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BIOL
4120
Principles of Ecology
Phil Ganter
320 Harned
Hall
963-5782
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The creature
above has 8 legs (note that is has lost one) but is not a spider
or a mite. What is it? |
Lecture 7 Animal Adaptations
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Objectives
Animal
Feeding
We need lots of terms to describe
all of the ways that animals get nutrition!
- feeding method can lead to changes
in mouthparts (dentition in mammals), skull shape (for animals with skulls),
and overall morphology
- terms often linked to taxonomy
of organism
Herbivory
- eating living vegetation - plant material is full of cellulose and usually
has relatively little nitrogen (found in proteins and nucleic acids) so it is
often a poor diet compared to carnivory.
- Cellulose
often not digested
- Some organisms digest it
with their own enzymes and some have Mutualistic
Symbionts that digest it
- Fermentation
in the gut often produces reduced compounds due to the lack of oxygen
- most important to us is Methane
(CH3),
a fermentation product in our and cattle guts that, because there are
so many cattle, is an important source of methane in the atmosphere and
methane is a greenhouse gas
- Vertebrates
- Browse
- feeding on woody vegetation, usually younger parts of plant are preferred
- Graze
- feeding on grasses and herbs
- Granivory
- feeding on seeds (many birds and rodents feed this way) - seeds are
rich food for plant material because they are storage for the embryonic
plant - often defended with thick, hard coverings or with toxins
- Frugivory
- feeding on fruit, usually high sugar but very low nitrogen
- Insects
- many insects simply eat the vegetation like a grazer but some feed in more
specialized ways
- Leaf
Mining - insects that enter the leaf and feed on the mesophyll
between the upper and lower epidermis
- Pit
Mining - small insects that dig pits on leaves and eat
the mesophyll in the region of the pit before leaving to dig another pit
- Phloem
and Xylem Feeding - some
insects have piercing - sucking mouthparts and can feed directly from
the transport system of plants. Aphids and leafhoppers feed from
the phloem (sugar rich) and cicadas feed from the xylem (a very poor food
source)
Carnivory
- feed on living animal tissue, generally eat high-quality food with a high
C:N ratio. Gut less specialized than herbivore gut.
Coprophagy
- feeding on faeces. Much undigested material leaves the gut along with
microbes resident in the gut. Organisms use this resource (dung beetles,
blow or bottle flies) and a few organisms (e, g, Lagomorphs - rabbits - and
pillbugs) eat their own faeces to extract more nutrients.
Fungivory
- feeding on fungi - often these are insects that feed on mushrooms (reproductive
structures) but also many soil organisms that feed on the mycelium
of the fungus, the net of hair-like hyphae
(chains of fungal cells) the constitute the body of the fungus. Many fungi
produce toxins to avoid being eaten.
Omnivory
- the ultimate non-specialist feeders that eat animal, plant or fungus and living
or dead. They often have little tolerance for particular toxins and must
eat materials that are not protected by toxins
- Filter
Feeding - a kind of omnivory employed by many sessile (fixed
in one place on a substrate like rock or a tree trunk) or sedentary (not likely
to move) animals. Filter feeders have a filter apparatus with which
they strain food particles of appropriate size from the air or water that
flows through the filter. Barnacles, clams, many marine invertebrates,
some aquatic insect larvae, and some spiders are filter feeders. Except
for the spiders (which are strict carnivores), filter feeders often eat whatever
they catch, living or not.
Saprophagy
- feeding on dead organic matter. Many bacteria and fungi are saprobes and,
if you never eat raw vegetables, perhaps you are too.
Detritivory
- these are the organisms that break down the leaves that fall on the forest
floor or that feed on the algae and animals that fall to the floor of a lake
or ocean. They can include fungi and bacteria plus the invertebrates
that chew apart the larger pieces.
Animal
Nutrition
Animals have more nutritional requirements
than plants (or fungi), which make the organic molecules they require.
Animals eat organic molecules and do not have the capability to synthesize many
of them.
- Essential Minerals
- much the same as plants
- Sodium can often be limiting
because (see lecture 5) it is first to leach from the soil and can be
scarce in the plants on which animals feed (dairy farmers make up for
this by putting salt licks, blocks of table salt, in pastures and deer
hunters know that this will also attract deer in some areas)
- Soils high in minerals are
sometimes eaten directly and places where they are exposed at the surface
act as natural Mineral Licks
for animals to make up dietary deficiencies (Butterflies sometimes
congregate on salty soil)
- Essential organic molecules
- Essential
Amino Acids - 14 of the 20 in animal proteins are essential
in animals, although the number varies among species of animal.
Remember that some amino acids can be converted into other amino acids
- Essential
Fatty Acids - many animals must have a source of particular
classes of fatty acid in their diet. Like amino acids, some fatty
acids can be inter-converted. Humans must have some kind of omega-3
and some kind of omega-6 fatty acids in the diet but can make all omega-3
varieties from whatever is in the diet.
- Vitamins
- - small organic molecules necessary but not synthesized - often act
as cofactors (working as part of a catalytic system) or coenzymes (transport
molecules like NAD). Number of vitamins varies with the species
(humans have 13 recognized at this time)
Many animals may get their essential
amino acids, vitamins, and fatty acids not strictly from their diet but from
mutualistic symbiotic microorganisms that live in their gut
or in their tissues
Many animals select food items based
on their quality
Carbon:Nitrogen ratio often explains
the preference - herbivores choose the plants with the lower ratio
Homeostatic
Adaptations
Animals expend energy and resources
to regulate the conditions prevailing internally
- Homeostasis
- the maintenance of relatively constant internal conditions in the face of
changing external conditions
- changing external conditions
are not a given - deep ocean organisms have a very constant internal temperature
(4° C) but this is because their environment is a constant 4 C
- To
Regulate - to hold a parameter within a range by responding
to variations from a set point in such a way as to increase the parameter
when is falls below the set point and decrease the parameter when it exceeds
the set point
- regulation comes about as
a result of Negative Feedback
- here we have to define it a bit differently than the standard definition
(which is simply when the output of a system acts as a signal that reduces
the output of the system according to its magnitude - more output reduces
the output more)
- for regulation, negative
feedback is when the output of a system is compared to a set point and
the sign of the difference between the output and the set point acts as
a signal that causes the system to react in the opposite way (if the sign
is negative, then the system reacts positively, and, if positive, the
system reacts negatively)
- In this section, we are concerned
with how individual animals regulate internal parameters (focus on temperature
and osmotic balance) but regulation will also be the focus when examining
processes at the population level (is the population size regulated or not?)
and at higher levels (is nitrogen flow regulated? does a forest regulate
its temperature?)
- Homeostatic
Plateau - animals usually do not keep a parameter at the exact
set point but within a range of values around the set point. The range
is the homeostatic plateau
Temperature
homeostasis
Animals are:
- Endotherms
- generate their own heat in an attempt to maintain a constant temperature
internally
- Ectotherms
- gain heat from the environment and either do not regulate their internal
temperature or do so through choosing environments with the proper temperature
(like a snake sunning itself on a rock in the morning when the air is
too cool)
- Homeotherms
- these are animals that have a constant internal temperature and almost
all are also endotherms because the internal temperature is higher than
the environmental temperature
- Poikilotherms
- animals that experience a wide range of internal temperatures, usually
a range set by environmental variation in temperature
- Poikilotherms may not
be active at all temperatures but have an Operative
Temperature Range
- Poikilotherms often take
advantage of Microclimate
differences to keep their temperature within the operative temperature
range
- Heterotherms
- animals that only regulate their internal temperature for part of the
body or for part of the time. They usually employ endothermy to
achieve the homeothermic portion of their body or their lives
- Some fish, like tuna,
may regulate temperature (be homeothermic) in some muscles but not
in other portions of their body
- Some cicadas are homeotherms
only when singing or flying but may spend much of the day as poikilotherms
- Some organisms (bats,
bees and hummingbirds) have a set point for temperature that depends
on their activity - high for active flight and low (near environmental
temperature) when resting
Acclimatization
- process of changing the set point in response to external conditions
- Many animals (and plants)
are able to change their physiology to match external conditions
- Fish in a winter lake are
active at a temperature that would be too cold for activity during the
summer months (i. e. their winter operative temperature range is lower
than summer operative temperature range)
Body size and Temperature Regulation
- Endothermy/Homeothermy
- Small animals have a larger surface area
to volume ratio than large animals
- Heat is lost across the surface area
so small animals lose heat faster than large animals
- To maintain homeothermy is a greater
cost in terms of energy production for a small animal than for
a large animal
- Torpor
- the cessation of temperature regulation for a period of time, allowing
body temperature to reach environmental levels and reducing the rate
of activity
- common in small organisms
that reduce the energy expended on heat by becoming torpid for part
of the year or part of the day
- flight muscles in birds
and insects often have high optimal operating temperatures and hummingbirds
and some insects that hover in flight become torpid when resting to
save energy
- Ectothermy/Poikilothermy
- Large animals take longer
to absorb heat from the environment and find it harder to use the
environment to regulate their temperature
- No really large poikilotherms
(assuming that dinosaurs were homeotherms)
- For terrestrial vertebrates,
larger poikilotherms found in warm climates (largest snakes are tropical,
crocodilians are tropical or subtropical)
Specific adaptations
- Countercurrent
Heat Exchange- using flow in the opposite direction to
change temperature (or O2
concentration) in blood rapidly
- Blood in vessels in extremities
(hand, head, foot) cools in homeotherms
- As the blood flows back
into the body, it will cool the body
- Countercurrent flow places
the veins returning the blood to the core of the body near the arteries
carrying warm blood from the core out to the extremity
- as hot blood moves out
it constantly flows next to cool blood coming in the opposite direction
and loses heat to the cooler blood
- thus the heat from the
core is used to heat up the returning blood and is not lost to the
environment
- Rete
Mirabile - a "wonderful net" of blood vessels
that take advantage of countercurrent flow to help regulate a specific
organ's temperature
- Hibernation
- seasonal torpor accompanied by physiological changes to the basic metabolic
rate
- Supercooling
- by secreting Antifreeze Compounds into the blood and body fluid, some
animals are able to keep their bodies from freezing even though they drop
below 0° C
Water
and Solute Balance
Water poses different problems
for animals in different environments and so we will divide this section
between land and sea
- Terrestrial animals -
- gain water by drinking,
eating (as part of food) or metabolic water from cellular respiration,
dehydration syntheses and other reactions
- lose water through evaporation, exhalation
of moist air from lungs, and urine
- adaptations to arid environments
- Dormancy
for driest part of year
- migration away during dry periods
- Nocturnal
Activity
- concentrate urine
- produce uric
acid rather than urine (which is a urea solution)
- Tolerance
of low water content in tissues
- loss of water also brings problems
in solute balance
- salt gland (in some birds and
reptiles) excretes salt to maintain balance
- Aquatic animals - problems
are related to osmotic balance
- Marine - relatively constant
salt content
- many invertebrates are isotonic with
marine environment and
- some fish (sharks and relatives)
are isotonic and adjust their tonicity using urea
- Bony fish (Osteichthyes)
are hypotonic to ocean water and must constantly drink water to
balance loss of water
- water they drink is salty and
so they excrete excess salt through the kidneys and by pumping
the salts through the gills
- glomerulus of kidneys modified
to process lots of water
- Freshwater
- all animals are hypertonic compared
with fresh water and must cope with the influx of water
- Bony fish (Osteichthyes)
have to produce copious amounts of urine to balance the influx
of water
- Gills actively take up salts
to balance salt loss through kidneys
Buoyancy
in Aquatic Animals
Aquatic organisms often maintain
their position in the water column by becoming as dense as the water a the appropriate
depth (water becomes denser as temperature decreases)
Unless they actively swim, aquatic
organisms will move up or down in the water until their density matches the
water's density - where they are said to be Neutrally Buoyant
In general, all organisms have areas
of their body that are denser than water and so they must adjust overall buoyancy
by having some areas less dense than water to balance out average density
- Lipids are less dense, so lipid
bodies (from drops in single-celled algal cells to blubber in seals and whales
to lipid-rich livers in some fish) can be used to adjust buoyancy
- Osteichthyes
(bony fish) have Swim Bladders
(O2 filled organs)
that can be rapidly made larger or smaller to allow the fish to move to different
depths quickly without having to fight to maintain their position
Responses
to Daily and Seasonal Cycles in the Environment
There are many natural phenomena that
occur in a cyclical manner. Animals have adapted to take advantage of these
natural cycles
Circadian
and Tidal Cycles
- Light and temperature cycle daily
and animals adjust their active periods and metabolism to these basic cycle
- Internal Biological
Clock
- common to all animals, from protists
to us
- nervous system function in organisms
with nervous systems
- important for animals that prey
on animals with daily activity cycles or that pollinate flowers that open
only during day or night
- tidal cycle important for animals
in estuaries or in intertidal zone so that they are prepared for inundation
and exposure to air
Seasonal
Cycles
- Animal responses are often linked
to the ability to perceive the changes in daylight length
- can trigger changes in activity
- can initiate the reproductive
cycle
- Critical Daylength
- the duration of day (or night)
that triggers a particular response
- Short
Day - response is triggered when day is shorter than some
critical value
- Long
Day - response is triggered when day is longer than some
critical value
- can either be how long the
day is or how long the night is
- Diapause
- short day response in some temperate insects - change their activity
and metabolic rate to facilitate overwintering
- can happen in adult, juvenile,
or even egg stage of life history
Terms
Herbivory, Cellulose, Mutualistic Symbionts, Fermentation,
Methane, Browse, Graze, Granivory, Frugivory, Leaf Mining, Pit Mining, Phloem
and Xylem Feeding, Carnivory, Coprophagy, Fungivory, Mycelium, Hyphae, Omnivory,
Filter Feeding, Saprophagy, Detritivory, Essential Minerals, Mineral Licks,
Essential Amino Acids, Essential Fatty Acids, Vitamins, Homeostasis, Regulate,
Negative Feedback, Homeostatic Plateau, Endotherms, Ectotherms, Homeotherms,
Poikilotherms, Operative Temperature Range, Microclimate, Heterotherms, Acclimitization,
Torpor, Countercurrent Heat Exchange, Rete Mirabile, Hibernation, Supercooling,
Dormancy, Nocturnal Activity, Uric Acid, Tolerance, Osteichthyes, Swim Bladders,
Circadian Cycle, Tidal Cycle, Internal Biological Clock, Critical Daylength,
Short Day, Long Day, Diapause
Last updated January 25, 2007