Input Template for Content Writers
(e-Text and Learn More)
1. Details of Module and its Structure
Module Detail
Subject Name
Structure of Module / Syllabus of a module (Define Topic / Sub-topic of module )
< Species Interactions II>
2. Development Team
Role Name Affiliation
Subject Coordinator
Paper Coordinator
Content Writer/Author (CW)
Content Reviewer (CR) < Prof. NSR Krishnayya >
Language Editor (LE) < Prof. NSR Krishnayya >
Species Interaction II Ecology Negative interactions prevailing among different species
TABLE OF CONTENTS(for textual content)
1.Introduction: 2.Types of Negative Interactions: 2.1.Amensalism: 2.2. Predation 2.2.1 Predator-Prey Adaptations 2.2.1.1 Defensive Coloration 2.2.1.2Camouflage 2.2.1.3 Mimicry 2.2.2Predation- Prey Dynamics 2.3. Herbivory 2.4. Parasitism 2.4.1. Endoparasites 2.4.2. Ectoparasites 2.5. Competition 2.5.1 Different Types of Competition: 2.5.1.1 Intraspecific competition 2.5.1.2. Interspecific competition 2.5.1.3. Interference Competition 2.5.1.4. Exploitation competition 2.5.2. Models of competition 2.5.3 Competitive Exclusion Principle
1.Introduction: Ecological communities are assemblage of populations of different species, present in a defined geographic area. The species interact with each other directly and indirectly. The influence of interactions varies in degree of impact and outcome. Species interactions form the basis for many ecosystem properties and processes such as nutrient cycling and food webs. There are several classes of interactions which broadly are divided into positive and negative interactions.
2.Types of Negative Interactions: Negative interactions are mainly classified into following five types:
Interaction Effect on species A Effect on species B Nature of Interaction Amensalism (-) (0) One is harmed; other is unaffected Predation (+) (-) Beneficial to predator ; harmful to prey Herbivory (+) (-) Beneficial to herbivore ;harmful to plants Parasitism (+) (-) Beneficial to parasite ;harmful to host Competition (-) (-) Inhibitory to both Table 1: Types of Negative Interactions. The sign +, 0 & - represent the effect of one species on another and indicate positive, neutral or negative effect respectively.
Species Interaction II Ecology Negative interactions prevailing among different species
2.1.Amensalism: It is an antagonistic interspecificinteraction where one species suffers and the other species remains unaffected. This is commonly the effect when one species produces a chemical compound (as part of its normal metabolic reactions) that is harmful to the other species.It is also called antibiosis , the affected species is called amensal and the affecting species is called inhibitor. Allelopathy, in which some plants produce chemical compounds that inhibit the growth of nearby would-be competitors, is one type of amensalistic interaction ,for example Black Walnut tree (Juglans nigra), secretes juglone from its roots, it is a chemical that harms or kills some of the surrounding plants species(Fig.1). The other plants are prohibited from growing under or near the trees while the walnut trees do not really get benefit in any way. Interaction between an antibiotic and a pathogenic microbe is also an example of amensalism (antibiosis).
Fig.1 Black Walnut tree showing avoidance of plants in its close territory. (Source: www.biomiami.edu)
2.2. Predation: Predation is an in antagonistic interspecific interaction in which members of one species (the predator) consume members of other smaller species (the prey). In most examples of this relationship, the predator and prey are both animals; the best-known examples of predation involve carnivorous interactions, in which one animal consumes another .Predation is also exhibited by a group of plants. Carnivorous plants, such as the Venus fly trap, Bladderwort and Pitcher plant, consume insects. Pitcher plants catch their prey in a pool of water containing digestive enzymes, whereas the Venus fly trap captures an insect between the two lobes of a leaf and seals the insect inside with digestive enzymes (Fig.2 ).
A B Fig. 2 (A) Predator and Prey (Lynx and Hare) (B) A carnivorous plant (Venus fly trap) (Source: A - www.bio.georgeasouthern.edu; B - www.ehow.com)
2.2.1 Predator-Prey Adaptations:
Species Interaction II Ecology Negative interactions prevailing among different species
Predation has a direct effect on density of prey population .Both, prey as well as predator try to increase their efficiency ,prey tries to avoid predation and predator wants to catch maximum number of prey organism to satisfy its own hunger. During a long term history of predation both have developed number of adaptive features involving an evolutionary arms race.The major adaptive mechanism are :
2.2.1.1 Defensive Coloration: Many insects are brightly colored; they advertise their poisonous nature using an ecological strategy known as warning coloration, or aposematic coloration. It helps to prevent predation, by signaling to potential predators that the brightly colored individual is toxic. Toxins may be manufactured within the body or they may be acquired passively via consumption of toxic plants (Fig.3). Showy coloration is characteristic of animals that use poisons and stings to repel predators, while organisms that lack specific chemical defenses are seldom brightly colored.
A B Fig.3: Aposematic coloration shown by a caterpillar (A) and Dyeing Dart Frog (B) (Source: www.lifeandscience.org) 2.2.1.2Camouflage:One adaptation helping both predators and prey to avoid detection is camouflage; Camouflage consists of not only color but also shape and pattern. Camouflage, also called cryptic coloration, is a defense or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings.Cryptic coloration is especially common in small animals such as insects, lizards, snakes, and frogs. (Fig.4). In addition to visual crypsis there is also olfactory crypsis. This is the situation when an organism uses scent to camouflage itself. Camouflage is adapted by predators too.
A B Fig.4 Crab Spider(A) and Leaf butterfly (B) showing camouflage ( Source: www.duskyswodersites.com)
Species Interaction II Ecology Negative interactions prevailing among different species
2.2.1.3 Mimicry: In mimicry a species resembles to the superficial appearance of another species, it can be Batesian mimicryin whicha nontoxic species (the mimic) resembles a toxic species (the model) and is avoided by the predator in response to the toxic model species. Examples of such Batesian mimicry is shown by harmless Viceroy butterfly which mimics poisonous Monarch butterfly (Fig.5).The other type is Mullerian mimicry in which one toxic species resembles another toxic species and both are avoided by predator in confusion.
Fig. 5 Batesian mimicry exhibited by two species of Butterflies (Source: www.education.portal.com)
Evolution of surface features like thorns, spines hard shells etc. also protect prey from predation. Predators also follow some tactics to catch the prey like they show camouflage, release poisonous chemicals, form web or a trap etc.
2.2. Predation- Prey Dynamics: Predation is not as simple to understand as it seems. In complex food webs, a predator may also be the prey of another species. Some predators eat only specific types of prey, for example, the Canadian lynx feeds mostly on snowshoe hares during the winter. No other cat is so dependent on a single prey species, in this kind of close relationship, the sizes of each population tend to increase and decrease in linked patterns, and show a coupled oscillation. Initially, highprey density increases predator density to a point where the predation causes population decline in the prey, this decline affects dependent predator population and it falls ,this rise and fall is repeated in both populations (Fig. 6).Predator-prey dynamics are also influenced by climate dynamics, changes in food availability for the prey species, and dynamics in other areas of the food web.
Species Interaction II Ecology Negative interactions prevailing among different species
Fig.6 The predator-prey dynamics showing coupled oscillation in populations (Source:Hijausawah.blogspot.com)
2.3. Herbivory: Herbivory involves eating of plant material by an animal herbivore. Plants are eaten by a tremendous array of herbivores, it is a type of predation in which animals/organisms consume autotrophs such as plants, algae, and photosynthesizing bacteria.Itis almost always non-fatal, and can sometimes be advantageous for the plant, as it may stimulate growth and promote community diversity. Herbivores are at the second level of the food chain. Herbivores like squirrels eat grass and small plants near the ground and are called grazers, herbivores that eat leaves, shoots, and twigs are called browsers. Three terms are commonly used to describe the host range of herbivores, monophagous, oligophagous and polyphagous. Monophagous feeds on only one species of plant. Oligophagous feeds on several species of plants restricted to few genera or families while Polyphagous feeds on wide number of plant species .Like prey, plants also show many defensive mechanisms which can be physical or chemical. Herbivore-plant relationships also evolved into an “arms race”. Physical defense in plants includes evolution of thorns, spines, prickles, development of thick or waxy coating etc.(Fig.7). Chemical defense is done by producing secondary metabolites which may be bitter (alkaloids), poisonous (cyanogenic glycosides) or may make the plant unpalatable (polyphenols like lignin and tannin).
A B C
Fig.7 Defense features in plants : Thorns (A & B) waxy leaf (C) Waxy leaf (Source: A - www.smilinggardner.com; B -www.organostate.edu; C - www.forums.gardweb.com)
Species Interaction II Ecology Negative interactions prevailing among different species
2.4. Parasitism:It isthe relationship between two organisms in which one species (parasite) benefits for growth and reproduction to the harm of the other species (host). Parasites are divided into two categories: endoparasites, and ectoparasites
2.4.1. Endoparasites: Parasiteswhich live within the body of their hosts are endoparasites. Examples include flukes, tapeworms, fungi, bacteria, and protozoa.Fusarium sp (fungus), Erwinia sp. (bacteria), Meloidogynes sp. (plant parasitic nematode) are some of the endoparasitic organism that attack plants. All the 3 different parasites are feeding on the vascular bundles and the highly nutritious fluid that flow in the vascular bundle.
2.4.2. Ectoparasites: Parasites that feed on the exterior surface of an organism are ectoparasites. Examples include ticks and lice, plants, & protozoa. Many instances of external parasitism are known in plants.Rafflesia ,Orabanche, Cuscuta, Striga etc.are parasitic plants which depend on their host plants partially or completely (Fig. 8).
A B
Fig. 8 Plant parasites: Striga a root parasite (A), Cuscuta a total parasite (B) (Source: A - www.wageningenur.ne; B- www.wikepedia.org)
In most situations, parasites do not kill their hosts. An exception, however, occurs with parasitoids, which blur the line between parasitism and predation. The best-known parasitoids include several species of wasp, which immobilize , but do not kill a host by stinging it.
2.5. Competition: It is an interaction between species, in which the fitness of one is lowered by the presence of another. Limited supply of a common resource (such as food, water, and territory) leads into a struggle and reduces vigor of both the interactors. Competition is closely related with concept of niche, niche is the functional relationship of an organisms to its physical and biological environment. Niches are multidimensional in that they include a wide variety of aspects of the environment Whenever two niches overlap, competition starts between organisms. Competition is not always a straightforward, direct interaction either, and can occur in both a direct and indirect fashion. According to the competitive exclusion principle, species, less suited to compete for resources should either adapt or die out. According to evolutionary theory, the competition within and between species for resources, plays a critical role in natural selection. The outcome usually has negative effects on the weaker competitors.
2.5.1 Different Types of Competition: Depending on hierarchy of competitors competition can be intra or interspecific.
Species Interaction II Ecology Negative interactions prevailing among different species
2.5.1.1 Intraspecific competition: occurs when members of the same species fightfor the same resources in an ecosystem For example, two trees growing close together will compete for light above ground, and water and nutrients in the soil and this will affect growth of both of them, since member of the same species have the same niche and so compete for exactly the same resources. Intraspecific competition tends to have a stabilizing influence on population size. If the population gets too big, the competition increases, so the population falls again. If the population gets too small, level of competition decreases, so the population increases again .This is known as Law of thinning and constant biomass .
2.5.1.2. Interspecific competition: occurs when individuals of two different species share a limiting resource in the same area. If the resource cannot support both populations, then lowered fecundity, growth, or survival may result ,in at least one species. Interspecific competition has the potential to alter populations, communities and the evolution of interacting species.
Depending on mode of resource utilization competition can be of two types:
2.5.1.3. Interference Competition: When one individual directly changes the resource availability to other individuals, the interaction is known as interference competition.This generally happens when a resource is nondivisible, and leads to competitive exclusion where one competitor wins and excludes all others, from using the resource in that ecosystem or area. It is also known as contest competition. It is visibly shown by aggressive animals who do not allow their prey to be shared.
2.5.1.4. Exploitation competition: occurs when individuals interact indirectly as they compete for common resources, like territory, prey , food in animals and light, nutrients and space in plants. It is also known as scramble competition.
2.5.2. Models of competition: The impacts of interspecific competition on populations have been formalized in a mathematical model called the Competitive Lotka–Volterra equations, which gives a theoretical prediction of interactions. The model is based on the fact that when two species are interacting with each other the possibilities are ,they may compete for resources assist one another exclude one another kill one another
It combines the effects of each species on the other.
Where N1 and N2 are the population sizes of species 1 and 2, r1 and r2 are the intrinsic rates of increase for these species,
Species Interaction II Ecology Negative interactions prevailing among different species
K1 and K2 are the carrying capacities of the habitat for each species, α12is the harmful effect of one individual of N1 on N2
α21 is the harmful effect of one individual of N2 on N1
In these models, the rate of population growth of a species is reduced both, by conspecifics (individuals of the same species) and by individuals of the competing species, that is, interspecific competition .The terms α12 and α21 are called competition coefficients and express the competitive effects of the competing species on one another. The model predicts four possibilities 1. Species 1 wins and 2 goes extinct 2. Species 2 wins and 1goes extinct 3. Outcome depends on initial density of each species 4 .Both species coexist
Coexistence occurs when both species reach equilibrium densities i.e. population is not growing, the competition coefficients are less than 1 and interspecific competition is weaker than intraspecific competition. Coexistence occurs by niche partitioning , otherwise, one species is predicted to eventually exclude the other. These conclusions come from the following analysis. Populations of species 1 and 2 stop growing when: dN1 / dt = r1 N1 [(K1 –N1 – α12 N2) / K1] = 0 and dN2 / dt = r2 N2 [(K2 – N2 – α21 N1) / K2] = 0 That is, when: (K1 –N1 – α12 N2) = 0 and (K2 – N2 – α21 N1) = 0 Or, rearranging these equations, we predict that population growth for the two species will stop when: N1 = K1 – α12 N2 and N2 = K2 – α21 N1 These are equations for straight lines, called isoclines of zero population growth, where everywhere along the lines population growth is stopped: dN1 / dt = 0 and dN2 / dt = 0 Above an isocline of zero growth, the population of a species is decreasing; below it the population is increasing (Fig.9).
Species Interaction II Ecology Negative interactions prevailing among different species
Fig.9 The orientation of isoclines for zero population growth and the outcome of competition according to the Lotka- Volterra competition model. (Source: www.skysenu.edu.com)
2.5.3 Competitive Exclusion Principle: It was proposed by Russian biologist G.F.Gause (1934). It states that two species whose niches overlap too much by requiring the same resources cannot coexist indefinitely in the same ecosystem. One of the species will always be at least a little better than the other, and eventually eliminate the inferior species in that area. This process is called the competitive exclusion. In case the two have to survive or co-exist there should be ecological difference between them. In such situation the two organism unit can never be similar and there has to be some difference between the two. This experiment was carried out by using two species of Paramecium (P. aureliaand P.caudatum) which were first grown in separate cultures and each exhibited typical normal sigmoid growth in controlled culture with constant food supply. However, when both species were grown together in the same culture, both of them competed for the limited food available. Because P. Aurelia could gather food more quickly, P. aureliasurvived and reproduced, while P. caudatum starved. Eventually only P. aurelia remained in the culture (Fig.10).
Species Interaction II Ecology Negative interactions prevailing among different species
Fig.10 Growth curves of two Paramecium species demonstrating the principle of competitive exclusion. (Source: www.biology.net23.net) The concept of competitive exclusion is now firmly established and many ecologists believe that two species cannot exist on the same limiting resource indefinitely, ultimately even a slight reproductive advantage to one of them will result in the displacement of the other. In terms of the niche-if the niches of two species overlap completely, only the superior competitor can survive. However it remains a fact that consequence of competition can be competitive exclusion or coexistence.
3.Summary There are many different kinds of interactions between organisms in an ecosystem and it is not unusual for any particular organism to play multiple roles at different times. The interactions are of various categories positive, negative or neutral .The first two interactions play important role in functioning and structuring of community. Negative interactions include amensalism ,predation,herbivory, parasitism and competition. Amensalism is one sided interaction while in predation, herbivory and parasitism one interactor is benefitted and other is harmed . In competition both the species are negatively affected .Each of these interactions has its own significance and has exhibited important consequences in long term.Evolution of adaptive features in animals and plants are responses to specific type of interaction .Coexistence and/or competitive exclusion are two very significant outcomes of competition which decide whether the species will live together or some of them will be eliminated .Thus these two phenomena highly influence the type of associations found in a community.
References: 1. Agrawal A. A., Ackerly D. D., Adler F., Arnold A. E., C., Cáceres D.F., Doak, E., Post, P. J. Hudson, Maron J., K. Mooney A., Power M., Schemske D., Stachowicz J., Strauss S., Turner M. G., and Werner E. (2007). Filling key gaps in population and community ecology. Frontiers in Ecology and the Environment5: 145–152. 2. Begon, M., J. L. Harper, and C. R. Townsend.(1996). Ecology: Individuals, Populations, and communities, 3rd edition. Blackwell Science Ltd. Cambridge, MA. 3. Cornell, H.V. & Lawton, J.H. (1992). Species interactions, local and regional processes, and limits to the richness of ecological communities: a theoretical perspective. Journal of Animal Ecology, 61, 1–12. 4. Gotelli, N. J. (1998). A Primer of Ecology, 2nd edition. Sinauer Associates, Inc. Sunderland, MA. 5. Moon, D.C., Moon, J. and Keagy, A. (2010). Direct and Indirect Interactions. Nature Education Knowledge 3 (10): 50.
Species Interaction II Ecology Negative interactions prevailing among different species
6. Ricklefs.R.E. & Miller L.G. (2000). 4th Edition (Eds.) Ecology ,Freeman &Co.USA (NY) 7. Smith, R.L., & T.M. Smith. 2001. Ecology and Field Biology,6th ed..Benjamin Cummings
Species Interaction II Ecology Negative interactions prevailing among different species