their
fundamental and realized niches
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Why does it matter whether species compete for the same resource?
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There appears to be an “advantage” to “co-existing” or avoiding competition:
optimizing allocation of energy
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If an organism can avoid spending time competing with other organisms, it can spend more time (and
devote more energy) to finding a mate, reproducing and caring for young (increasing the chances that its
genes will persist into the next generation in the form of more offspring)
Perhaps at the expense of the organisms who spend more of their time competing
Similarly to Fig 3-11 (D&R): Rather than competing, these 5 species of warblers avoid
competition by partitioning their habitat or by “co-existing” (over long evolutionary time, each
has developed a unique approach to feeding)
The species of organisms we see coexisting today may be the result of competitive interactions that took
place thousands or millions of years ago (the ghost of competition past)
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Plants also exhibit strategies to avoid competition over nutrients, water, light or
pollinators (i.e. co-exist)
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Species of wood warblers or planaria or plants represent examples of avoidance of interspecific competition.
However organisms might also compete with other members of their own species (intraspecific competition)
with similarly negative results
Differentiation between larvae and adult, e.g. larval caterpillars and adult moths or butterflies, is assumed to
be a mechanism to avoid intraspecific competition
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Territoriality is another mechanism for avoiding intraspecific competition
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Over time (and assuming a reasonably stable environment), random genetic changes (mutations) could
confer on some individuals an increased ability to better exploit a narrower segment of the resource
gradient.
These individuals thus avoid niche overlap and potential competition (whether intra or inter).
IF this proves “successful” (i.e. the individuals with this characteristic leave more offspring than individuals
without the characteristic), then over time more and more individuals of that species will come to possess
the characteristic over time
The result is that the population will be ever more finely tuned to its environment!