noc19-bt09 Lecture 08-Negative Interactios

Ecological Interactions: Understanding Negative Interactions

Overview of Previous Lecture

• The previous lecture covered six types of ecological interactions, focusing on both negative and positive interactions.

• Key negative interactions discussed include Competition, Amensalism, and Exploitation.

Types of Ecological Interactions

Negative Interactions

• Competition: Both organisms involved are harmed; this is a classic example of a negative interaction.

• Amensalism: One organism is harmed while the other remains unaffected, categorizing it as a negative interaction.

• Exploitation: Involves harm to one organism while benefiting another; includes predation and parasitism.

Positive Interactions

• Neutralism: Neither organism is harmed or benefited; considered harmonious.

• Commensalism: One party benefits without harming the other (e.g., egrets feeding alongside buffalos).

• Mutualism: Both parties benefit from the interaction; includes Protocooperation as a variant.

Inharmonious Interactions in Detail

Intraspecific vs. Interspecific Interactions

• Intraspecific Interaction: Occurs between individuals of the same species. Examples include:

• Intraspecific Competition: Members compete against each other for resources (e.g., humans competing with humans).

• Cannibalism: One individual consumes another of the same species (e.g., black widow spiders).

• Interspecific Interaction: Occurs between different species. Examples include:

• Interspecific Competition: Different species compete for resources (e.g., chital competing with sambar).

• Parasitism & Predation: One organism benefits at the expense of another (e.g., parasites living off hosts).

Focus on Competition

Definition and Implications

• Competition defined as an ecological interaction where individuals share or partially overlap their ecological niches.

• Example provided includes two insectivorous birds sharing similar feeding grounds, leading to competition for food resources.

Understanding Competition in Ecology

Types of Competition

• Definition of Environmental Resources: Environmental resources include food, shelter, physical space, mates, access to water, and sunlight. These resources are subject to competition among organisms.

• Intraspecific vs. Interspecific Competition:

• Intraspecific competition occurs between members of the same species.

• Interspecific competition occurs between members of different species.

• Exploitative vs. Interference Competition:

• Exploitative competition involves organisms using the same resource, reducing availability for others.

• Interference competition occurs when one organism prevents another from accessing a resource without directly exploiting it.

Examples of Competition

• Exploitative Competition Example: Animals grazing on the same grassland exemplify exploitative competition; if one animal consumes most grass, less is available for others.

• Interference Competition Example: A dog preventing herbivores from accessing grassland illustrates interference competition; the dog does not consume grass but blocks access to it.

Apparent Competition

• Definition and Example: Apparent competition arises when an increase in one species (e.g., red fish) leads to increased predation on another species (e.g., green fish), even though they do not compete directly for resources.

• Impact on Predator Dynamics: As red fish multiply, predators (like birds) have more food available and can reproduce more rapidly, leading to increased predation on both red and green fish.

Ecological Interaction Recap

• Competition Overview: The ecological interaction known as competition occurs when individuals share or partially overlap their ecological niches, leading to contention over environmental resources.

Case Study: Penguins at Boulder Beach

• Penguin Nesting Behavior: African penguins at Boulder Beach exhibit territorial behavior by maintaining a "pecking distance" to avoid conflict while nesting. This distance is crucial for laying eggs and raising chicks.

Understanding Dominance and Recessiveness in Animal Behavior

Dominant vs. Recessive Behaviors

• The discussion begins with the distinction between dominant and recessive behaviors in animals, illustrated through a bird's display of dominance by raising its neck while others remain submissive.

• Observations are made on penguins fighting for territory, highlighting how dominant birds assert their presence while recessive ones exhibit submissive behavior.

Competition for Mates Among Black Bucks

• The focus shifts to male black bucks competing for access to a female, emphasizing that the resource at stake is not space or food but rather mating opportunities.

• The method of competition involves physical confrontation using their long antlers, showcasing natural selection in action as one buck displaces another from proximity to the female.

Consequences of Resource Competition: Habitat Displacement

Habitat Displacement Explained

• Habitat displacement occurs when external factors, such as human intervention (e.g., cattle grazing), force native species like black bucks out of their prime habitats.

• When herdsmen introduce cattle into the area, they compete for the same nutritious grasses that sustain black bucks, leading to potential harm or displacement of these animals.

Prime vs. Subprime Habitats

• A clear distinction is made between prime habitats (flat terrain with ample resources) and subprime habitats (rocky areas lacking sufficient food and shelter).

• The phenomenon illustrates how human activities can disrupt natural ecosystems by forcing wildlife into less suitable environments.

Niche Differentiation and Human Impact

Niche Differentiation

• In nature, different species occupy specific niches; for example, black bucks thrive in grasslands while sambars prefer rocky terrains.

• Human encroachment complicates this balance by displacing animals from their natural habitats, disrupting established ecological relationships.

Types of Competition in Ecology

Exploitative vs. Interference Competition

• Two types of competition are defined: exploitative competition involves multiple organisms vying for limited resources (e.g., grassland), whereas interference competition occurs when individuals prevent others from accessing those resources.

Competition for Resources in Ecology

Types of Competition

• Interference vs. Exploitative Competition: Interference competition occurs when individuals contest the same resource without using it, while exploitative competition involves direct consumption of resources, making them unavailable to others.

• Examples of Competition: In interference competition, one species may prevent another from accessing a resource (e.g., a dog barking to keep cows away), whereas in exploitative competition, an individual directly consumes the resource (e.g., a cow eating grass).

The Dog in the Manger Analogy

• Analogy Explanation: The phrase "dog in the manger" illustrates interference competition where an organism prevents others from utilizing a resource it does not consume itself.

• Conflict Dynamics: In exploitative competition, there is no direct conflict as organisms simply consume resources; however, interference involves direct interactions and conflicts between competing species.

Competitive Ability

• Defining Competitive Ability: For exploitative competition, competitive ability is measured by the rate at which an individual consumes resources (e.g., how much grass a cow eats).

• Aggression in Interference Competition: In contrast, competitive ability in interference competition relates to aggressive behaviors or displays that deter competitors (e.g., barking or fighting).

Impact on Carrying Capacity

• Carrying Capacity Explained: Carrying capacity refers to the maximum number of individuals that can be supported by available resources. Increased availability leads to higher carrying capacity.

• Effects of Exploitative Competition: Pure exploitative competition reduces carrying capacity as one species depletes resources needed by others.

Modeling Competition Effects

• Interference's Impact on Reproduction Rates: Pure interference competition can reduce reproductive rates even if resources are present. For example, more grass might be required for offspring due to increased aggression among competitors.

• Non-linear Relationships in Exploitative Competition: The relationship between population growth rates and resource availability is non-linear; more individuals lead to diminishing returns on growth due to reduced access to shared resources.

Examples of Competitions

Competition in Ecology

Intraspecific Competition

• Intraspecific competition occurs when individuals of the same species, such as cows, compete for limited resources like grassland. This type of competition is exploitative as each cow's grazing reduces the availability of grass for others.

Interspecific Competition

• Interspecific competition involves different species competing for the same resource. For example, cows and buffalos grazing on the same grassland exemplify this type of competition.

• Canopy trees from various species compete for sunlight in a forest setting. A tree casting shade limits access to sunlight for saplings of other species, demonstrating interspecific exploitative competition.

• The presence of a larger canopy tree can significantly reduce survival chances for smaller saplings by limiting their access to sunlight.

Interference Competition

• Interference competition can occur within a species (intraspecific), where one individual displays territorial behavior against another. For instance, penguins may aggressively defend space from conspecifics even if they do not need that much territory.

• An example includes a penguin preventing another from accessing resources through aggressive behavior, illustrating direct interaction and conflict over space.

Allelopathy

• Allelopathy refers to chemical interactions between plants where one species releases substances that inhibit the growth of another. For instance, tree leaves may release chemicals into the soil that harm saplings of different species while allowing their own kind to thrive.

• Fungal colonies like penicillium produce antibiotics that kill nearby bacterial colonies, showcasing allelopathy in action through chemical warfare between different organisms.

Apparent Competition

• Apparent competition describes an interaction between two prey species sharing a common predator. For example, an increase in sambar population leads to more tigers preying on both sambars and chitals due to increased food availability.

• The relationship illustrates indirect competition; as one prey population increases (e.g., sambars), it indirectly decreases another (e.g., chitals), mediated by predation pressure from shared predators like tigers.

Understanding Apparent Competition in Ecosystems

Generalist Species and Food Limitation

• A generalist species is not selective about its diet, consuming various food sources (A and B), which makes it food-limited.

• In scenarios where a predator population (P) is limited by factors other than food, such as disease, increases in prey populations (A) do not affect the predator population or decrease other prey populations (B).

Keystone Species: The Role of Fig Trees

• Some prey species, like fig trees, act as keystone species due to their significant ecological impact relative to their abundance.

• Fig trees provide diverse edible parts (leaves, fruits, flowers), serving as crucial food sources during dry seasons when other foods are scarce.

Impact of Fig Trees on Bird Populations

• An increase in fig tree numbers leads to a rise in bird populations that feed on them; these birds subsequently consume other nearby edible plants.

• Despite being keystone species, fig trees can create apparent competition with other plant species by supporting higher bird populations that may decimate those plants.

Apparent Competition and Community Dynamics

• Prey species can be excluded from communities through diffused apparent competition; some may even face extinction due to predation pressures.

• Examples include insect host-parasitoid dynamics where increased insect populations lead to more parasitoids that negatively impact other insect species.

Invasive Species and Feedback Loops

• Lantana, an invasive shrub from Africa, produces abundant fruits consumed by birds; this leads to increased bird populations that further threaten native plant species.

• Bamboo flowering results in nutritious seeds that boost rodent populations; these rodents then feed on various plant species, exemplifying apparent competition.

Trophic Cascades and Top-down Regulation

• Apparent competition reduces equilibrium densities and growth rates of prey species within food webs; it highlights predator-prey dynamics.

• Trophic cascades illustrate how top predators influence lower trophic levels. For instance, increasing bird numbers can decimate shrubs affected by invasive plants like lantana.

Invasive Species and Ecological Interactions

The Impact of Lantana on Ecosystems

• Lantana, an invasive species, thrives in ecosystems where other shrubs have died off, creating space for its rapid spread. This leads to a decline in native species as they are outcompeted.

• The introduction of lantana creates a positive feedback loop that allows it to colonize new areas by negatively affecting established species, which can be preyed upon by birds.

Cannibalism and Parasitism

• Cannibalism is defined as one individual consuming another of the same species. Examples include sexual cannibalism seen in black widows and praying mantises.

• Parasitism involves one organism living at the expense of another. Ectoparasites (like leeches) live outside their hosts while endoparasites (like Plasmodium vivax causing malaria) reside inside.

Predation Dynamics

• Predation is characterized by one organism killing another for food. An example includes birds preying on centipedes, illustrating the predator-prey relationship.

• Plants also exhibit predatory behavior; pitcher plants attract insects with sugary secretions and trap them within their structure.

Amensalism: A Unique Interaction

• Amensalism occurs when one organism harms another without gaining any benefit or suffering harm itself. An example is grass being trampled by animals like black bucks without direct feeding.

• This interaction highlights how ecological relationships can be complex, with some organisms inadvertently harming others through their natural behaviors.

Negative Interactions in Ecology

Understanding Negative Interactions

• The lecture contrasts previous discussions on positive interactions with a focus on negative interactions, which can occur either within the same species (intraspecific) or between different species (interspecific).

• A primary example of negative interaction is competition, which can manifest as:

• Interference competition

• Exploitative competition

• Apparent competition

• Other forms of negative interactions include parasitism, predation, and amensalism. Studying these interactions is vital for understanding ecological systems.

Importance of Interaction Studies

• Analyzing how different populations interact helps elucidate ecosystem dynamics and the relationships among community members.