noc19-bt09 Lecture 07-Positive Interactions

Ecological Interactions: An Overview

Introduction to Ecological Interactions

• The module begins with an introduction to ecological interactions, focusing on positive interactions in ecosystems.

• Ecological interactions are defined as the effects or impacts organisms have on each other within a community.

Competition and Its Impacts

• A tree in a forest exemplifies competition; its presence casts shade and consumes resources like water and nutrients, hindering nearby plants' growth.

• This negative interaction illustrates how one organism can adversely affect another simply by occupying space.

Positive Interactions Explained

• Conversely, the same tree provides benefits; it offers shade for animals during hot seasons and cools the surrounding area through evapotranspiration.

• These various impacts of organisms on one another are categorized as ecological interactions, which can be divided into intraspecific (within species) and interspecific (between species).

Types of Interactions

Intraspecific vs. Interspecific Interactions

• Intraspecific interactions involve impacts among individuals of the same species, such as competition among chitals.

• Interspecific interactions occur between different species; for example, if a chital affects a sambar's growth.

Harmonious vs. Inharmonious Interactions

• Harmonious (positive) interactions occur when no participating organism is harmed, while inharmonious (negative) interactions result in harm to at least one organism.

• Even if no benefits arise from an interaction but no harm occurs, it is still considered positive due to the absence of damage.

Detailed Examination of Interaction Types

Intraspecific Interactions

• Examples include colonies or societies that exhibit harmonious behaviors versus inharmonious actions like competition and cannibalism within the same species.

Interspecific Interactions

• Positive interspecific interactions include protocooperation, mutualism, and commensalism. Negative ones encompass interspecific competition where different species compete for resources.

Additional Negative Interactions

• Other forms of negative interspecific interactions include parasitism (one organism benefits at another's expense), predation (one organism eats another), and ammensalism (one harms another without benefit).

Ecological Interactions: Understanding Relationships in Ecosystems

Types of Ecological Interactions

• Competition: Involves two organisms interacting in a way that harms both. This interaction can lead to resource depletion and negative effects on both species involved.

• Ammensalism: One organism is harmed while the other remains unaffected. An example includes cattle grazing on grass, where the grass suffers from trampling without any benefit or harm to the cattle.

• Exploitation: Characterized by one organism benefiting at the expense of another. Examples include predation and parasitism, such as tapeworms feeding off a host, causing harm to it.

• Neutralism: A rare interaction where neither organism impacts the other positively or negatively. For instance, two trees may appear neutral but could be competing for resources like water underground.

• Commensalism: One organism benefits while the other is not significantly affected. An example is a crow hitching a ride on a buffalo; although there might be minimal energy expenditure for the buffalo, it generally experiences no significant impact.

Summary of Ecological Interaction Types

• The six main types of ecological interactions are competition, ammensalism, exploitation, neutralism, commensalism, and mutualism. Each type describes different dynamics between organisms within an ecosystem.

Intra-specific Interactions

Colonies and Societies

• Colonies Defined: Functional integrated aggregates formed by individuals of the same species. Examples include coral reefs and microbial colonies which function collectively despite being composed of individual organisms.

• Coral Reefs as Colonies: Coral reefs appear as single structures but consist of numerous individual corals working together as an integrated unit.

Discovery of Penicillin and Interactions in Nature

The Discovery of Penicillin

• The discovery of penicillin is illustrated through the interaction between colonies of Staphylococcus bacteria and Penicillium fungus, which releases penicillin to kill the bacteria.

Societies and Division of Labor

• Societies are defined as interactions for labor division among individuals of the same species, exemplified by bee hives where roles are strictly divided: queen bees lay eggs, drones fertilize them, and worker bees forage for food and care for larvae.

• Collaboration within these societies is essential; worker bees cannot reproduce while the queen cannot defend herself. Their interdependence allows them to pass on their genes.

• Other examples include termite mounds and wolf packs, where different members serve distinct purposes contributing to the colony's success.

Interspecific Harmonious Interactions

• Interspecific harmonious interactions occur between different species without harm. An example is protocooperation, where both parties benefit but do not rely on each other for survival.

• Protocooperation involves mutual benefits without obligatory dependence; entities can separate without affecting their survival.

Examples of Protocooperation

• A classic example includes birds eating ectoparasites off giraffes. Birds gain food while giraffes receive skin cleaning from parasites.

• This relationship illustrates that even if one party is absent (birds or giraffes), both can survive independently.

Cleaner Fishes Interaction

Understanding Ecological Interactions

Cleaning Symbiosis: Hippopotamus and Fish

• The interaction between hippopotamuses and cleaning fish involves the fish entering the mouth of the hippo to clean it, highlighting a mutualistic relationship where both parties benefit without harm.

• For this symbiotic relationship to function effectively, the fish must not perceive the hippo as a predator; otherwise, they will avoid cleaning it.

Hermit Crabs and Sea Anemones: A Case of Protocooperation

• Hermit crabs utilize vacated molluscan shells for protection due to their soft bodies, showcasing an adaptive behavior in response to predation risks.

• Sea anemones possess stinging cells that can deter predators, providing additional protection when attached to hermit crabs' shells.

• This relationship exemplifies protocooperation; while neither organism is dependent on the other for survival, both gain benefits—protection for the crab and mobility for the anemone.

Mutualism: Essential Relationships in Nature

• Mutualism is defined as a relationship where both organisms benefit and are dependent on each other for survival.

• An example includes rhizobium bacteria found in legume root nodules that provide nitrogen fixation essential for plant growth while receiving shelter and nutrients from the plant.

Commensalism: One-Sided Benefits

• Commensalism describes interactions where one organism benefits while the other remains unaffected.

Understanding Commensalism in Nature

The Concept of Commensalism

• Bacteria can provide benefits to themselves without causing harm or benefit to humans, illustrating a non-pathogenic relationship.

• Commensalism is defined as an interaction where one organism benefits while the other neither gains nor suffers. An example includes egrets feeding alongside buffalos.

Egrets and Buffalos: A Case Study

• Egrets are insectivorous birds that feed on insects found in grasses, which serve as their food source.

• Observations show egrets waiting near a wall early in the morning without foraging for food despite the presence of insects.

Energy Dynamics in Foraging

• The behavior of egrets changes when buffalos arrive; they begin to forage after observing these large animals.

• Insects are often camouflaged, making them difficult for egrets to catch without additional stimuli like movement from grazing buffalos.

Cost-Benefit Analysis of Foraging

• The energy cost of catching an insect (5 calories spent) exceeds the energy gained from eating it (3 calories), leading to inefficient foraging.

• Egrets conserve energy by remaining inactive until conditions improve, such as when buffalos disturb the grass and reveal hidden insects.

Predation Risks and Behavioral Adaptations

• The presence of potential predators like street dogs increases the risk for egrets, further discouraging them from foraging actively.

Ecological Interactions and Their Implications

Decision-Making in Chital Behavior

• The chital must decide between fleeing or continuing to feed on grass, balancing energy expenditure with food acquisition.

• As a human approaches within 50 meters, the chital perceives an increased threat and opts to flee rather than continue feeding.

Flight Distance Phenomenon

• The concept of flight distance is observed across various species, including insects that may flee from larger animals like buffaloes due to fear of being trampled.

• When buffaloes move, they inadvertently assist egrets by causing insects to jump, which the egret can then catch for food.

Commensalism Explained

• The relationship between buffaloes and egrets exemplifies commensalism; the egret benefits without harming the buffalo.

• Buffaloes tolerate egrets because they pose no threat, allowing for close proximity during their interactions.

Types of Ecological Interactions

• Ecological interactions can be classified as harmonious (beneficial for at least one party) or inharmonious (harmful to one party).

• Intra-specific interactions occur within the same species while inter-specific interactions happen between different species.

Examples of Intra-Specific and Inter-Specific Interactions

• Intra-specific competition among buffaloes can arise when resources like grass are limited, affecting survival chances.

• Societies such as honeybee colonies demonstrate cooperative behavior with division of labor among different roles (queen bee, worker bees).

Mutualism vs. Protocooperation

• Mutualism involves obligatory relationships where both organisms benefit for survival; protocooperation allows benefits but is not essential for survival.

Mutualism: A Symbiotic Relationship

Overview of Mutualism

• The relationship between rhizobium and legume plants is a prime example of mutualism, where both parties are essential for each other's survival.

• Rhizobium bacteria reside in the root nodules of legume plants, providing nitrogen as a nutrient crucial for plant growth.

• In return, the legume plants offer shelter and food to the rhizobium, creating a beneficial cycle that sustains both organisms.

• If either the rhizobium or the plant is removed from this interaction, both would ultimately perish due to their interdependence.

• This highlights the importance of harmonious interactions in ecosystems and sets the stage for discussing negative interactions in future lectures.

Transition to Negative Interactions