Problem 9 - AP Biology Premium Prep 2021

Question

Costa Rica is plentiful with many beautiful tropical rainforests. For a long time, cattle farmers cleared much of the forests for their livestock. However, in recent decades, the government has placed more emphasis on reforestation. Several fields are now being reclaimed by the rainforest. One such field has many long grasses, a few tall palms, and some dense shrubbery along the periphery of the field. This field can be said to be (A) invaded by pioneer species (B) a product of secondary succession (C) a climax community (D) filled with invasive species

Step-by-Step Solution

Answer

The short answer is: (B) a product of secondary succession.

Step 1: Understand the Options

Let's start by understanding the four given options: (A) Invaded by pioneer species: Pioneer species are the first organisms to colonize a new habitat, often in areas where there has been a recent disturbance. These plants and animals are typically hardy, fast-growing, and able to withstand harsh environmental conditions. (B) A product of secondary succession: Secondary succession is the natural process of regrowth and community development that occurs after a disturbance in an ecosystem. The disturbance may be due to a natural event, such as a fire or flood or human activities such as agriculture or logging. (C) A climax community: A climax community represents a stable and mature ecosystem that has reached the final stage of ecological succession, having undergone a series of species replacements and adaptations over time due to changes in abiotic and biotic factors. (D) Filled with invasive species: Invasive species are non-native plants, animals, or pathogens that can cause harm to an ecosystem by outcompeting native species, disrupting natural processes, or altering the environment in ways that make it less suitable for native species.

Step 2: Relate the Options to the Situation

Now, we need to determine which of these options best describes the field in Costa Rica. The field was previously cleared for cattle farming but is now being reclaimed by the rainforest, with long grasses, tall palms, and dense shrubbery growing back.

Step 3: Select the Best Option

Based on the situation given, the most appropriate answer is: (B) a product of secondary succession This is because the field is undergoing a natural process of regrowth and community development after the disturbance caused by cattle farming. The long grasses, tall palms, and dense shrubbery indicate that the ecosystem is regenerating, and native species are re-establishing themselves in the area, which is consistent with secondary succession.

Key Concepts

Secondary Succession

Secondary succession refers to the natural, gradual process of recovery and ecological regeneration in an ecosystem that has been disturbed. Unlike primary succession that begins in a lifeless area with no soil, secondary succession occurs in areas where a community has been removed; it's the rebirth of an ecosystem after a major disruption.

Imagine a wildfire burning through a forest, or in the case of the Costa Rican fields, cattle farming clearing the land. These events leave behind soil that still contains a seed bank, and possibly, surviving organisms. Over time, different species of plants and animals recolonize the area. The long grasses, tall palms, and dense shrubbery described in the Costa Rican field are part of the community that establishes during the early to middle stages of secondary succession, as the ecosystem begins the journey back to its pre-disturbance state.

Secondary succession is a testament to the resilience of nature, showcasing the ability of ecosystems to heal and regain their complex structure and biodiversity after interference, given the right conditions and enough time.

Pioneer Species

Pioneer species are ecological trailblazers, initiating the first chapter of an ecosystem's story after a disturbance. They are the hardy and undemanding species that settle and thrive in barren or disrupted environments, paving the way for later species to come.

In secondary succession, these would be the first plants—often weeds, grasses, or other fast-growing vegetation—that appear on the scene. They set to work immediately, stabilizing the soil, adding organic matter, and creating conditions that are more favorable for other, more sensitive species to eventually move in. In our Costa Rican rainforest scenario, pioneer species might include certain grasses or mosses that are particularly adept at taking root in open fields left behind after agricultural use.

These species are crucial for kick-starting the ecological recovery process. However, as conditions improve, and the soil becomes richer, these trailblazers are typically outcompeted by a succession of more diverse plants and, eventually, by more permanent residents of the ecosystem.

Climax Community

A climax community is an ecological endgame, the final act in the long and dynamic process of succession. This stage represents a mature, stable ecosystem that is theoretically self-perpetuating in the absence of significant disturbances.

In the climax community, species diversity is high, and relationships among organisms are complex. The species composition is in equilibrium with the local environment and climate. For instance, the rich biodiversity of a tropical rainforest represents a climax community—the result of many years of successive growth and change.

However, reaching a climax community can take centuries, and the concept is a bit idealized as ecosystems are constantly changing and adapting to new challenges. While the field in Costa Rica with its grasses and shrubs is well on its way, it has not yet reached the climax stage, which would eventually mirror the complex structure and diversity of the undisturbed rainforest that previously existed.

Invasive Species

Invasive species are ecological interlopers—non-native organisms that enter a habitat and begin to cause harm. These species can disrupt established ecosystems, outcompete local species for resources, and alter habitats in detrimental ways.

They often thrive because they lack natural predators in the new environment, giving them a competitive edge over native species. The result can be a loss of biodiversity, changes to soil chemistry, and even effects on local water cycles. Examples could include certain plant species that outcompete native flora or animals that predate on local wildlife.

In the agricultural fields in Costa Rica, if any foreign species were introduced that started to dominate the area, they would be considered invasive. However, since the fields are being reclaimed by native species that are typical of the local ecosystem, there is no indication from the given context that invasive species are present.