m3t03

=MODULE 3.3= =I. Topic Title:=

**__COMMUNITIES__**
=II. Topic Description:= = =

This topic deals with the basic definition of community ecology. It explains the different interactions that each population can do in order for them to survive. In line with that, the topic highlights some important adaptations and mechanisms for each organisms. It emphasizes also the role of predation and competition in a community.

=III. Terminal Objectives:=

The student should be able: 1. to define what communities are 2. to determine different interspecific interactions such as mutualism, commensalism, competition and predation

=IV. Content Presentation:=


 * __Introduction__**

Before starting with this section, review the biological hierarchy of life. The organism is the basic unit of ecology. Many organisms in a certain area pertain to a population. And many different types population that are INTERACTING pertain to a community. The word interaction is very important in the definition of a community. The need of this interaction can be positive, negative or neutral to both populations involved. This type of interaction is called interspecific. Interspecific interactions occur between populations of different species living together in a community. As stated earlier, this interaction may have different effects on the population density of organisms involved.

The types of interspecific interaction are mutualism, commensalism, predation and competition. Listed in Table 1 are the types of interactions and the effect of it to both species in terms of population density:

Table 1. Type of interaction and effect to the population density to both species
 * **INTERACTION** || **Species A** || **Species B** ||
 * //MUTUALISM// || + || + ||
 * //COMMENSALISM// || + || no effect ||
 * //PREDATION// || + || - ||
 * //COMPETITION// || - || - ||
 * //COMPETITION// || - || - ||

To further elaborate the table, interspecific interaction can have a positive, negative or neutral effect on the population density of one organism. If it is positive, it means their population is increasing. Negative, on the other hand, means it is decreasing while neutral indicates no change in the population size. Mutualism is an interaction where both species benefits while commensalism is an interaction where one species benefits while the other is unaffected. Predation, on the other hand, is an interaction where one species benefits while detrimental to the other. Lastly, competition is an interaction where it is dentrimental to both species.


 * __Predation__**
 * __Predation__**
 * __Predation__**

Predation is a type of interaction where one species benefits while its demtrimental to the other. In simpler words, one species gains while the other is actually harmed. The concept of predation is that a predator eats a prey. A perfect example of such animals that exhibits this type of interaction is a lion and zebra. But this old concept is now broadened. There are other kinds of predation namely: Parasitism and Herbivory.

Herbivory is considered as type of predation because herbivores like elephants and giraffes eat entirely the plant. On this effect, plant population decreases due to the rapid predation of herbivores. Since herbivores need plants for development, their population increases. Is parasitism considered a predation? To fully understand what parasitism is, access interactive learning 1 (IL1) entitled “Is parasitism a form of predation?”

Predation is an offensive move for capturing prey. With any offensive move, predators should possess characteristics so that they can capture prey efficiently. One example of animal that possess characteristics for prey capture are spiders. Spiders in the family Salticidae are ground-dwelling hunters. To capture prey, these spiders jump on their targeted prey with the aid of their two big frontal eyes and 4 smaller eyes that revolves around its head. Thus, the spider garners completely more than 180 degrees eyesight. This is an advantage for capturing prey in far distances. Access interactive learning 2 (IL2) entitled “Adaptations” to enhance your analysis on this matter.

Preys actually don’t want to be eaten as such. Evidently, predation is not always successful. Over repeated encounters with predators, the prey has developed defense mechanisms against the characteristics possessed by predators. For herbivory, plants have developed defense mechanisms such as thorns and secondary compounds against herbivores. Such examples of secondary that are palatable to us but not palatable to other organisms are opium, mint and cinnamon. There are many more of these secondary compounds that the plant manufactures within its body structure. Animals have developed also antipredator mechanisms in order to avoid being eaten. These defense mechanisms are either passive or active defenses. Such an example of passive defense is hiding while examples of active defenses are escaping and defending themselves. In table 2, it lists the different types of antipredator mechanism. Access interactive learning 3 (IL3) entitled “Examples of Antipredator Mechanisms”

Table2. List of antipredator mechanisms and its definition
 * **Mechanism** || **Definition** ||
 * 1.) Fleeing and Escaping || The most common antipredator response although it is energetically expensive. ||
 * 2.) Active Self-defense || Some animals would confront the predator and fight but it not common to animal groups. Other behavioral defense includes alarm calls, in which the prey turns the tables around (mobbing). ||
 * 3.) Camouflage || Also called cryptic coloration. It makes the potential prey difficult to spot against its background ||
 * 4.) Deceptive markings || It deceives predators momentarily, allowing the prey to escape ||
 * 5.) Chemical Defenses || These organisms are brightly colored, meaning a warning to predators (called aposematic coloration) ||
 * 6.) Mimicry || A phenomenon in which the mimic bears a superficial resemblance to another species ||
 * 7.) Defense Mutualism || It uses other animals in order to protect itself from predators ||
 * 7.) Defense Mutualism || It uses other animals in order to protect itself from predators ||



An example of Fleeing and Escaping by a Jesus Christ Lizard



A frog that is camouflaged in its surroundings

A moth with deceptive markings in its wings.

An example of defense mutualism of a boxer crab. The crab uses the polyps of the sea anemone for protection.


 * __Mutualism and Commensalism__**
 * __Mutualism and Commensalism__**

Mutualism and Commensalism are fairly the most popular community interaction. Its effects to the population density either increases or has no effect at all. There are several examples of this interaction among organisms. Research some examples of these types of community interaction.


 * __Competition__**

Competition is a type of interaction where it is detrimental to both species population. This interaction happens because both species rely on the same limiting resource such as food and water. Thus, the population growth of a species may be limited by the density of competing species as well as by the density of own population.

Access the handout of “Graphs on Competition”. There are three (3) graphs that are illustrated. This is actually a laboratory experiment done in order to confirm the definition of competition. The two species involved are //P. caudatum// and //P. aurelia//. In this experiment, these species were placed in a Petri dish containing available resources for growth and development. There growth was observed and recorded as time passes by. Each species were grown separately in a Petri dish and also they were also joined in one Petri dish. In graph A, it illustrates the population curve of //P.caudatum//. Now answer this, what is maximum number of individuals reached by //P.caudatum//? On what day did //P.caudatum// reached its highest number of individuals? Was there a decline in the curve? Also, employ this on graph B to //P.aurelia// with same set of questions. Now consider graph C where there is a mixed culture of //P. caudatum// and //P. aurelia//. Look at the population curve of both species in the mixed culture and compare that to the graphs employed earlier. What can you infer?

Obviously, the mixed culture is a type of competition interaction. Compare the population curve of P.aurelia of graph B and C. As observed on graph B, the maximum number of individuals reached until more than 80 on the 7th day. However in the mixed culture, the maximum number of individuals reached more than 80 on the 18th day. This indicates that P.aurelia was able to reproduce as fast as compared when it was alone in the Petri dish. This delay of reaching its maximum population growth is due to the presence of P.caudatum as a competitor in the Petri dish. Now, what can you infer to the population of P.caudatum? Compare graph A and C.


 * GRAPH A:** Population curve of //P.caudatum//


 * GRAPH B:** Population curve of //P.aurelia//




 * GRAPH C:** Mixed culture of //P.caudatum// and //P. aurelia//



= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =V. Activities:=

“Is Parasitism a form of Predation?”
 * INTERACTIVE LEARNING 1**

__Instructions__ For this 1st IL, research the definition of parasitism. And relate it on how it is considered as a form of predation. Prove your answer. Cite examples and discuss it briefly. Send your answer thru your instructor’s email address seen below the topic page.

Note: Please cite all references used for this activity.

“Adaptations” __Instructions__
 * INTERACTIVE LEARNING 2**

For the 2nd IL, research on different species of birds. Observe and describe the following features; head region, bill, legs, feet and wings. Take note on your entry their feeding habits and habitats. To specifically be successful on this IL, you need to answer these questions. Why do these birds have different structures? What is purpose of having this body structure against other possibilities? Rationalize your answer from the research data you gathered. Send your answer thru your instructor’s email address seen below the topic page. Note: Please cite all references used for this activity.

“Examples of Antipredator Mechanisms” __Instructions__
 * INTERACTIVE LEARNING 3**

For this 3rd IL, Table 2 already indicated the different types of antipredator mechanisms and its definition. Provide an example on each antipredator mechanism. Describe how they use this antipredator mechanism and clip a picture with it. Send your answer thru your instructor’s email address seen below the topic page.

Note: Please cite all references used for this activity.

=VI. References:=

Campbell N.A. and J.B. Reece. 2004. Biology 7th edition. Benjamin Cummings Stiling, P. 2001. Ecology: Theories and Applications 4th edition. Prentice Hall

=VII. Assessment:=

Enter here the link of the on-line test to help the learner evaluate his learnings of the topic.

=VIII. Disclaimer and Copyright Notice= Enter here the disclaimer and copyright text

=IX. Topic Writer:=

Thaddeus M. Carvajal tads.carvajal@gmail.com

Version 1.0 - Date:November 14, 2006 Revision 1.0 -Date:
 * X. Document History:**