Question

Lake Baikal in Siberia is an ancient unglaciated temperate lake and contains 580 species of bottom-dwelling invertebrates. Great Slave Lake, a comparably sized lake that is at the same latitude in northern Canada and was once glaciated, contains only four bottom-dwelling invertebrate species. This observation supports which of the following hypotheses? a. species-time b. species-area c. species-productivity d. both a and b e. both b and c

Short answer

The observation supports the species-time hypothesis (choice a).

Step-by-step solution

Understand each hypothesis

Each of the hypotheses represents a different perspective on what influences biodiversity. The species-time hypothesis suggests that older habitats have more species because more time allows for more speciation. The species-area hypothesis suggests biodiversity increases with the size of the area of the habitat. The species-productivity hypothesis suggests that sites of higher productivity will support more species because more resources, like food, allow for more individuals and species.

Apply the hypotheses to the lakes comparison

In the case of Lake Baikal and Great Slave Lake, the biodiversity difference is not due to the size of the area (both are similarly sized) nor their productivity (the question give no specifics about this factor). Therefore, the species-area and species-productivity hypotheses are unlikely. However, the 'age' factor is relevant - Lake Baikal is listed as ancient and unglaciated, compared to Great Slave Lake, which was once glaciated (ie. is younger). As such, the biodiversity difference might be due to the species-time hypothesis, which argues more time allows for more species.

Finalize the answer

As per the deductions in previous steps, the observed biodiversity difference between Lake Baikal and Great Slave Lake can be best explained by the species-time hypothesis.

Key concepts

Biodiversity

Biodiversity refers to the variety of life forms within a given habitat, ecosystem, or the entire planet. It encompasses all species of plants, animals, fungi, and microorganisms. The richer or more diverse an ecosystem is, the more stable it tends to be, providing benefits such as resilience to environmental changes and resources for food and medicine. In the comparison of Lake Baikal and Great Slave Lake, biodiversity is clearly illustrated by the number of bottom-dwelling invertebrate species in each lake. When a habitat supports a wide range of species, it indicates not just a long period of species development but also healthier interactions among these species. Biodiversity further fosters the ecological roles and relationships, such as predator-prey dynamics, which maintain ecological balance.

Speciation

Speciation is the evolutionary process where new biological species arise. It occurs when groups within a species become isolated for long enough that they evolve distinct traits and begin to differ genetically. The isolation might be geographic, ecological, or due to other factors that separate groups.

• Geographic isolation can lead to allopatric speciation, where physical barriers separate populations.
• Sympatric speciation occurs without physical separation, often through natural selection or genetic mutation.

In the context of Lake Baikal, its ancient nature provided excess time for speciation to occur among bottom-dwelling invertebrates, leading to a rich diversity of 580 species. In contrast, Great Slave Lake, being much younger, did not have as much time for such developments, demonstrating fewer species.

Habitat Age

The concept of habitat age pertains to how long a particular habitat has existed without significant disruptions. This time availability often correlates with biodiversity levels, as older habitats provide grater opportunity for species to evolve and adapt. Lake Baikal is renowned for being one of the world's oldest lakes, remaining unglaciated through historical climate changes, which allowed continuous biological evolution.

• Older habitats, like Lake Baikal, typically support higher species richness.
• Younger habitats, like Great Slave Lake, have less time for speciation and adaptions to reach maturity.

Habitat age is a critical factor in the species-time hypothesis, which underlines the correlation between time and biodiversity.

Bottom-dwelling Invertebrates

Bottom-dwelling invertebrates, often referred to as benthic invertebrates, play crucial roles in aquatic ecosystems. These organisms, which include species such as worms, crustaceans, and mollusks, help with nutrient cycling, water filtration, and serve as food for other aquatic animals. In the case of Lake Baikal and Great Slave Lake, the disparity in the number of bottom-dwelling invertebrate species illustrates the impacts of habitat age and ecological history. Lake Baikal's 580 species highlight a rich benthic diversity due to prolonged and uninterrupted evolutionary processes, while Great Slave Lake's mere four species underscore the comparatively limited time available for evolutionary diversification. Understanding bottom-dwelling invertebrates is key to appreciating broader ecological and evolutionary dynamics in aquatic habitats.