UGC NTA NET/JRF Exam, Environmental Sciences, June-2023

The Lincoln Index is a method employed for estimating population density, particularly in wildlife ecology and conservation studies.

Named after American statistician Charles Lincoln, this index involves capturing and marking a portion of the population, releasing them back into the environment, and then recapturing a sample later.

The formula for the Lincoln Index is derived from the ratio of the marked individuals in the first sample to the total number of individuals in the second sample.

By assuming that the proportion of marked individuals in the recaptured sample is representative of the entire population, the Lincoln Index provides an estimate of population density.

(c) Reproductive effort - small: Stresstolerant (S) species exhibit a life history strategy characterized by a small reproductive effort. This means that they allocate fewer resources to reproduction compared to other species.

In stressful or resource-limited environments, where the competition for resources is high, stress-tolerant species prioritize their own survival over investing heavily in reproduction.

(e) Resource allocation to seed production - small: Stress-tolerant species typically invest fewer resources in seed production. Producing seeds is a resource-intensive process, and stress-tolerant species opt for a strategy that minimizes this investment.

By allocating fewer resources to seed production, these species prioritize resource conservation for their own maintenance and resilience in environments where resources are limited or unpredictable.

Functional food webs are characterized by their focus on the impacts of species on the structure of a community, emphasizing the functional roles and interactions among organisms within an ecosystem.

Unlike energy flow food webs that primarily highlight the transfer of energy through trophic levels or connectedness webs that emphasize linkages among species, functional food webs delve into the specific ecological functions each species performs within the community.

These functions encompass a spectrum of roles, such as pollination, decomposition, nutrient cycling, and other ecological processes that contribute to the overall structure and functioning of an ecosystem.

The quote encapsulates the perspective of H.A. Gleason, a proponent of the Individualistic Concept in ecology.

Gleason argued against a deterministic, fixed-law view of ecological succession, proposing that ecological communities do not follow rigid, predictable trajectories during the process of succession.

According to Gleason, the outcomes of succession are influenced by a myriad of factors and are contingent on the unique attributes and interactions of individual species.

The assertion that mega-biodiversity regions are concentrated in the tropics is a well-established and widely recognized ecological pattern.

The tropics, particularly regions near the equator, are characterized by an exceptional diversity of species across various taxa, including plants, animals, and microorganisms.

This high biodiversity is attributed to a combination of factors, and the reason provided (Reason R) offers a plausible explanation for this phenomenon.

Reason (R) highlights the geological history of tropical areas, emphasizing their longterm stability and the absence of glaciations.

Unlike temperate and Polar Regions that have experienced significant climatic fluctuations, tropical regions have maintained relatively consistent and favourable climatic conditions over extended geological periods.

This stability has allowed local species to evolve and adapt to their specific ecological niches, leading to the accumulation of diverse and specialized life forms.

Statement I is false because ecosystems are not closed systems. Ecosystems are, in fact, open systems that exchange energy, materials, and organisms with their external environment.

Energy flows into ecosystems from the sun and is eventually lost as heat, while materials, such as nutrients, cycle within and between ecosystems. The movement of biota, including the migration of species, also contributes to the dynamic nature of ecosystems.

Therefore, the concept of ecosystems being closed is inaccurate. Statement II is accurate. Ecosystem processes are regulated by a set of dynamic and interactive controls. Climate influences temperature, precipitation, and other environmental factors that shape the conditions within an ecosystem.

The availability of essential resources, such as water, nutrients, and sunlight, plays a crucial role in determining the structure and productivity of ecosystems.

The composition and interactions among different species, organized into functional groups based on their roles in the ecosystem, influence ecosystem processes.

(a) Habitat selection, the first mechanism, underscores the tendency of species to occupy distinct ecological niches, minimizing encounters between potentially interbreeding individuals. This segregation ensures that distinct habitats act as effective barriers to reproduction, reducing the chances of hybridization.

(b) Flowering time, primarily applicable to plants, represents another layer of reproductive isolation. Different species may exhibit significant temporal disparities in their flowering periods, ensuring that pollen transfer and fertilization occur within conspecific populations.

(c) Sexual isolation, the third mechanism, encapsulates an array of factors that hinder successful mating attempts between individuals of different species. This can involve physical, behavioural, or chemical barriers that render mating incompatible.

(d) Isolation by pollinators, the fourth mechanism, is particularly relevant for plant species relying on specific pollinators for successful reproduction.

If a particular pollinator, such as a bee species, is adapted to pollinate a specific plant species, it might not effectively transfer pollen between different plant species, thereby enforcing reproductive isolation.

Convergences represent a fascinating phenomenon in ecology where disparate species, facing analogous environmental challenges in widely separated geographical regions, independently evolve similar adaptations, morphological traits, and ecological strategies.

This process is driven by the selective pressures imposed by comparable environmental conditions, such as extreme climates, which necessitate the development of convergent traits for survival.

Despite lacking a shared evolutionary history or ancestry, these species converge towards similar ecological features, leading to the creation of vegetation that displays remarkable resemblances.

Sciophytes, or shade-adapted plants, represent a diverse group of plant species that have evolved specific features and strategies to thrive in environments characterized by reduced light availability.

The adaptations of sciophytes are a response to the challenges posed by shaded conditions, where access to sunlight is limited due to factors such as the presence of taller vegetation, dense canopies, or structures that cast shadows.

These plants have developed morphological, physiological, and anatomical characteristics to optimize their performance under lowlight conditions.