Question

Norwegian lemmings do not live in lowland forests in Scandinavia even though they are regularly seen in these areas when their alpine populations are at high density. Suggest three hypotheses to explain the failure of lemmings to establish permanent populations in lowland forest, and discuss experiments to test these ideas. Oksanen and Oksanen (1992) discuss this question.

Short answer

The hypotheses are competition, predation, and lack of adaptation. Conduct experiments altering competition, predation, and environmental conditions to test these ideas.

Step-by-step solution

Formulate Hypothesis 1 - Competition

The first hypothesis could be that Norwegian lemmings face strong competition from other established species in lowland forests, which prevents them from establishing permanent populations. These competitor species could be better adapted to the specific resources available in the lowland areas, making it difficult for lemmings to thrive. To test this hypothesis, an experiment could be designed where the presence of potential competitor species is controlled in a specific area of the lowland forest. One could monitor and compare the establishment and survival rates of lemmings in areas with and without the competitor species.

Formulate Hypothesis 2 - Predation Pressure

A second hypothesis is that predation pressure is higher in lowland forests compared to alpine areas. Lowland environments might harbor more predators, or lemmings might be less camouflaged and thus more vulnerable there. An experiment to test this could involve creating controlled environments in the lowland forests with varying levels of predator presence. By observing the survival and reproductive success of lemmings in these different environments, one could determine the impact of predation on their establishment.

Formulate Hypothesis 3 - Environmental Adaptation

A third hypothesis might be that lemmings are not physiologically or behaviorally adapted to the specific environmental conditions found in lowland forests, such as denser vegetation, different climate conditions, or food sources. Testing this hypothesis could involve transplanting lemmings into lowland forests with conditions altered to replicate alpine conditions, such as providing similar types of food and shelter or altering climatic conditions artificially. Observing whether these conditions allow successful establishment could confirm or refute this hypothesis.

Key concepts

Species Competition

Species competition occurs when different species vie for the same resources within an ecosystem. This competition can significantly influence whether a species, like the Norwegian lemming, can establish a permanent population in a new environment. In lowland forests, existing species may have better adaptations for utilizing available resources effectively, leaving little for incoming species.

• Resource Types: These include food, water, and space.
• Competitor Dominance: Established species often monopolize these resources, making survival challenging for newcomers.

For lemmings, adapting competition dynamics is crucial. They could potentially be outcompeted by native forest dwellers who have evolved to thrive in these specific conditions. A vital method to test this hypothesis involves controlled experiments that manipulate competitor presence. By comparing lemming populations in controlled areas with and without competitor interference, researchers can gauge the impact of species competition on their survival.

Predation Pressure

Predation pressure refers to the influence predators exert on prey populations. In lowland forests, predation might be a serious obstacle for lemmings attempting to establish a permanent population. Different environments feature varying predator populations, which lemmings must navigate.

• Visibility and Camouflage: Lemmings may stand out more in unfamiliar terrains, increasing their predation risk.
• Predator Diversity: Lowland forests could support a higher number and variety of predators compared to alpine regions.

To understand how predation pressure affects lemming establishment, researchers can create controlled conditions with varying predator densities. By observing lemming survival rates and behavior within these scenarios, scientists can draw conclusions about the contribution of predation to the failure of lemmings to adapt to new habitats.

Environmental Adaptation

Environmental adaptation is an organism's ability to thrive in specific habitats due to physiological or behavioral traits. The inability of lemmings to permanently settle in lowland forests might stem from an adaptation challenge to these environments.

• Habitat Differences: Alpine environments provide unique climatic and vegetative conditions not present in lowland forests.
• Adaptation Strategies: Lemmings might lack the necessary strategies to cope with dense vegetation or different climate regimes.

Experiments to test these aspects could involve adjusting environmental conditions to mimic alpine habitats within lowland forests. By altering factors such as food availability, vegetation density, and climate, and observing lemming responses, researchers can assess their adaptive flexibility. Finding ways to facilitate lemming adaptation could assist in overcoming environmental barriers for successful establishment.