Organisms interact with each other in a variety of ways.  These interactions can be cooperative, antagonistic, defensive, reciprocal, harmful, communal, opportunistic, beneficial, or neutral.  Symbioses encapsulate the relationships that different species of organisms have with each other: the good, the bad, and the ugly.  These interactions typically fall into one of three categories: mutualism, parasitism, and commensalism.

Some symbioses are obligate (necessary); this means that the organisms depend on each other for their survival.  In many cases this co-dependency has occurred over time as each organism adapts to the benefits of depending on each other.  Other symbioses are facultative, which means that they are not absolutely necessary for the survival of either organism.  Some symbiotic relationships are timeless, and species-specific examples persist in the biological literature.  Some of these include clownfish and sea anemones, fleas and dogs, and sharks and remoras.  Facultative symbioses are more loosely-associated relationships and not always formally recognized.  For example, there are many tiny insects that live in bird nests.  These insects consume waste that the birds produce, keeping the nest clean and decreasing the chance for the build-up of bacteria and disease, they get a free meal from the birds and the birds get free house-cleaning services.  These types of interactions are indirect and occur in nature in various capacities, many times going unrecognized.

Ectosymbiosis occurs when symbionts (members of the symbiotic relationship) interact with each other in an open environment, like hummingbirds and trumpet flowers.  Endosymbiosis occurs when one symbiont lives within the body of another, which is the case with internal parasites like liver flukes and tapeworms.

There is a little bit of contention as to what the idea of symbiotic relationships actually encompasses.  Some scientists believe that symbioses should only describe persistent interactions among organisms that remain over time.  Others feel that any type of interactions fall into this category.

Mutualism

A mutualistic relationship is one in which both organisms benefit from interacting with each other.  They cooperate with each other to achieve a desired outcome that will be beneficial to both of them.  Take the wrasse in the video clip for example.  Cleaner wrasses have a mutualistic relationship with the large fish they service.  The fish at the cleaning station line up to get the parasites picked off them; they are cleaned and free from harmful, blood-sucking parasites and the cleaner wrasse gets a nice meal from the fish.  There are certain species of ‘cleaner’ shrimp that also perform this function.  Both get something useful out of the deal, so the relationship is mutually beneficial.  Same thing is true for oxpeckers and antelope, and certain apes like baboons and chimps that comb each other’s fur for ticks and lice.  One gets a meal, the other gets cleaned.

Most animals are not capable of digesting cellulose, a material found in plant tissues, yet many animals eat plants.  How are they able to do this?  The answer is mutualism.  Animals that eat plant matter house bacteria and protists in their digestive systems that are capable of breaking down the cellulose in the plant material they consume.  Animals with different diets require different microorganisms to break down these tissues. Grass-eating cows for example host a different set of bacteria than wood-eating termites.  In this kind of relationship the host provides a warm, safe place for the microfauna to live while providing a free source of nourishment and in turn for providing that food and shelter, they reap the benefits of metabolic services.

Mutualism occurs in the plant world as well, with pollination being the primary example of mutualistic plant-animal relationships.  Some more mutualistic symbioses for you to explore: honey badgers and honeyguides, ants and butterfly caterpillars, zooxanthelles and coral.

Obligate Co-dependency

In mutualistic relationships, organisms are intimately involved in each other’s personal space; most of the time they are in direct physical contact.  Some organisms are so close to their mutual beneficiary, and have evolved with them for so long, that neither of them could exist with much success independently.  Take lichens for example- the colorful, flaky, fleshy, sprouty, crusty-looking growths we see ‘growing’ on trees and rocks. These ‘organisms’ are actually a symbiotic relationship between a fungus (a mycobiont) and an autotrophic (photosynthetic) organism (a photobiont, usually either a green alga or a cyanobacterium).  These organisms do occur independently in nature, but when they come together to form a lichen, their physiology and morphological structure changes drastically.  Individually, green algae and cyanobacteria can survive just fine, but the delicate fungi do not fare so well alone.  In this relationship the fungus ‘cultivates’ the autotrophic photobiont by encapsulating it and performing tiny-scale agriculture.  The photosynthetic partner uses the sun’s energy to produce food for both organisms, and in turn, the fungus retains water and provides a large surface area from which the photobiont can absorb nutrients.  These individual components are so small, that when joined together they give the appearance of a single organism.

When the ‘body’ of a lichen is separated, you can see the two organisms independently.  If you have a microscope here is a fun experiment to try:

HOW-TO Symbiont Soup

You will need:

• Small amount of lichen (a teaspoon full)
• Microscope
• Clean glass slide
• Mortar and pestle
• Dropper or pipette
• Water

Directions:

• Collect some lichens from around your home or classroom
• Grind them in the mortar and pestle, adding enough water to make a slightly soupy mixture
  Collect a drop or two of the mixture in the dropper and place it on the glass slide
• Observe your soup under the microscope

What do you see? Can you tell which organism is which?

Some more obligate mutualistic relationships to explore: Portuguese man-o-war, European mistletoe, plant roots and mycorrhyzal fungi.

Parasitism

Parasitism is a relationship in which one organism benefits and the other is harmed.  Parasitic interactions consist of a parasite (the organism doing the harm) and a host (the organism being harmed).  In most cases, the parasite is smaller than the host.  Parasitism is especially prevalent in the micro-faunal world.  There are thousands of species of ticks, mites, leeches, chiggers, worms, mosquitoes, viruses, and bacteria that literally feed off their hosts.  In many cases, parasitoids are host-specific, and as a result have undergone amazing evolutionary changes to co-evolve with their hosts.  Although parasitism involves the pilfering of resources from one organism to another, it is in the parasites best interest not to completely debilitate its host, otherwise it will deplete its source of nourishment.

Types of Parasitism

When it comes to parasites, most people think of the blood-sucking arthropod variety, but there are many other different types of parasites, and many different ways that organisms weasel resources away from each other.

Brood Parasites

Take the brown-headed cowbird, a seemingly harmless creature common in woodlands and suburbs across America.  This cunning little critter is a brood parasite.  Female cowbirds lie in wait for unsuspecting female passerines (perching birds) to leave their nests and move in to lay an egg in her nest while she is gone.  When the resident female returns, she doesn’t know what hit her and spends her time and energy brooding the intruding egg along with her own.  Once the eggs hatch the mother cares for all the babies, even the uninvited orphan.  Oftentimes the cowbird grows faster and stronger than the resident hatchlings and can out-compete them in the nest, but the mother bird is devout and cares for it nonetheless.  By parasitizing the passerine’s nest, the female cowbird ensures that her offspring are cared for with minimal energy expenditure on her part.  While she doesn’t take anything directly from the mother bird, she is indirectly parasitizing her energy and resources.

Food Parasites

Parasites can parasitize an animal’s energy, directly by consuming their body fluids, and indirectly by placing an energetic burden on them.  That’s pretty bold, but some animals take bold to an even greater level.  There are some creatures in the animal kingdom that will literally take the food out of another’s mouth!  The parasitic jaeger, a predatory seabird, makes a habit of stealing food.  They soar around while terns and other seabirds are fishing and chase them in the air to try and steal their food.  Sometimes they are successful in capturing the food right from their mouths, but in most cases they harass the hunters so much that they tire and drop the food and the jaeger scoops up a free meal.

Commensalism

A commensalistic relationship is one in which one organism benefits and the other organism is unaffected, meaning it is neither harmed nor benefitted.  The classic example of commensalism is that of sharks and remoras.  Remoras are scavenging fish that cruise around with sharks.  Sometimes they swim alongside sharks, and sometimes they hitch a ride, attaching themselves via a suction-cup like appendage on their dorsal (top side) surface.  The remoras wait for the sharks to make a kill, and when they do, snap up bits and pieces of the bloody, shredded flesh as the shark tears into it.  They don’t pose any threat to the sharks, and don’t take the food from them, merely eat the scraps.  One could argue, however, that when the remoras attach themselves to the shark, they create drag, which makes the shark have to work harder and expend more energy to get around, thus the remora is indirectly parasitizing the shark.  While the drag the remora creates might be minuscule, the reasoning behind the theory is valid.

Another example of a commensalistic relationship is between cattle and cattle egrets.  Cattle egrets are frequently found in fields foraging alongside herds of cattle.  While the cows munch away on grass, they stir up insects which the egrets snap up.  This may be more reflective of a truly commensalistic relationship as the egrets pose no real impediment to the cattle (or perhaps the cows have to expend more energy to watch where they are going to avoid stepping on the egrets!).

The Big Picture

Symbioses are a dynamic way in which organisms of different taxa interact with each other.  These relationships can be positive or negative depending on their nature and the extent with which the organisms are involved with each other.  Below is a simple table to visualize the types of interactions that symbiotic relationships between organisms embody.

*n=neutral

It’s a struggle, a fight, two entities opposing each other for a desired outcome. We see the forces of competition at work in our everyday lives- feuding political parties, commercial product markets, rivaling athletics. Competition happens when two parties want the same thing, but there isn’t enough of it to go around…so they compete for it.

What Do Organisms Compete For?

Organisms compete for the resources they need to survive- air, water, food, and space. In areas where these are sufficient, organisms live in comfortable co-existence, and in areas where resources are abundant, the ecosystem boasts high species richness (diversity). The more generalist an organism is, the better chances it has to co-exist with its conspecifics (other members of the same species) and other taxa. Animals and plants that have specific life history requirements, like cavity-nesting birds, plants with ph-specific soil requisites, or animals with obligate feeding behaviors, have a more difficult time competing. These resources can be limiting factors for where organisms are distributed, and competition for them can be fierce.

Types of Competition

A fundamental concept in ecology is the competitive exclusion principle. This states that two species with similar ecological niches cannot exist sympatrically (in the same environment). One will always out-compete the other, so the more competitive species will stay and the subordinate one will either adapt or be excluded (by either emigration or extinction). While competition in the natural world is eminent, it doesn’t always happen in the same way.

Interspecific competition is when different animals that live in the same geographic area (sympatric species) compete for the same set of resources, mostly food and space. Intraspecific competition is when different species compete with each other, usually for more specific requirements like mates and nesting/denning sites. Direct competition occurs when individuals compete with each other directly for the same resource, ie: two bull moose battling for access to a single female. Indirect competition occurs when organisms use the same resource, but don’t necessarily interact with each other- for example, diurnal cheetahs and nocturnal leopards using the same waterhole in a grassland savanna. Interference competition is when there is a deliberate displacement of individuals by their competitor. The less competitive individuals are forced to go elsewhere to find resources. Studies have shown, however, that if the more competitive animals leave, the displaced individuals will return. Exploitation competition is more subtle. This occurs when a species’ survival or reproduction is suppressed because of the presence of a staunch competitor. There is no actual displacement, as the competitive pressure manifests itself through a reduction in an individual’s ability to survive and reproduce.

Forces of Competition

Defensive Behavior

When an animal has found a space that contains all the resources it needs to survive, it wants to hold on to it. This is why many animals are territorial; they defend their territory which contains those resources. Animals defend territories for many different types of resources: a convenient source of fresh water, an ample supply of vegetation, proximity to a stable source of prey, denning sites, etc. Animals advertise their ownership of these territories by visual and chemical signals that deter their competitors from encroaching on their turf. If these signals are ignored, and the boundaries of the territory are breached, a territorial battle is sure to ensue.

Aggressive Behavior

Animals exhibit aggressive behavior when one of their resources is compromised. Males may compete over an existing territory, available females, nesting sites, or breeding rights in a social hierarchy. Defensive behaviors often lead to aggression if problems can’t be sorted out through threatening displays or intimidation. In most cases, animals would prefer to avoid antagonistic encounters because it requires a huge expenditure of energy to participate in an aggressive interaction, but the resources they are aiming to protect are vital enough that they are willing to risk it if necessary.

Competition of the Herbivorous Kind

Competition isn’t just a phenomenon in the animal world; plants compete with each other too. They need adequate sunlight, soil nutrients, and fresh water to survive. Though they are stationary, they still have ways of combating each other. Over time plants have evolved ingenious ways of procuring sunlight, attracting pollinators, and obtaining fresh water. They may take an offensive approach, responding to the competition head-on, or a defensive approach, making modifications to increase their chances of survival and reproduction. For example, when sunlight is the limiting factor, some forest trees grow rapidly to tower over their competitors and absorb the most sunlight, others channel their energy into producing many seeds and attempting to spread them so that they increase the chances of their offspring landing in a well-lit area. Plants have developed all kinds of competitive strategies from storing nutrients to becoming parasites to developing disease resistance.

How to Avoid Competition- Isolate Yourself

Nature is am amazing beast; it has mechanisms in place to allow species to exist in the same place at the same time using the similar resources. This is the beauty of niche separation and is the answer to the competitive exclusion principle. Different species have different life requirements, eat different foods, live in different habitats, and behave differently, all in the name of sharing resources. Sometimes, however, there is just no way around it, organisms have to share the same resources, and in this instance, nature has the uncanny ability to adapt. So if you’re an animal or a plant that can’t hack the competition, your best bet is to avoid it, and plants and animals have developed some pretty clever ways to isolate themselves from each other.

Geographic Isolation

One method of isolation is geographic isolation- not being in the same place at the same time. Animals that are geographically separated have a better chance of obtaining the resources they need. This isolation can occur through animals having different geographic distributions or by participating in seasonal migrations. Geographic separators might be an expanse of land, a mountain range, a body of water, or an elevation gradient.

Behavioral Isolation

This occurs when animals have contradictory behaviors that prevent them from competing with each other. For example, by day, birds rule the air. They forage, maintain territories, reproduce, and compete with each other for the best available resources. By night, however, bats rule the roost. Come dusk there is a taxonomic tango when the diurnal (active by day) organisms retire for the evening and the nocturnal (active by night) organisms commence their daily follies. By the cover of night nocturnal organisms avoid competitive interactions with their diurnal counterparts. In some ecosystems, the nightly taxonomic exchange is quite the spectacle. Certain night-blooming flowers open their blossoms to be pollinated by bats. Insects emerge to forage after spending the day avoiding hungry birds.

Foraging habits are another way that organisms can avert competing with each other. Take raptors for example. A red-tailed hawk is a generalist predator; they eat anything from rodents to reptiles to other birds. They are good competitors with other birds of prey because they consume a wide variety of prey so their options are many. Specialist predators, however, like the osprey, which eats strictly fish, are limited in their prey selection as well as their geographic range because they have to live in areas where their prey resides. Take two similar animals then that inhabit the same geographic area and eat the same type of food…what then? Herbivorous rhinos deal with this conundrum by consuming different parts of plants. White rhinos have flat, wide lips for grazing grasses while black rhinos have pointed, dexterous lips for browsing shrubs.

Mechanical Isolation

The lip morphology of rhinos is an evolutionary expression of a behavioral trait that separated rhinos long ago. Today there are many animals that have morphological differences that directly allow them to avoid competition with other organisms. Like giraffes who’s browse line is way above that of the other browsers it resides with, and hyenas whose jaw structure and musculature is strong enough to consume the hides and bones of carcasses left behind by other predators. Sometimes isolation mechanisms influence each other, adding another impediment to competition. Organisms that have been geographically separated for long periods of time can evolve morphological and behavioral changes that prevent them from breeding with each other.

All these methods of isolation are changes that have occurred over many generations. Organisms have evolved over time to avoid competition and the changes have become incorporated in their life histories. The most awesome thing about evolution is that it never stops! As the environment changes and new stressors are added to an ecosystem, that pressure influences organisms to change, thus making them better competitors.
Competition plays a very important role in ecology and evolution. The best competitors are the ones who survive and get to pass on their genes. Their progeny (offspring) will have an increased chance of survival because their parents out-competed their conspecifics. The best competitors have the best fitness, which is a measure of the genes that are passed on to succeeding generations. So the best competitors are the best survivors, which have more offspring, which means that more competitive genes are perpetuated in the gene pool. It is important to note that these changes occur over very long periods of time and the life history characteristics of organisms we see today are the results of changes that happened over millennia.

The Trade Off

These rewards are not without consequence. Sometimes being a good competitor in one area means that you are lacking in another. Take Australian lyrebirds for example. They have long, beautiful tail plumes as ornaments to attract female mates. The longer, more colorful their feathers are, the better competitors they are among other males, but this also means that they are more conspicuous. A colorful bird with long, elaborate feathers is not hard to miss, particularly when he is dancing and calling to attract a mate. The very characteristics that make him a good competitor among his male counterparts are also a detriment to him as they also attract potential predators. The question then becomes…is advertising for female mates worth the risk of being discovered by a predator? What do you think?

According to the ‘closed community concept’ in the world of bird behavior, established communities are one way to avoid competition. For example, when an aggregation of birds can successfully co-exist without significantly compromising each other’s ability to acquire resources, they prefer this stability. By maintaining the community they resist invasion by other potential competitors. Communities can be made up of a single species, or there can be mixed species colonies.

Mixed seabird colony- great crested terns and brown boobies
Kia Island, Fiji

 

Competition as a Regulator

When two organisms or populations compete with each other, whether it be directly or indirectly, one of several outcomes can be expected. In extreme cases one population (or individual) out-competes the other and the ‘losing’ organism becomes extinct from the area. If, however, the competition event is spread over time and the losing animal has time to respond and recover, they may relocate to another geographic area (emigrate). If the losing organism is not displaced, it may change its behavior or requirements to utilize different resources so that it is no longer in competition with its opponent.
Intraspecific competition can serve as a regulator for population size. If a particular source of prey, or abiotic habitat feature is not readily available, then competition for the ones that are will be heavy. If the requirements are scarce enough, this will cause the population to remain stable, or decrease. If resources are readily available, then competition will be low and a population may increase.

Foreign Contenders

Sometimes competition can have a serious impact on an ecosystem, especially when invasive or exotic species are involved. When non-native organisms colonize a new area, they are sometimes better suited to compete with native organisms for resources. Once able to overcome the transition of the relocation, they can become very successful and out-compete native organisms, causing their populations to decline, or in extreme cases, become locally extinct.

Human Competition

As the human population continues to increase, humans are in competition with nature. Our requirements for survival are just as basic as those of plants and animals. We breathe the same air, drink the same water, and use the same space. Fortunately for us, we have intellect, which is the greatest competitive advantage to be had. We can use our brains to build tools and technologies that make us seemingly undefeatable. Unfortunately for us, our utilitarian attitude has cost us millions and millions of acres in forests, wetlands, coral reefs, and other precious habitats around the globe. While we might not be directly competing with plants and animals for food or potential mates, we are indirectly competing with them by consuming space, and while our population is increasing, theirs are declining.

Humans directly compete with animals also; a prime example is the global overfishing conundrum. Oceans world-wide are experiencing massive declines in fish populations due to human over-harvest. Commercial fishing operations are way better suited to fish for prized commercial fish like tuna, cod, salmon, and crustaceans like shrimp and lobster. People out-competing natural predators means that we are taking too many, too rapidly, and populations of predator and prey are suffering.

The Big Picture

Understanding competition is a huge component of ecology. The way organisms compete with each other determines species distributions, population dynamics, community structure, food webs, and social dominance hierarchies. Competitive interactions over time manifest themselves in physical and behavioral adaptations that shape the evolution of a species. Human activity, invasive species, climate change, and environmental pressure are constant stressors on ecosystems, making resources less available and of less quality. These stressors affect the way that organisms compete with each other and their ability to survive and co-exist.

Even Dr. Seuss Understood the Complexities of Competition

And NUH is the letter I use to spell Nutches,
Who live in small caves, known as Niches, for hutches.
These Nutches have troubles, the biggest of which is
The fact there are many more Nutches than Niches.
Each Nutch in a Nich knows that some other Nutch
Would like to move into his Nich very much.
So each Nutch in a Nich has to watch that small Nich
Or Nutches who haven’t got Niches will snitch.

Dr. Seuss – On Beyond Zebra (1955)

Questions to Ponder???

If an animal in a given habitat has a similar ecological niche to another species, how would direct competition influence their interactions?

What possible outcomes could there be if an exotic species is accidentally introduced to a stable, mixed-bird community?

Can you give an example of another way that humans compete with nature?

Predation

Simply put, predation (or carnivory) is a feeding strategy in which animals consume other animals. In this strategy predators are the hunters and prey are what they hunt. Predators can be fierce hunters like tigers and eagles and sharks, or they can be small and unassuming like dragonflies, bats, and moles. Predation occurs in all phyla of Kingdom Animalia. Everything from the very primitive protozoans to the highly-evolved mammals predate each other.

Animals that eat other animals have simple digestive systems because the majority of what they consume is protein tissue which is easily broken down. Their digestive tracts are short and they lack the organs needed to process plant material.

Some examples of animals with carnivorous feeding habits include: lions, tigers, pumas, wolves, eagles, hawks, owls, snakes, dolphins, otters, jaguars, ocelots, jackals, falcons, crocodiles, platypuses, hedgehogs, orcas, caracals, lynx, polar bears, weasels, Tasmanian devils, wolverines, and many species of fish and invertebrates.

What is a Carnivore, Exactly?

Most people think of carnivores as any animal that eats meat. This is partly true. In a feeding strategy context, carnivores are animals that eat other animals. This would make bobcats, alligators, and hawks all even on the same playing field. Taxonomically, however, only certain types of animals belong to the order Carnivora, which is a mammalian taxon. So taxonomically speaking, mammalian members of the order Carnivora are the true carnivores. Members of this order are separated into two groups, feliform (cat-like) and caniform (dog-like). The feliform groups include, of course, felids (cats), herpestids (mongooses and civets), hyaenids (hyenas), and viverids (genets and civets). The caniform group is composed of canids (dogs), ursids (bears), procyonids (raccoons), mustelids (skunks, weasels, and otters), and pinnipeds (seals, sea lions, and walruses). The characteristics that these animals have in common are protein diets, expanded brain cases, an excellent sense of smell, and large canines and specialized shearing teeth.

Types of Predators

While we typically think of ‘carnivores’ as meat eaters, there are many different types of carnivores that consume protein matter from a diversity of sources. Below is a list of different types of feeding strategies for meat eaters:

• Sanguinivore- blood eaters (ie: vampire bats)
• Piscivore- fish eaters (ie: loons)
• Insectivore- insect eaters (ie: hedgehogs)
• Avivore- bird eaters (ie: falcons)
• Scavengers- carrion eaters (eating dead animals) (ie: vultures)

Morphology of a Predator

There is a diverse array of predators in the animal kingdom, each with their own special physical characteristics, but they all have certain body structures in common. Predators have sharp teeth (or beaks) for biting, gripping, and tearing flesh and claws for grasping, stabbing, and shredding.

• Claws/Talons: Sharp and dexterous for grasping, holding, pinning, and shredding

• Beaks: Sharp and hooked for tearing and shredding

• Teeth: Pointed and sharp for biting, grasping, ripping, and chewing
• Skull: Strong and robust with large areas for muscle attachment to support strong jaws
• Body structure: Robust, powerful, flexible, and specially-suited to the type of predation

Predator Strategies

Most predators are hunters (some are scavengers), and if they are to be successful hunters, then they must be skillful. Different types of predators have developed different strategies for hunting their prey, and different species of predators are grouped into taxonomic categories depending on some of those strategies. Take wolves for example. Wolves are canids, members of the dog family; they are very social creatures and as such hunt socially, in packs. In pack hunting, every member of the pack has a special job to do; some animals herd the prey, some keep a lookout, and some make the kill. Once the prey has been captured, the wolves feed according to their social hierarchy with dominant animals feeding first, followed by high-ranking adults and so on. Each member of the pack plays a different role in making the kill, but no one is more or less important than the other. It takes the entire pack to take down the prey.

Now take leopards, felids, members of the cat family. These animals have a very different style of hunting. These solitary hunters are silent stalkers. They stealthily stalk their prey to a close enough distance, and then pounce on it. This is just one felid strategy. The cheetah is a speed demon. Its hunting strategy is to run its prey down. Cheetahs are capable of reaching speeds up to 70pmh for short distances but can run at 40mph for miles. Once they have closed in on their prey, they chase it until it can’t run anymore, then they knock it off its balance with one swipe of an agile paw and its game over. Tigers are ambushers. Servals are pouncers. Different species of felids have different strategies of capturing prey, but the one thing they have in common is they all do it independently. There is one exception to this rule. Can you think of which well-known cat does not fit the typical felid, solitary hunting strategy? (Hint: it lives in Africa and some parts of the Middle East).

Some animals that may not be particularly strong or stealthy compensate for their lack of agility by using chemical aids. Take this banded sea crate for example. While seemingly harmless, this guy packs quite a punch. He faces the compounded challenge of hunting fish in the water, not an easy quarry. So in order to help his hunt, he uses special chemicals in his saliva to paralyze fish so once he catches them in his jaws, they can’t escape. And he’s not messing around; the venom in his saliva is potent enough to kill a human being! Another reptile that uses chemical aids is the fierce Komodo dragon. While colossal for a lizard, these guys typically hunt prey much larger than themselves. So to compensate for their smaller size they have a deadly poison in their saliva that slowly debilitates their prey. They attack the animal, delivering a deadly bite, then wait quietly nearby as the animal slowly dies. Once they know the animal is too weak to fight back, they go in for the final kill.

Herbivory

Herbivores eat plant material, which is much more difficult to digest than animal tissue. The nutrition of plants is locked up inside rigid cell walls and contains many molecules that are difficult to digest. Herbivores deal with this conundrum by having complex digestive systems that can tease apart plant tissues and extract the nutrition inside. But even with this powerful digestive system, plant material is still not as high in fat and protein as animal tissue, so herbivores have to eat a lot to maintain their bodies. Animals that eat the most nutritious parts of plants (nuts, seeds, and fruit) can get away with eating a modest amount, but animals that eat low-quality plants or parts of plants (grass blades, bark, leaves) have to eat an enormous amount to stay healthy. Take an adult African elephant for example. In order to maintain its body weight and keep up with all its bodily functions, it has to eat over 100 pounds of vegetation a day, even more when its mating/breeding season.

Herbivory Examples

Some examples of animals with herbivorous feeding habits include: zebras, wildebeests, antelope, deer, rhinos, hippos, gazelles, sheep, goats, cattle, giraffes, elephants, moose, alpacas and llamas, rabbits, beavers, camels, horses, manatees, sloths, tapirs, okapis, reindeer, musk oxen, bison, buffalo, and iguanas. Below is a list of different types of feeding strategies for plant eaters:

• Granivores- grain eaters (ie: some rodents)
• Graminivore- grass eaters (ie: zebra)
• Frugavores- fruit eaters (ie: flying foxes)
• Foliovores- leaf eaters (ie: koalas)
• Nectivores- nectar eaters (ie: hummingbirds)
• Palynivore- pollen eaters (ie: some insects)

Which Type of Fermenter are You?

Hindgut fermenters have a single, simple stomach. They digest plant material with the help of bacteria that live in their digestive system. Fermentation takes place primarily in the cecum (tissue pouch where bacteria live) and large intestine. Examples of animals that use this type of digestion are zebras, horses, rhinos, tapirs, rodents, rabbits, and pikas.

Foregut fermenters (ruminants) have a complex, four-chambered stomach. These animals can actually
digest cellulose without the help of bacteria, using their high-tech stomach. After they chew and swallow their food, it’s sent down to be partially digested, then, when the animal is resting, it regurgitates the food in the form of a cud (ball of chewed grass) and chews it again to break it down further.

Energetically speaking, foregut fermentation is more efficient than hindgut fermentation, but there are benefits and drawbacks to each strategy. While usually bulk-eaters, hindgut fermenters have the ability to get more out of eating small quantities of food as opposed to ruminants. Ruminants can digest cellulose more effectively, but are limited to areas where the quality of forage is higher than what hindgut fermenters could survive on.

Obligate Herbivory

Some herbivores have become so specific in their food habits that their bodies have developed special strategies to process their food. Take the koala for example; it exclusively eats eucalyptus leaves which are low in protein and high in indigestible materials. It’s very specific diet is likely an evolutionary response to a high availability of a food that other animals were not eating. Since the food was readily available and abundant, the koala took advantage of it, and its body responded by developing special ways to process this unique food. This phenomenon is also observed in other herbivores like pandas and sloths. If you notice, the things these animals have in common are a low metabolic rate and extensive periods of rest during the day…another adaptation to a nutrient-poor source of food.

Omnivory

Omnivores are the middle ground of the two extremes of predation and herbivory; they eat both plant and animal matter. From a survival standpoint, this really is the way to go. Animals that consume both types of food have more sources of food available and can capitalize on one if the other is scarce.

Some examples of animals with omnivorous feeding habits include: coyotes, bears, raccoons, wild pigs, opossums, turtles, squirrels, monkeys, lemurs, rats, skunks, possums, apes, baboons, badgers, and many species of rodents, birds, lizards, insects, and fish.

The Diversity of Feeding Strategies

Some groups of animals have obligate feeding strategies. This means that they must consume the kinds of foods their bodies were designed for. You will never see a carnivorous cow or a herbivorous lion. Some groups of animals, however, have been able to adapt their feeding strategies to their environment. This creates diversity among members of the group. Take bears for example. Even though all bears came from the same ancestors, you have herbivorous pandas in China, carnivorous polar bears in Canada, and omnivorous black bears in the United States. Pretty cool.

Diversity is a good thing in the natural world; the more of it, the better. With so many limiting factors in nature, it’s good to have a broad array of strategies to survive. Groups of animals that utilize a diversity of feeding strategies are usually successful. Take bats for example. There are different species of bats that are carnivores, herbivores, and omnivores. They have diversified not only to live in a wide range of different habitats, but to exploit a diversity of foods. This is one reason why they are the largest and most wide-spread groups of mammals.

The Big Picture

In the animal kingdom there are two basic types of organisms: plant eaters and animal eaters. Animals that eat plants are called herbivores while animals that eat other animals are known as carnivores. Carnivores (predators) tend to be quick, agile, and have strong, powerful bodies and weapons (like claws and teeth). Because herbivores consume plants (which are low in fat and protein) they have to spend more of their time foraging (searching for and eating food). This means that they need to eat regularly to keep their energy up. A carnivorous diet, on the other hand, is rich in fats and proteins so predators expend a high amount of energy at one time to catch their food, then spend most of their day resting. Some large predators may go several days without eating after a big meal. Whether you’re a carnivore or a herbivore, at the end of the day you need the right kind of nutrition to keep your body fueled and healthy. The types of feeding strategies that animals use are a product of their evolutionary history and the environment in which they live.

Feeding Strategy Quiz

Here is a fun activity to reinforce what you learned. Judging by the teeth of these animals, can you guess which ones are carnivores, herbivores, and omnivores?

An Amazing Student Video on Forestry Succession

A forest flourishes or perishes depending on environmental conditions.  As local conditions change, the types of plants that make up a forest also change.  The process is known as succession.  To visually describe forestry succession in forest in northern Wisconsin, a small group of students (Jaclyn, Jake and Ayla) from the Conservation School of Wisconsin produced this short piece.

http://blip.tv/play/hJw5gcr8QgA

The Stages of Forest Succession

The following diagram illustrates forestry succession

About the Conservation School

To learn more about this amazing school in the woods visit ConserveSchool.org

Everything you want to know about lake Succession!!

Freshwater lakes, in principal, are ephemeral. As a system they are created, they age, and they die, in a predictable pattern. This process of aging is what we call succession. Many palustrine systems like freshwater marshes and bogs are simply really old lakes and ponds. Lake succession is mainly driven by the input of organic matter and sediment into the lake system. As the lake fills up, it looses water and becomes a new type of system.

Watch a short overview Video from Untamed Science

http://blip.tv/play/hNNNgZmZMAA

Birth of a Lake

Lakes are born in many different ways. Receding glaciers can leave large depressions in the landscape which can quickly be filled with water and glacial out-wash. These types of lakes are called kettle lakes. Crater lakes are formed in the middle of a volcanic depression or the crater left by an asteroid collision. If the meandering pattern of a river pinches off it can leave an oxbow lake, a stagnant body of water in the depression of a former flowing river.

If you think you’ve noticed a pattern here you’re not crazy. Lakes are born in topographical depressions and filled with water. The speed at which the lake ages and goes through its stages of succession depends on the amount of water, nutrients and sediment being put in or taken out of it.

Filled in and Dried up: Bogs

Water loss and sediment fill are a main ingredient in lake succession. In the northern latitudes, kettle lakes dominate and sphagnum moss is the most common ground cover surrounding them. Sphagnum is wonderfully absorbent and is able to hold about one pound of water to every ounce of dry sphagnum. As the sphagnum grows around the edges of a lake, it quickly absorbs some of the water; this then creates more room for more moss to grow and so on until the entire ‘lake’ is covered in sphagnum. Over time, the layers of sphagnum moss decay to form peat layers. This lake can then be called a peat bog. Some bogs in the Denali National Park in Alaska can have over 20 ft of peat below the bog!

Bogs have very acidic soil and water. Because most decomposers cannot survive in such acidic soil, bogs can be rich with well preserved animal and plant remains. The acidic soils will also stunt the growth of trees and only allow for certain specially adapted plants to grow there. *The acidic nature of sphagnum moss makes it a great antiseptic and bandage in survival situations* Bogs are normally formed in higher altitudes where they are not fed by underground springs of water. If they are fed by underground springs then they are called fens. Because fens are not as dry as a bogs, they can remain in the late stages of succession for a very long time.

Eutrophication

A second way lakes can go through succession is through a process called eutrophication. This happens when nutrients are washed into the lake from the surrounding area, or watershed. Nutrients can include animal waste and fertilizers, which scientists call nitrates, and eroded inorganic material called phosphates.

Along with oxygen, nitrates and phosphates are requirements for life, especially plants. As more and more nutrients are washed into the lake, the more plants, like algae, are able to grow and reproduce. The more algae that grows, the cloudier, murkier and greener the water gets. Algae goes through photosynthesis like all plants, breathing in carbon dioxide and breathing out oxygen to form sugars. Initially, the amount of algae in the water increases the amount of oxygen available to other animals. Unfortunately, everything that lives has to die. When the algae dies it sinks to the bottom of the lake and decomposes. Along with sediment being washed into the lake from the surrounding area, the dead plant and animal material decomposes to from soil. The decomposers responsible for breaking down the dead organisms breathe oxygen. So, too much algae in the water can actually decrease the amount of oxygen, which can decrease the amount of living things that are able to live there.

This can get kind of confusing, all you have to do is remember the book If you give a mouse a cookie. Its a little silly, but just remember, every time you give the lake something its going to want something else. If you give a lake some nutrients, its probably going to want to grow some algae. If it grows some algae, it will probably want some oxygen to wash them down. Decomposition that happens deep in the soil without oxygen can smell really bad, like rotting eggs, because the bacteria that break it down use other gasses instead of oxygen to breathe. Just try digging your hand into some pond muck, YUM! Eutrophication happens slower in big lakes and lakes that don’t get many nutrients washed into them. Lakes that are in the beginning stages are called Oligotrophic, and lakes at the end stages are called Eutrophic.

Death of a Lake

The two processes that have been described here are not the only ways a lake can go through succession, and many times it is a combination of the two. A bog can go through eutrophication, and a eutrophic lake can become a bog. It all depends on the living (biotic) factors involved. The size of the lake can also effect how fast it ages. Lake Michigan is still oligotrophic despite being around for thousands of years. Eventually though, sediment from various sources will fill in a lake and most of the water will leave it, if there is not a source feeding it. When this happens the lake is essentially ‘dead’ and all that remains are traces of a once thriving ecosystem.