Question

In Lack's study of passerine birds in Britain, different species seem to segregate based on resource factors, such as location of prey items. This differentiation among the niches of passerine birds is known as a. competitive exclusion. b. intraspecific competition. c. character displacement. d. resource partitioning. e. allelopathy.

Short answer

The correct answer is d. Resource partitioning. This term best describes how different species of passerine birds are segregating based on factors like location of prey items, thus allowing for coexistence in the same community.

Step-by-step solution

Understand the Given Concepts

First, it's important to understand what these ecological terms mean. 'Competitive exclusion' refers to the principle that two species competing for the same resources cannot stably coexist. 'Intraspecific competition' refers to competition within the same species. 'Character displacement' refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur but are minimized or lost where the species’ distributions do not overlap. 'Resource partitioning' would refer to the differentiation of niches that enables similar species to coexist in a community. Lastly, 'allelopathy' is a biological phenomenon by which an organism produces one or more bio-chemicals that influence the germination, growth, survival, and reproduction of other organisms.

Analyze the Scenario

Lack's study shows that different species of passerine birds segregate based on resource factors such as the location of prey items. They are differentiating their niches or ecological roles based on these resources.

Match the Correct Term

With the situation and terms understood, it can be concluded that this scenario is an example of 'resource partitioning', as this term best describes a situation where species differentiate their ecological roles or niches based on variations in resources, allowing them to coexist in the same community.

Key concepts

Niche Differentiation

Niche differentiation is a process that allows species with similar needs to coexist without competitively excluding one another. It involves a distinct division of resources or habitat among species, allowing them to occupy different niches. This differentiation reduces direct competition and can be crucial for maintaining biodiversity in an ecosystem.
For example, if two bird species feed on the same type of insects but one species does it during the morning and another in the afternoon, they are engaging in niche differentiation. This subtle yet significant variation in their ecological roles allows both to thrive in the same habitat by reducing competition for the same food resources.
Understanding niche differentiation is essential in ecology as it helps explain how biodiversity is sustained. It shows the fine balance ecosystems maintain, allowing multiple species to flourish.
Some key aspects of niche differentiation include:

• Habitat differentiation: Using different areas or microhabitats to reduce overlap.
• Temporal differentiation: Active at different times to avoid direct competition.
• Dietary differentiation: Feeding on different types of food.

Passerine Birds

Passerine birds, often referred to as "perching birds" or "songbirds," consist of more than half of all bird species. They are characterized by their toe arrangement, which facilitates perching, and many are known for their vocal abilities. Passerines are highly diverse and inhabit a wide range of ecosystems around the world.
In the context of niche differentiation, passerine birds often showcase this principle vividly. By adapting to different niches, they can live in similar habitats without outcompeting each other for food or nesting space.
Some interesting characteristics of passerine birds include:

• Diverse diet: Ranging from insects to seeds and fruit, aiding in niche differentiation.
• Complex songs: Used for communication and mating, often leading to niche partitioning based on sound frequency or time of day.
• Adaptive beaks: Evolved to exploit specific food sources, assisting in niche specialization.

Competitive Exclusion

The competitive exclusion principle suggests that two species competing for the same limiting resources cannot coexist indefinitely. Eventually, one species will outcompete and exclude the other from the niche.
This principle is fundamental in understanding the dynamics of ecological communities. It emphasizes that when two species have overlapping niches, competition will drive adaptations or lead to the displacement of one species.
A classic example of competitive exclusion occurs when two species of birds compete for the same nesting sites. Over time, one might become more dominant, either driving the other to adapt or relocate.
Some key considerations of competitive exclusion include:

• Strong competition: Intensifies if niches are highly overlapping.
• Interspecific interactions: Interactions with other species can influence the outcomes.
• Adaptation and evolution: Pressures from competition may lead to character displacement or extinction.

Character Displacement

Character displacement is an evolutionary phenomenon observed when two similar species inhabit the same geographic area. This leads to differences in traits such as morphology, behavior, or ecological strategies, allowing them to coexist by reducing niche overlap.
When species compete for similar resources, natural selection favors those individuals in each species that differentiate away from the competition. This results in less competition and allows for species to coexist more effectively.
An example of character displacement is seen in Darwin's finches on the Galápagos Islands. When different species of these finches live on the same island, their beak sizes tend to diverge due to competition for food. However, when they live on separate islands, beak sizes are more similar.

• Morphological changes: Physical adaptations that reduce competition.
• Behavioral shifts: Changes in feeding habits, mating calls, etc.
• Geographic context: More pronounced in overlapping ranges, less so where species do not co-occur.