Ecological Interactions Quiz

Interspecific Interactions

• Organisms engage in various interspecific interactions, including competition, predation, herbivory, parasitism, mutualism, and commensalism.
• Interactions can have positive, negative, or neutral effects on the survival and reproduction of the species involved.

Competition

• Competition occurs when individuals of different species utilize the same limited resources, impacting both their survival and reproduction.
• Intraspecific competition refers specifically to competition between members of the same species.
• Examples include weeds competing with garden plants for nutrients and lynx competing with foxes for prey.

Competitive Exclusion

• G.F. Gause's experiments demonstrated that two species competing for the same resources cannot coexist indefinitely; one will outcompete the other, leading to competitive exclusion.
• A species with a reproductive advantage will eliminate the inferior competitor over time.

Ecological Niches

• An organism's ecological niche encompasses the biotic and abiotic resources it uses, including habitat, activity periods, and food sources.
• Two species cannot permanently coexist if their niches are identical; however, resource partitioning allows similar species to coexist by utilizing different resources or times.
• The realized niche is the portion of the fundamental niche occupied by a species in a community.

Resource Partitioning and Character Displacement

• Species can partition their niches in both spatial and temporal dimensions.
• Example: Anolis lizards in the Dominican Republic differentiate their perching locations to reduce competition.
• Character displacement occurs when sympatric populations of similar species show morphological differences, as seen in Galápagos finches with varying beak depths.

Exploitation Interactions

• Exploitation refers to interactions where one species benefits at the expense of another, including predation, herbivory, and parasitism.
• Predation involves a predator killing and consuming prey, shaping adaptations in both predators and prey through natural selection.

Predator-Prey Adaptations

• Predators have acute senses, physical adaptations like fangs or claws, and behaviors that enhance hunting success.
• Prey species develop defenses such as fleeing, camouflage, or warning coloration to evade predators.

Mimicry

• Batesian mimicry occurs when a harmless species resembles a harmful one, increasing its survival rate by deceiving predators.
• Müllerian mimicry involves multiple unpalatable species resembling one another, aiding predators' learning to avoid them.
• The mimic octopus showcases advanced mimicry abilities, imitating various marine animals to evade threats and capture prey.

Cane Toad Experiment

• Researchers studied the effects of cane toads on native red-bellied black snakes in Australia, observing adaptations and changes in predation behavior after prolonged exposure to the toads.
• The experiment revealed a selective effect of cane toads on snake behavior.

Defensive Adaptations

• Various defensive adaptations, including mechanical (porcupine quills) and chemical defenses (skunk spray), evolve in species to deter predators.
• Bright coloration (aposematism) signals toxicity, while cryptic coloration helps prey blend into their environment.

These notes encapsulate the essential concepts and examples related to interspecific interactions and their ecological implications.### Herbivory

• Herbivory involves organisms (herbivores) consuming parts of plants or algae, causing harm but typically not death.
• Invertebrates, such as grasshoppers and caterpillars, represent a larger portion of herbivores compared to large mammals like cattle and buffalo.
• Marine herbivores include species like sea urchins and some tropical fish, exemplifying herbivory in ocean ecosystems.
• Many herbivores have evolved specialized adaptations, including chemical sensors to assess plant toxicity and nutritional value.
• Mammalian herbivores often utilize scent to discriminate among plant types and can prefer specific plant parts.
• Plants defend themselves against herbivores with chemical toxins (e.g., strychnine, nicotine) and physical structures like thorns and spines.

Parasitism

• Parasitism is an exploitative interaction where a parasite derives nourishment from a host, causing harm.
• Internal parasites are termed endoparasites (e.g., tapeworms) while external ones are called ectoparasites (e.g., ticks).
• Approximately one-third of Earth's species are estimated to be parasites, highlighting their prevalence.
• Some parasites exhibit complex life cycles requiring multiple hosts (e.g., the blood fluke uses humans and freshwater snails).
• Certain parasites can alter their host's behavior to facilitate transmission to the next host, enhancing their lifecycle success.
• Parasites significantly influence host survival, reproduction, and population density, such as ticks affecting moose health and predation risk.

Positive Interactions

• Positive interactions between species can involve mutualism and commensalism, benefiting at least one species without harming others.
• Mutualism is defined as a reciprocal relationship where both species benefit (e.g., ants and acacia trees).
• Mutualisms can include nutrient exchange (fungi and plant roots) and collaborative survival strategies (e.g., animal pollination).
• Costs are also associated with mutualisms; each partner gives up some resources for mutual benefit.
• Commensalism occurs when one species benefits while the other is unaffected, such as wildflowers thriving in forest shade without impacting tree health.
• Ecological interactions can shift over time, with commensal relationships transforming into mutualistic ones under changing conditions.

Community Impacts

• Positive interactions can dramatically shape ecological communities; for example, black rush (Juncus gerardii) creates favorable soil conditions in salt marshes.
• Juncus reduces soil salt concentration and increases oxygen levels, thereby enhancing biodiversity by supporting more plant species.
• The removal of beneficial species like Juncus can lead to decreased plant community diversity.

Equilibrium vs. Nonequilibrium Perspectives

• Traditional ecological views held that biological communities are stable and at equilibrium, primarily influenced by competition among species.
• Stability signifies a community’s ability to maintain a constant species composition, with the climax community seen as shaped by climate alone.
• Some ecologists questioned this, arguing that various factors (soils, topography) result in multiple stable community configurations, not just one climax community.
• Communities can be perceived as random species assemblies based on similar abiotic needs rather than functioning as cohesive units.

Disturbance and Community Dynamics

• Disturbance alters community structure by removing organisms or changing resource availability, with examples including storms, fires, floods, and human activities.
• High disturbance intensity or frequency usually decreases species diversity, while low disturbance allows dominant species to exclude others.
• The intermediate disturbance hypothesis posits that moderate disturbance levels promote greater species diversity than extreme low or high disturbance levels.

Evidence Supporting the Intermediate Disturbance Hypothesis

• Studies in New Zealand showed that invertebrate species richness was highest in streams with moderate flooding intensity, validating the hypothesis.
• Small-scale disturbances create diverse habitats, whereas large disturbances, such as significant fires, can rejuvenate ecosystems adapted to such events.

Case Study: Yellowstone National Park

• Lodgepole pine forests in Yellowstone rely on periodic fires; cones only release seeds when exposed to intense heat, fostering regrowth after fires.
• Post-1988 fires, areas within Yellowstone rapidly regrew, showcasing community adaptation to large-scale disturbances, supporting nonequilibrium community models.

Ecological Succession Overview

• Ecological succession describes species turnover in communities following disturbances, with primary succession starting in lifeless areas (e.g., after glacial retreats).
• Primary succession involves initial colonization by simple organisms like prokaryotes and protists, followed by lichens, mosses, and then vascular plants as soil develops.
• Facilitation, inhibition, or independence describes interactions between early-arriving and later species during succession.

Primary Succession Research: Glacier Bay

• Glacier Bay studies reveal a sequence of colonization post-glacial retreat, starting with pioneering species leading to a dense forest over centuries.
• Nitrogen-fixing species like Dryas play a crucial role in enhancing soil quality, gradually promoting biodiversity during succession.

Secondary Succession and Human Impact

• Secondary succession occurs after major disturbances that leave some organisms intact, leading to recolonization akin to the original community structure.
• Human activities significantly disrupt ecosystems, leading to habitat loss such as in prairies and tropical rain forests, impacting biodiversity.
• Ocean trawling poses severe threats to marine ecosystems, comparable to land deforestation, further reducing species diversity globally.

Test your knowledge on different types of ecological interactions. This quiz covers relationships such as commensalism, competition, mutualism, and more. See if you can identify how these interactions impact species in an ecosystem.