1    

Lab 14 Ecology WARNING: This lab may take place outside with a good bit of running around, so dress appropriately.

INTRODUCTION TO ECOLOGY Sometimes, nature is a hard place to live. Most organisms probably worry about fewer inconveniences than your average American, but those worries are pretty severe: how can I get enough food to survive and reproduce without getting eaten? How can I find water and avoid freezing? Organisms face these dilemmas all the time; it is how they interact with their environments. Ecology is the study of how organisms interact with each other and their environments. This can be measured on many levels: Level Definition Example

Individual

A single organism of a species   A grey squirrel spends 30% of its time foraging, 10% of its time building shelter, 40% of its time watching for predators, and 20% of its time sleeping.

Population A group of interbreeding individuals of the same species living in the same area

If the grey squirrels in this forest don’t produce 5 babies/pair/year, the population will decline.

Species

All populations that whose members (1) share similar anatomical (definitive) characteristics (morphological species concept) and (2) have the ability to interbreed with each other, but not with other groups (biological species concept)

Grey squirrels (Sciurus carolinensis) live in the eastern part of North America from Florida to Canada, from the east coast to Texas.

Community Different species living in a given area and interacting either directly or indirectly.

Grey squirrels compete with chipmunks for the seeds from many types of trees such as oaks, walnut, and pecan.

Ecosystem Species or communities interacting with their environment. All the interacting parts of the physical (pH, temperature, salinity, etc.) and biological worlds.

Grey squirrels cache seeds by burying them and build nests of leaves to survive the subfreezing temperatures of northern winters.

All living things have to meet certain needs in order to survive, grow, and reproduce. There are also factors they must avoid in order to survive, grow, and reproduce. These requirements are often broken down into two types: conditions and resources. Taken together, these requirements determine much of a given species’ distribution: where organisms are found, and abundance: how many individuals are found there. For example, the picture shows the natural distribution of hedgehogs. CONDITIONS AND RESOURCES • Conditions (physical factors) are physical and chemical features of the environment, such as temperature,

humidity (terrestrial), osmotic pressure or pH (aquatic), that determines where an organism lives. Conditions can be altered by an organism in its immediate surroundings (sometimes a larger area), but are never consumed by the organism. Conditions are relative to the organism under study. Most organisms are relatively intolerable of conditions outside of a small range, but that range can vary greatly among different life forms. For instance, humans are usually whining if their immediate temperature rises above 24°C and humidity of more than 60%. Whereas some members of the domain Archaea can live in temperatures of 122°C and stop growing or die at temps lower than 80°C. We call these “extremophiles,” because to us, they love extreme conditions. But to them, our “room temperature” is deadly.

• Resources are all things needed by an organism that are consumed by the organism for growth and development or other activities. Consumed does not mean eaten, but used to the exclusion of other organisms. Food, shelter, light, living space, nitrogen, and mates are common examples.

2    

Most organisms are adapted for 3 things relevant to resources and conditions: 1) Finding food. For example, sharks have eyes, nostrils, and ampullae of

Lorinzini (special sensing organs called electroreceptors) to find prey fish. Plants dig deep into the soil with their roots for nutrients, and use their solar-panel leaves to make their own food from inorganic molecules.

2) Finding a mate. For example, the large antennae of this male moth help him follow the pheromones of females in the dark. Flowers are adaptations to attract pollinators that carry pollen between individuals.

3) Avoiding getting killed. This last condition takes energy and resources away from 1 and 2, but it is important. Cacti and the extinct ankylosaurus are well armored to ward of potential predators. The thick fur of the arctic fox and needles on conifers are adaptations to avoid freezing to death.

3    

CARRYING CAPACITY When resources are plentiful, individuals in a population can find enough food to survive and reproduce easily and the population will grow. In this case, the number of births > the number of deaths. More often, resources are limited; each environment can only support a certain amount of resource users. Populations will grow until resources are used up and become scarce. Then, growth slows to a point that is sustained by the amount of resources. Each environment can only support a certain number of individuals of a given species. At this point, the number of births = the number of deaths, the population’s size will remain constant, and the population will be in equilibrium (the horizontal part of the lines below). The number of individuals that an environment can support is its carrying capacity. Of course, carrying capacity varies depending on the species and the amount and type of resource each individual uses.

When resources are less plentiful, like during a drought, the carrying capacity will be smaller. The population may still reach an equilibrium, but at a smaller overall population size. If resources become even scarcer, the number of births might be < the number of deaths, and the population will decrease.

Other forces can also affect population size and growth rate. Abiotic factors, such as temperature, can cause population growth rate to expand suddenly, as when temperature goes up in the summer causing plants to seed, or crash suddenly as when resources become scarce due to winter weather. The up and down pattern to the number of female sparrows to the right is an example of a population that grows and crashes every 10 years. The full set of conditions and resources determines a species’ ability to survive, grow, and reproduce in an area. Sometimes, an organism can live in a place, but there are not appropriate conditions and resources to allow it to grow and reproduce. Sometimes even low levels of a certain condition are enough to prevent survival, such as with toxins. Sometimes only a low level is necessary and too much is harmful, such as with some essential nutrients or water. All three must be appropriate to maintain a healthy population.

4    

INTERACTIONS No organism stands alone. They all require a certain amount of resources to survive, grow, and eventually reproduce. Resources are, of course, generally limited. Often two or more organisms will want the same resources. If so, they will compete with each other for those resources. Sometimes, another individual is their resource, so they have to kill for it. These relationships are called interactions. Organisms will lie, cheat, and steal from each other. On a more positive side, organisms can also work together for resources or to mediate harsh conditions. Competition Since resources are usually limited and individuals might need the same resources, they may have to struggle with each other for access to those resources, this causes competition. Competition is what happens when two or more organisms need and seek the same resource. Remember that resources are used by the organisms. That means that when one organism uses a resource, another organism cannot use it. This leads to competition. Competition greatly affects population dynamics. Organisms compete for all kinds of resources, including mates, food, space, shelter from predators, light, nitrogen, carbon, and many others. Since the organisms would rather there be no competition and take all the resources for themselves, competition is negative for both parties.

By definition individuals of the same species are similar in morphology and live in the same habitat, therefore they are very likely to need the same resources. Therefore, intraspecific competition (competition within a species) is common. Individuals in the same population (and therefore the same species) often compete for space and food. The two beetles shown at left are wrestling for a chance to mate with a nearby female.

In other cases, members of one species require the same resource as members of another species with which they co-occur. When this happens, the two species are in interspecific competition with one another. The trees pictured at right grow tall as they are competing for access to light.

Changes in the population size of species A can affect the rate of population growth of species B and vice-versa. In these situations, both species are usually found in numbers below that (carrying capacity) which they would achieve if they occurred alone. Sometimes both species will continue to exist indefinitely at these reduced population levels in a stable competitive equilibrium (graph at bottom left). At other times one species will eventually drive the other species to be extirpated (removed from the area where the competition exists) in a process termed competitive exclusion (graph at bottom right).

5    

INTERSPECIFIC INTERACTIONS The first organisms to evolve were probably autotrophs since there was no other organic matter around to eat. Autotrophs (producers) are organisms that get their organic matter and energy from an abiotic (nonliving) source. Bacteria and plants, the most common autotrophs today, do this through the process of photosynthesis in which they take carbon dioxide, water, and energy from sunlight and convert it into glucose, an energy-storage and body-building molecule. It wasn’t too long though, before some other creatures evolved to steal these molecules from the autotrophs by eating them. Heterotrophs (consumers) are organisms that get their energy and matter from an organic (living or formerly living) source. We can think of three main ways to be a heterotroph:

1. Predation 2. Parasitism 3. Saprophagy (decomposition)

Get energy and matter from a living source by killing it

Get energy and matter from a living source without killing it. More than half of all species on Earth are parasites.

Get energy and matter from a formerly-living

source

Ants killing and eating a

katydid.

Deer eating leaves. Mistletoe on a tree.

Nematode on intestinal wall.

Fungi feeding on dead

wood.

Together, these organisms cycle nutrients and matters through each other and the environment, thus forming an ecosystem.

This is a drawing of the protist Tetrahymena (a heterotroph) trying to eat some cyanobacteria (autotrophs).

6    

Predator-Prey interactions Predation is a major selective and ecological force for most organisms. In the above scenarios, organisms are free to forage at will as long as resources are available. However, predation, in which one organism kills and eats another, can also affect foraging and population size and growth. Predators can keep population sizes of their prey low directly by eating individuals. They can also affect resource use indirectly. When predators are in the environment, foragers must often choose between foraging for resources and keeping a watch out for

predators. This limits the rate of resource depletion in an area. Predators can also mediate competitive exclusion. If predators eat the most common prey species, no matter what species it is, then none of the prey species can reach maximum population size, reducing the ability of the better competitor to wipe out the worse competitor. Rather than reaching an equilibrium in which individuals of a population survive and reproduce in proportion to the carrying capacity, some populations undergo boom-and-bust cycles. In this case, the population grows rapidly during a period called a boom. As the population grows, resources will become relatively fewer, the individuals will become more crowded and reproduce

less, and the population will begin to fall dramatically, or bust, as individuals can no longer support or replace themselves. Sometimes, boom-and-bust cycles also involve predators. When the prey species is numerous, the predator populations can begin to boom. When the predators become plentiful, they will start to drive the prey species into a bust. When the prey species is very scarce, predator numbers will start to decline, causing them to bust. When there are fewer predators, the prey species will start to boom again, causing the cycle to continue. A well-known example of a boom-and-bust cycle that involves both a predator and a prey organism are the snowshoe hares and their predator the lynx.

Apparently though, this type of cycling is rare because predators often only feed on the sick, injured, and old, so only take out those that were dying anyway. Predators can also shift to other prey as their prey of choice becomes scarce, lowering the effect on any given prey species. Nonetheless, organisms that face predation have evolved many defenses to prevent it, such as camouflage, spines, shells, speed, scare tactics, toxins, and more. So it seems that predation is still a major selective force.

And predators new to an area have been known to cause their prey to go extinct there.

7    

Mutualisms Not all relationships among species are filled with danger and thievery of resources. Sometimes two species actually work together to obtain resources. A mutualism occurs when two species are in a relationship in which both benefit. Usually this means that they help each other obtain resources that they otherwise would not be as efficient at getting. Mutualisms increase the population growth of both species. Although we will not see mutualisms in today’s lab, I wanted to add the brighter side of ecological relationships. Mutualisms help organisms get food, fight off competitors, predators, and parasites, and even survive –30°C winters. Pretty much every species you can think of depends on another in some way. For instance, without the bacteria in your guts, you would not be able to digest your food causing you to starve to death. Here are some very common and critical mutualisms: • Fungi and plants. All gymnosperms and 80% of angiosperms depend on mycorrhizae, a

small fungus that surrounds the roots of these plants, in order to absorb enough nutrients to grow tall. The fungus receives carbohydrates from the plant for its efforts.

• Cellulose eaters in animal guts. As a rule, animals cannot digest cellulose, the main structural component of plant cells. After eating a plant, the animal chews it to bits, then sends it down to the bacteria in their guts to break the cellulose apart further. Cows (and other herbivores) have a multiple-chambered stomach to serve as fermentation chambers for their gut microflora. The bacteria get a home and steady food source.

• Angiosperms and pollinators. Plants can’t move and so getting their gametes to another individual is tricky. To facilitate this, they evolved flowers and nectars to attract an animal (which can move) to carry their pollen for them. In return, the pollinator gets a sweet reward.  

Here is an amazing mutualism:

8    

OUTDOOR LAB ACTIVITY Be Prepared: This activity will be conducted outside and there may be some running around. WEAR APPROPRIATE ATTIRE FOR THE WEATHER AND IN CASE YOU GET DIRTY! We will be collecting data in a grassy area on campus. This is a foraging game. It will give you a chance to feel what it is like to be a lonely forager having to compete with other foragers and survive predators. There are 5 rounds that will consist of 30-second bouts. The instructor will control the timing of the rounds. Depending on the size of the class, the instructor will take notes or a volunteer student can, but you will need to get the data at the end of class for your own analyses. We also need help setting up the food items. Consider yourself a bird. Imagine that you are a robin collecting worms in the summer. You are hungry for worms. Various worms will be distributed throughout the main lawn. These are your food items (unless you are a predator, see round 5). Rounds are composed of bouts of foraging. Bouts take 30 seconds or until all the food items are gone. To begin each round, a certain number of foragers will be released into the foraging area to forage. Each forager must collect 3 food items in order to survive and 5 food items to reproduce. You need to collect a certain number of worms in order to provide your young with enough nutrients to grow up and to provide yourself with enough energy and nutrients to feed them. If you are a forager and do not collect 3 food items, sorry you didn’t make it, you cannot participate in the next bout. If you collect 3 food items, you can participate as before. If you collect 5 or more food items, then you AND an additional forager of your choosing will forage in the next bout. The food items must be redistributed THOROUGHLY between each bout. Bouts will continue as long as deemed necessary by the instructor. Then we will start the next round under different conditions. These are the specific conditions for each round. The numbers may vary depending on the number of people in the lab section. Round 1 50 food items 4 foragers Round 2: fewer resources 25 food items total 4 foragers Round 3: a better competitor 25 food items of 2 types: green and white 2 foragers that can use all resources, 2 foragers that can use only 1 type of resource Round 4: specialization 25 food items of each type 4 foragers of each type, both are specialized

Round 5: predator 50 food items of one type (or no specialization) 4 foragers 1 predator comes out at 4 seconds (or count to 4). Predator attacks by tagging someone. Then they must walk them out of the arena, before moving on (this equals your handling time). Predators need 1 forager to survive and 2 to reproduce.

9    

Lab 14: Ecology Postlab OUTDOOR ACTIVITY. Name _______________________ 1. Number of players. Not all rounds will go 15 bouts.

Bouts Round 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 Foragers

2 Foragers

3 Better competitor

Worse competitor

4 A

B

5 Foragers

Predators

Complete the following for each round.

A. Chart your results for each round using lines. Remember, if there are 2 kinds of foragers, or foragers and predators, your graph must have more than 1 line.

B. Label the lines or provide a key. C. For each round, explain what happened in terms of resources, population size, population growth,

foraging, competition, predation, and carrying capacity.

2. Round 1:

10    

3. Round 2

4. Round 3

11    

5. Round 4

6. Round 5

4. Describe another mutualism not mentioned in this lab. Make sure to include the two participating species

and the benefits each receives.