Topic 9 - Keystone Sample Quiz

The fact that young birds raised in isolation still build nests characteristic of their species suggests that nest-building behavior is genetically inherited from their parents. This means that the ability to build nests is passed down through genes, rather than being learned from watching other birds. This finding supports the idea that certain behaviors are innate and instinctual, rather than solely learned through observation and experience.

The given scenario describes the process of ecological succession. Ecological succession refers to the gradual and predictable changes in the composition and structure of an ecological community over time. In this case, the volcanic eruption destroyed the existing forest, leaving behind a barren landscape covered in volcanic ash. Over the years, small plants were able to grow in the ash, which eventually led to the formation of soil. As the soil developed, shrubs and trees were able to grow, resulting in the establishment of a new forest ecosystem. This sequence of changes exemplifies ecological succession, where a new community gradually replaces the previous one in a disturbed or barren area.

Graph 4 best represents the relative energy content of the levels of the energy pyramid. In an energy pyramid, each level represents a trophic level, with producers at the bottom and higher-level consumers at the top. The energy content decreases as you move up the pyramid due to the loss of energy through metabolic processes and heat. Graph 4 shows a clear decrease in energy content as you move up the levels, indicating the correct representation of the energy pyramid.

The change of abandoned railroad tracks being overgrown with weeds and later having small aspen trees growing in the middle is an example of ecological succession. Ecological succession refers to the process of gradual and predictable changes in the composition and structure of an ecosystem over time. In this case, the initial colonization of weeds is followed by the establishment of aspen trees, indicating a succession of plant species in response to changing environmental conditions. This process is a natural progression of ecological communities and demonstrates how ecosystems can adapt and evolve over time.

A mushroom is considered a heterotroph because it obtains nutrients from its environment. Unlike autotrophs that can produce their own food through photosynthesis, mushrooms cannot produce their own energy or nutrients. Instead, they rely on obtaining organic matter from their surroundings, such as decaying plant material or dead organisms. This makes them dependent on external sources for their nutrition, classifying them as heterotrophs.

Humans can have a significant impact on an ecological community because they have the ability to modify their environment through technology. This means that humans have the power to alter their surroundings, such as building structures, manipulating landscapes, and creating new resources. By utilizing technology, humans can change the natural balance of an ecosystem, which can have both positive and negative effects on the community. This ability to modify the environment sets humans apart from other species and allows them to have a greater influence on the ecological systems they inhabit.

Decomposers are important for supplying energy in both food chain A and food chain B. Decomposers break down dead organic matter and release nutrients back into the environment, which can then be used by producers to create energy through photosynthesis. In food chain A, the decomposers break down dead plants and animals, releasing nutrients that are used by primary consumers (herbivores) and then passed on to secondary consumers (carnivores). In food chain B, the decomposers break down dead marine organisms, releasing nutrients that are used by primary consumers (zooplankton) and then passed on to secondary consumers (fish). Therefore, decomposers play a crucial role in supplying energy in both food chains.

The energy pyramid represents the flow of energy in an ecosystem, with each level containing less energy than the one below it. In a stable ecosystem, there should be a large base of producers (plants) to support the energy needs of the consumers (herbivores and carnivores). However, in this diagram, the producer organisms are outnumbered by the consumer organisms, indicating an imbalance in the ecosystem. This suggests that there may not be enough energy available to sustain the higher trophic levels, making the ecosystem likely to be unstable.

Decomposers are necessary in an ecosystem because they make inorganic materials available to plants. Decomposers break down dead organic matter, such as dead plants and animals, into simpler inorganic compounds like nitrogen, phosphorus, and carbon dioxide. These inorganic materials are then recycled back into the soil, making them accessible to plants for growth and development. Without decomposers, organic matter would accumulate and nutrients would become locked up, hindering plant growth and disrupting the balance of the ecosystem.

The graph shows a decrease in available energy as you move up the nutrition levels in the food web. This suggests that energy is being lost at each level. The only option that explains this loss of energy is "lost as heat to the environment". This means that as energy is transferred from one level to another, some of it is lost as heat and is not available for the organisms in the food web to use.