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S. S. College, Jehanabad Department: Zoology Class: M.Sc S. S. College, Jehanabad Department: Zoology Class: M.Sc. Semester II Subject: Zoology Topic: Biological interaction in ecology Mode of teaching: Google classroom & WhatsApp Date & Time: 09.09.2020 & 10:30 Teacher: Praveen Deepak To join Department’s group, students can use following link https://chat.whatsapp.com/EHuHNfQzoAzJBMFNJvsjQx or scan QR Code WhatsApp No.: +91 75360 68068 BIOLOGICAL INTERACTION IN ECOLOGY ____________________________________________________________ Biological interactions , also termed as species interaction , are the interactions between organisms in an ecological community, which is defined as an assemblage of populations of at least two different species that interact directly and indirectly within a defined geographic area. In a natural habitat, no organism exists in absolute isolation or alone, and thus every organism interacts with the environment and other organisms. It is said that this interaction between the organisms and its environment is the fundamental to the survival of that organism as well as balanced functioning of an ecosystem. Thus, s pecies interactions form the basis for many ecosystem properties and processes such as nutrient cycling and food webs. Therefore, species interactions in the ecology are the relationships between two species each other in an ecosystem, which can be either of intraspecific interactions or interspecific interactions. Intraspecific interactions are those that occur between individuals of the same species, while interactions that occur between two or more species are called interspecific interactions . However, since most species occur within ecological communities, these interactions can be affected by, and indirectly influence, other species and their interactions. The most studied species interactions include competition, predation, herbivory and symbiosis . However, many more other types of species interactions also exist in nature. The interactions between the species are meant to facilitate the movement of energy from one trophic level to another. However, the nature of these interactions greatly depends on the environmental conditions in which they occur and are linked to their evolutionary context. Depending upon the nature of effect of interactions, various categories of the effects of a change in abundance, or presence vs. absence of one species on another have been carried out, which are as follows; − Direct effects refer to the impact of the presence (or change in abundance) of species A on species B in a two-species interaction. − Indirect effects refer to the impact of the presence (or change in abundance) of species A on species C via an intermediary species (A → B → C). − Cascading effects are those which extend across three or more trophic levels, and can be top-down (predator → herbivore → plant) or bottom-up (plant → herbivore → predator). − Keystone species are those which produce strong indirect effects. Keynote species: In nature there are big players and little players. The biggest players of all are referred to as keystone species. This is a species whose presence or absence, or substantial increase or decrease in abundance, profoundly affects other species in the community. Evidence usually comes from experiments in which one species is added to or removed from a community. The name derives from the center stone in an arch supporting its weight by inward- leaning stones. Removal of the keystone causes the balancing arch to collapse. The example can be derived from the rocky inter-tidal zone of Washington state where starfishes have been shown to be a keystone species. The entire community lives on relatively vertical rock faces in the wave-swept inter-tidal zone in which the community of marine invertebrates and algae are adapted to cling or adhere to the rock face. These marine invertebrates, which is a bivalve mussel Mytilus (competitive dominant), fed upon the zooplankton coming through the Praveen Deepak, Department of Zoology, S. S. Colleg e, Jehanabad tides and these mussels are fed upon by a starfish Picaster (predator) making space available for other species, and consequently is critical to maintaining a diverse biological community. The interactions between the organisms are classified differently on different basis, such as classification of interactions on the basis of effect and classification of interactions on the basis of mechanism. Types of interaction of organisms on the basis of effect These types of classification of interactions among the organisms are based on the quality of benefit or harm in terms of fitness experienced by participants in an interaction. There are six possible combinations, ranging from mutually beneficial through neutral to mutually harmful interactions. The level of benefit or harm is continuous and not discrete, such that an interaction may be trivially harmful to deadly. It is important to note that these interactions are not always static. In many cases, two species interacts differently under different conditions. These interactions can be understood as follows; Neutralism It is the most common type of interaction in which neither population affects the other. In other words, it is the relationship between two species which interact but do not affect each other. It describes interactions where the fitness of one species has absolutely no effect whatsoever on that of the other. True neutralism is extremely unlikely or even impossible to prove. When dealing with the complex networks of interactions presented by ecosystems, one cannot say positively that there is absolutely no competition between the organisms or no benefit to either organism. Since true neutralism is rare or nonexistent, its usage is often extended to situations where interactions are merely insignificant or negligible. Example can be given by the existence of tarantula and cacti in dessert. Amensalism It is the relationship between two species in which one impedes or restricts the success of the other while the other species has no effect on it. It is a type of symbiosis. Usually this occurs when one organism exudes a chemical compound as part of its normal metabolism that is detrimental to another organism. Example of this relationship is given by bread mold Penicillium , which secretes penicillin, a chemical that kills bacteria. A second example is the black walnut tree ( Juglans nigra ), which secrete juglone , a chemical that harms or kills some species of neighboring plants, from its roots. This interaction may still increase the fitness of the non-harmed organism though, by removing competition and allowing it access to greater scarce resources. In this sense the impeding organism can be said to be negatively affected by the other's very existence, making it a +/- interaction. A third simple example is when sheep or cattle make trails in grass that they trample on, and without realizing, they are killing the grass. It is the contrast of commensalism and goes in line with antibiosis or allelopathy. 2 | P a g e Competitions It is generally based on common resource that is in limited supply, in which two organisms vie or compete eagerly each other in order to do or achieve something. More generally, it can be defined as the direct or indirect interaction of organisms that leads to a change in fitness when the organisms share the same resource. The outcome usually has negative effects on the weaker competitors. Therefore, competition is a mutually detrimental interaction between individuals, populations or species, but rarely between clades 1. In extreme cases, such as in synnecrosis , interaction is so mutually detrimental that it results in death, as in the case of some parasitic relationship. Synnecrosis is a rare and necessarily short lived condition as evolution against it. There are three major forms of competition, namely interference competition, exploitation completion, and apparent competition. Two of them, interference competition and exploitative competition , are categorized as real competition, while third form, apparent competition , is not considered as real competition. Interference competition occurs directly between individuals, while exploitation competition and apparent competition occur indirectly between individuals. These competitive interactions between the organisms can be outlined as follows; Interference competition: This type of competition between organisms involves direct interaction by fighting for scarce resources. This applies to both intraspecific and interspecific competition. In intraspecific competition , the competing organisms are of the same species, such as large aphids defend feeding sites on cottonwood leaves by kicking and shoving smaller aphids from better sites, and male deer lock horns when competing with other individual of the same species. All these competing organisms of same species vie for same resources such as territory, mater, food, etc. In interspecific competition , the opposing organisms are of different species, such as the rivalry between a lion and a tiger competing for the same prey. Exploitative competition: This type of interaction between organisms involves indirect interaction but in spite of that resulting in the depletion of the amount of resources thereby limiting the availability of these resources for other organisms. Similar to interference competition, the exploitation competition applies to both intraspecific and interspecific competition. In intraspecific competition , the competing organisms are of the same species. They vie for same
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