1.2. Inter and Intra specific relationships between organisms

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1.2. Inter and Intra specific relationships between organisms Activity 1.2 Observe the figure below showing interactions between organisms and answer questions below: Figure 1.2: Inter and intraspecific relationships between organisms a) Mention different biological interaction (inter and intraspecific relationships) labeled by letter A, B, C, D, E, F, and G b) For each provided interaction, give its meaning and your own example in each case. c) Explain the significance of each organism’s interactions in nature. Under natural conditions, plants and animals interact with other organisms of the same species as well as those of different species. The various organisms that surround and interact with a particular organism constitute its biotic environment. Such interactions have a great influence on the distribution and abundance of any one given species. Some of the most important interactions are: competition, parasitism, predation, saprophytism, mutualism and commensalism. 1.2.1. Competition (–,–) In both types of competitions, the two or more species competing for the same resource inhibit one another directly or indirectly. That is why they are denoted as (–, –) signs. a) Intraspecific Competition Intraspecific competition is a competition where individuals of the same species compete for the same limited resources in an ecosystem. The resources could be food, water, space, light, mates or any other resource which is required for survival. Significance of Intraspecific Competition Intraspecific competition acts as an important regulator of population size, meaning successful individuals will survive while unsuccessful individuals will die. It can also be called population density dependent regulator. Moreover, since intraspecific competition results individuals with different reproductive success, it can be a selective factor in evolution. b) Interspecific Competition Interspecific competition is a type of competition in which individuals of different species compete for the same limited resources in an ecosystem. The resources could be food, space, light, water, etc. In this kind of interaction, populations of the two or more species are affected adversely. Significance of Interspecific Competition Gause’s exclusive principle states that the species with identical ecological requirements cannot coexist over a long period of time. The less-fit species in the competition will be replaced by the better-fit species. Thus, in such situations, where interspecific competition is intense, the competition acts as one of the most important factors in structuring ecological communities and also as an agent of natural selection. Competition can cause species to evolve differences in traits. The characteristics that enable an organism to reduce competition will function to improve fitness; therefore, influencing the evolution of characteristics related to the acquisition of resources. Difference between Intraspecific and Interspecific Competition Intraspecific competition Interspecific Competition ȃȃIt is a competition among the individuals of the same species. ȃȃThe competition is among the members of different species. ȃȃThe competition is for all the requirements. ȃȃThe competition is for one or a few requirements. ȃȃThe competing individuals have similar type of adaptation. ȃȃThe competing individuals have different types of adaptations. ȃȃIt is more severe due to similar needs and adaptations. ȃȃIt is less severe as the similar needs are a few and the adaptations are different. ȃȃExample includes finding mating partners. ȃȃExample includes competition for food. 1.2.2. Parasitism (+, –) Parasitism is an association between two different organisms, in which, one called the parasite obtains food and sometimes shelter from the other which is called the host. The host does not gain from the association and is usually harmed. Parasites are only found where there are suitable hosts. Parasites can be a number of things, including plants, animals, and even viruses and bacteria. For example, the malaria parasite, Plasmodium vivax, is only found in tropical and subtropical regions where its intermediate host, the female Anopheles mosquito inhabits. Types of parasites Parasites are classified by how they interact with their host. Overall, parasites are much smaller than their hosts and reproduce at a faster rate. a) Ectoparasites The term “ecto” in Greek means outside. Therefore, parasites that live on their host are termed ectoparasites. Examples of ectoparasites are fleas, ticks, and mites (See Figure 1.3). These parasites live on larger animals, like cats, dogs and deer. Image 1 Safari Bio ECLPE Figure 1.3: Ectoparasitism (A flea on a dog’s skin) b) Endoparasites Similarly, the term “endo” in Greek means inside. Parasites that live inside their host are termed endoparasites. These include the things like parasitic worms, bacteria, and viruses. Tapeworms are endoparasites. They live in human intestines where they feed on the partially-digested food in their host’s intestines. It is a fully protected environment and they grow and thrive in these conditions. The tapeworms have no digestive system of their own, but absorb nutrients through their skin from partially digested food as they pass through the host (See Figure 1.4). Figure 1.4: Tapeworm Significance of Parasitism 1. Parasitism alters the behaviour and morphology of their hosts. This alteration increases the chance of being preyed by the predators thereby assisting the parasites to move from one host to another to complete their life cycle. 2. Parasitism promotes coexistence in biodiversity. Usually in an ecosystem, a competitively dominant species out-competes a competitively inferior species and doesn’t allow coexistence with this species. However, parasites reduce the competitive ability of the dominant species in a biodiversity and, thereby, allow a competitively inferior species to exist together with a dominant species. 3. Parasitism affects the keystone species and modifies the structure of ecosystem. In an ecological community, the effect of parasitism is the strongest when the hosts are keystone or dominant species with crucial functions in an ecosystem. 4. Parasitism leaves parasite with no responsibility. A social parasite is a parasite that takes advantage of the interaction of other organisms. The best example of a social parasitism is brood parasitism. This is an interaction where the parasite, typically a bird, deposits its eggs in the nest of another species. The host (another species) then ‘babysits’ the egg in place of the parasite (bird), allowing the parasite to deposit eggs in other nests instead of spending time hatching their own young. Adaptations of the parasites include: a) Being smaller than their hosts. b) Reproducing relatively faster. c) Having penetrating and attachment organs. d) Surviving in areas with low oxygen concentration. 1.2.3. Predation Predation is an interaction between the two species, i.e., predator and prey, in which one species (predator) uses another species as food (prey). In other words, one organism kills and consumes another. Predation influences the distribution, abundance and diversity of species in ecological communities. Types of Predation Generally, predation can be divided into: a) Carnivory Carnivory takes place when a predator consumes meat, rather than plants, and consequently kills its prey. Organisms that prefer meat to plants are accordingly called carnivores. The example of the lion hunting the buffaloes is called carnivory (See Figure 1.5). In this type of predation, a predator kills its prey more or less immediately. Other examples are a shark eating a tuna or a Venus fly trap consuming a fly. Figure 1.5: Lion attacking the prey b) Herbivory Herbivory is the act of animals eating plants. Or when an animal uses a plant as food, it is called herbivory. Example, when a deer eats grass, the plant is the prey and the animal the predator (See Figure 1.6). Figure 1.6: Herbivory: Deer eating grass Predation and Adaptation Adaptation in Predator Species Based on their experience, predators also undergo certain adaptations to be an efficient hunter or killer. These adapted traits are passed down from generation to generation. Predators exhibit traits such as sharp teeth, claws, and venom that enhance their ability to catch food (See Figure 1.7). They also possess extremely acute sensory organs that help them to find potential prey. Depending upon the requirement that arises, predators also adapt themselves to become much more efficient. Examples of some adapted animals are: a) The ability of raptors to spot potential prey from over a kilometre away. b) The acute sense of smell of moles. c) The ability of owls to locate mice by sound. d) The ability of pit vipers to sense body heat while tracking prey. e) The ability of bats and dolphins to echolocate. Predators catch their prey either by pursuing potential prey or by ambushing them. Organisms that give chase are capable of short bursts of speed like Cheetah (Figure 1.8). Those that lie in wait tend to be camouflaged to avoid detection. Figure 1.7: Adapted sharp teeth (canine) Figure 1.8: Cheetah adapted to run fast to of lion capture prey Adaptation in Prey Species In the same way, as much as predator adapts itself to capture prey, preys also adapt as much as possible to escape from the predators. Many, such as leaf insects, moths, a variety of frogs and small lizards, and herbivorous mammals, are cryptically coloured to make them more difficult to see. Other preys resemble inedible inanimate objects or unpalatable organisms. This is called mimicry. For example, walking stick insects resemble dry twigs and some moths resemble bees. This prevents birds from eating them. Predator-Prey Relationships (Cycle) Predator-prey relationships are characterized by oscillation of both predator and prey populations over a period of time. By oscillation, we mean there is a regular pattern of increase and decrease of populations of both predator and prey (See Figure 1.9). Generally, the predator is a carnivore, while the prey is a herbivore. However, this general truth may vary depending upon the kind of predator-prey interactions. For example, parasites become predator when they feed on their host (prey); herbivores become predator when they feed on plants (prey). Figure 1.9: Predator-prey relationship (Cycle) The main reason of oscillation is that as the predator population increases, it progressively consumes larger number of prey until the prey population starts to decline. Then the declining prey population no longer supports the large increasing predator population. As the prey population declines, the predator now faces a food shortage, and many of them starve or fail to reproduce. As a result, the predator population declines sharply to a point where the reproduction of prey more than balances its losses through predation. Eventually, the population of prey increases, which is followed by an increase in the population of predators. In this manner, there is a regular pattern of increase and decrease in the population of both prey and predator over a time period (Figure 1.9). Significance of Predation Predation Prevents a Single Species from Becoming Dominant A keystone predator is a species that reduces the density of the strongest competitors in a community. These keystone predators may feed on the dominating prey species and prevent it from becoming dominant. Thus, they are tied up to the balance of organisms in a particular ecosystem. Addition or removal of these keystone predators can have drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, in grassland, herbivores (grazers) may prevent as single dominant species from taking over. Predation can Either Increase or Decrease Species Richness In an ecological community where predator and prey exist together, predator has the ability to either increase or decrease the number of prey species. The predator changes the number of prey depends on the favourability of the environment and also on whether prey is a competitively dominant species or competitively inferior species in a community. When keystone predator feeds on dominant prey, it generally promotes species richness by releasing the inferior prey species to coexist with the dominant species. Predation as Source of Natural Selection Predation is an important factor of moulding evolution of traits for both predators and prey species. Natural selection favours the fittest individuals in a community. Thus, the process of natural selection favours predators that are more efficient in capturing prey than the less efficient predators. In the same way, the process of natural selection favours prey species that are more efficient in escaping or deterring predators than the less efficient prey species. On the one hand, predators impose strong selective force on their prey to evolve into the most efficient prey against the predators. On the other hand, prey species also counter-impose strong selective pressures on their predators to evolve into the most efficient predator against the prey. Since these selection forces are working side-by-side on both predator and prey, these two parties evolve together. Thus, coevolution is evident. The process of evolution taking place side-by-side on two closely associated species is called coevolution 1.2. 4. Saprophytism In Greek, sapro-(“putrid matter”) + phyte (“plant, growth”). The condition of certain living organisms feeding and living on dead organic matter is simply called saprophytism. It is generally exhibited by saprophytes. Saprophytes are living organisms which feed on dead organic matter such as dead plant or animal tissue. In this regard, they are detrivores. They break down organic matters in simpler forms that can be taken up and recycled by plants. Thus, they play a very important role in soil biology. Examples include most fungi (See Figure 1.10 (a) and (b), bacteria, and some orchids. Figure 1.10: (a) Mushroom (molds) (b) Bread mold, R. nigricans Most of the saprophytes lack chlorophyll, and therefore, cannot perform photosynthesis. Thus, they depend on the food energy they absorb from the decaying organic matters. This means that they are heterotrophs and are considered consumers in the food chain. They are characterized by their use of a particular kind of digestion mechanism, called extracellular digestion. In this process, they secrete digestive substances into the surrounding environment through which they break down organic matter into simpler substances. The nutrient-rich broken organic substances are then directly absorbed through the membrane of the organism’s cells and are metabolized. The example of common saprophytic fungi belongs to Rhizopus family. These fungi have an extensive network of hyphae, similar to tiny roots, which grow through the organic matter. They grow in a network called a mycelium. Mycelium helps the fungus to penetrate into the organic matter where the hyphae secrete digestive enzymes and absorb the resulting nutrients. Significance of Saprophytism Many micro saprotrophs and other decomposers, involving insects, snails and beetles help in recycling valuable nutrients from dead organic matter which is released back into the soil to be reabsorbed by plants. For example in a rainforest ecosystem, to promote healthy rainforest, nutrients such as iron, calcium, potassium and phosphorous are essentially required. The decomposers derive these essential nutrients from decaying organic matters and then release into the soil where the plants reabsorb it again. 1.2.5. Mutualism (+, +) It is an interaction of two or more species where the interacting species mutually benefit from each other. And these interacting species mutually benefit from each other so much that they become completely dependent on one another. They cannot survive and thrive without each other. That is the reason why this interaction is termed as mutualism or obligate symbiosis. Mutualism seems to replace parasitism as ecosystems evolve towards maturity, and it seems to be especially important when some aspect of the environment is limiting (such as water or infertile soil). Examples: Bees and flowers: Bees depend on flowers for food in the form of nectar and pollen. And the flowering plants depend on bees or other pollinators to carry their male reproductive cells specifically to the female parts of other flowers of the same species. In this way, bees depend on flower for food, while flower depends on bees for pollination. Significance of Mutualism Mutualism is a type of symbiosis, which means living together. The most important impact of mutualism is that the species which cannot survive individually, can survive by partnering with other individual species. By living together and depending upon each other, they could overcome harsh and unfavourable conditions and thrive in the ecosystem. Mutualism thus helps in moulding or structuring community towards better species interactions. 1.2.6. Commensalism (+, 0) It is an interaction of two or more species in which one species is benefited while the other species is neutral or is not benefited. The species which is benefitted is designated with “+” sign, while the species which is neutral is designated as “0”. In commensalism, the species which is unaffected is the host. The species that benefit from the association is called commensal. Commensal may obtain nutrients, shelter, support or locomotion from the host species. Normally, commensal relation is often between a larger host and a smaller commensal. Moreover, during the interaction, the host remains unchanged, whereas the commensal species may show great morphological adaptation. Examples: Oysters sometimes have a small, delicate crab (Figure 1.11) in the mantle cavity. These crabs are usually commensal, although sometimes they overdo their guest status by partaking of the host’s tissues. The cattle egret follows cattle (Figure 1.12), water buffalo, and other large herbivores as they graze. The herbivores flush insects from the vegetation as they move, and the egrets catch and eat the insects when they leave the safety of the vegetation. Figure 1.11: Crab inside oyster Figure 1.12: Cattle egrets and cattle Significance and Criticism of the Concept of mutualism The associations between two populations of species that result in positive effects are exceedingly widespread and are important in determining the function and structure of populations and communities. Some biologists argue that the commensal in commensalism must be likely mutualistic or parasitic in a small scale which is undetected. And it is unlikely that the host is also completely not harmed or neutral. Example: Epiphytes intercepting substantial amounts of nutrients from the host plant must be affecting the host in some other way which might be unnoticed. Application Activity 1.2 The data below shows imagined numbers of how a predator and a prey affect each other’s populations in an ecosystem over a period of several years. Year 2000 2001 2002 2003 2004 2005 2006 2007 2008 Actual number of antelopes 15 15 20 35 35 100 45 15 15 Cheetah population 10 25 20 15 10 0 0 0 0 a) Plot a graph to represent the above data. b) What conclusion can you make about the effect of the predator on the population of the prey? c) In what way does the population of prey affect the population of the predator? d) What would happen if all the predators died of a disease? e) Is relationship between prey and predator beneficial or harmful? Justify. f) How can a farmer apply the knowledge about the relationship between predators and preys, parasites and host? Skills Lab 1 Visit your school garden/school farm/ nearby farmer’s Activity; identify the biological interactions through observation. Evaluate the contribution of biological interaction in recycling matter and maintenance of equilibrium in environment. Do the report of your observation. What is your advice to the farmers who used to burns their farms in order to grow new plants in their garden?