BIOL 4120

Principles of Ecology

Phil Ganter

320 Harned Hall


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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Overview - Link to Course 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


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