Invasive Species
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AP Environmental Science › Invasive Species
A new non-native aquarium plant is found in a local lake. It forms dense surface mats that block sunlight and reduce oxygen levels when the mats decay. Anglers report fewer native submerged plants and a decline in some fish species. Which prediction best matches the concept of competitive exclusion and ecosystem alteration by an invasive species?
Fish populations will increase because decaying mats always raise dissolved oxygen and improve habitat quality.
The aquarium plant will likely be outcompeted by native plants because non-native species are usually less tolerant of local conditions.
Native submerged plants may continue to decline as the invader monopolizes light and space, potentially shifting the lake toward lower biodiversity and altered food webs.
Native submerged plants will likely rebound quickly because invasive species generally increase resource availability for all producers.
Explanation
Invasive aquatic plants often form dense surface mats that fundamentally alter aquatic ecosystems through competitive exclusion. When these mats block sunlight from reaching the water column, native submerged plants cannot photosynthesize and die off, unable to compete for this critical resource. The ecosystem shifts toward lower biodiversity as the invasive plant monopolizes space and light. Additionally, when dense mats decay, they consume oxygen through decomposition, creating hypoxic conditions that stress fish and other aquatic organisms. This cascades through the food web, affecting fish that depend on native plants for habitat and food. Option C correctly predicts continued native plant decline through competitive exclusion and the resulting ecosystem alterations including reduced biodiversity and disrupted food webs.
A land manager removes kudzu from a site, but within a year it returns from remaining root crowns and nearby patches. Which lesson about invasive plant control does this best illustrate?
Reinvasion proves the plant is native
Invasive plants cannot spread locally once cut
Long‑term monitoring and repeated treatment are often necessary because invasives can resprout and reinvade
One-time removal is often sufficient for perennial invasives with vegetative regrowth
Explanation
Invasive plants like kudzu regrow from roots, requiring long-term monitoring and repeated treatments for control, as in option B, to prevent reinvasion and ecosystem harm. One-time removal (A) isn't sufficient, cutting doesn't stop local spread (C), and reinvasion doesn't make it native (D). This illustrates persistence in management.
A southeastern U.S. county planted kudzu (a vine native to Asia) along highway embankments in the 1930s to reduce erosion. Decades later, kudzu spreads rapidly by runners and can grow over trees, shading them out and reducing understory plant diversity. Which option best identifies the primary ecological impact of this invasive species and a realistic control approach?
It is a native pioneer species that stabilizes soils without ecological harm; the best control is to stop all mowing so it can complete succession.
It causes competitive exclusion by outcompeting native plants for light and space; integrated control can include repeated cutting/mowing plus targeted herbicide and prevention of further planting.
It increases native biodiversity by creating new habitat; the best control is to introduce additional non-native vines to compete with it.
It primarily benefits forests by increasing photosynthesis; the best control is to fertilize trees so they can grow through the vine canopy.
Explanation
Invasive species are non-native organisms that cause ecological, economic, or human health harm when introduced to new environments. Kudzu exemplifies a classic invasive plant that was intentionally introduced for erosion control but became problematic due to its rapid growth and ability to smother native vegetation. The primary ecological impact is competitive exclusion - kudzu outcompetes native plants by growing over them and blocking sunlight, which is essential for photosynthesis. This leads to reduced biodiversity as native plants die off under the dense kudzu canopy. Effective control requires an integrated approach combining mechanical removal (repeated cutting/mowing to deplete root reserves), targeted herbicide application to kill roots, and prevention of further planting. Option B correctly identifies both the competitive exclusion mechanism and realistic integrated pest management strategies.
A state agency is evaluating whether a recently introduced fish is invasive. Surveys show it is non-native, its population is rapidly increasing, and it preys heavily on native juvenile fish, reducing native recruitment. Which conclusion is best supported by these observations?
It cannot be invasive unless it causes harm to humans directly (e.g., bites or disease transmission).
It is likely invasive because it is non-native and is causing ecological harm by reducing native populations.
It is not invasive unless it also provides an economic benefit such as new recreational fishing opportunities.
It is native because any species that reproduces successfully in a region is considered native.
Explanation
The definition of an invasive species includes three key criteria: the organism must be non-native (introduced outside its natural range), it must establish self-sustaining populations, and it must cause harm to the environment, economy, or human health. This fish meets all criteria - it is confirmed non-native, shows rapid population growth indicating successful establishment, and causes ecological harm by heavily preying on native juvenile fish. The reduction in native fish recruitment represents significant ecological damage that can cascade through aquatic food webs and alter ecosystem structure. Economic or direct human harm is not required for invasive status; ecological harm alone qualifies a species as invasive. Option A correctly concludes the fish is invasive based on its non-native status and documented ecological harm to native populations.
A scientist notes that many invasive species succeed because they leave behind predators and parasites from their native range. Which hypothesis does this support?
Competitive exclusion principle (as a cause of invasion success)
Enemy release hypothesis
Milankovitch cycles
Hardy-Weinberg equilibrium
Explanation
Invasive species succeed when they escape natural enemies from their native range, allowing unchecked growth and harm to new ecosystems. The enemy release hypothesis explains this by noting reduced predation and parasitism in invaded areas, supporting option A. This leads to impacts like biodiversity loss and altered nutrient cycles. Competitive exclusion (B) is a principle but not specifically for invasion success here. Hardy-Weinberg (C) relates to genetics, and Milankovitch cycles (D) are climatic.
After zebra mussels invade, managers observe fewer zooplankton and changes in fish communities. Which explanation is most consistent with zebra mussels’ role in the food web?
Zebra mussels increase zooplankton by releasing large amounts of oxygen as a waste product
By filtering phytoplankton, zebra mussels reduce the base of the pelagic food web, indirectly affecting zooplankton and fish
Zebra mussels are top predators that directly eat fish
Zebra mussels photosynthesize and provide extra energy to zooplankton
Explanation
Invasive species like zebra mussels filter phytoplankton, depleting the pelagic food web and indirectly reducing zooplankton and affecting fish, as in option A. This causes cascading ecosystem impacts. They don't photosynthesize (B), aren't top predators (C), and don't release oxygen to boost zooplankton (D).
A lake manager considers introducing a non-native snail-eating fish to control an invasive snail. Which is the best critique of this strategy from an invasive species management perspective?
Biological control always fails and should never be considered
Introducing another non-native species can create additional invasive problems and unintended food-web impacts
The fish will only eat the invasive snail and cannot switch prey
Predators cannot affect prey populations in aquatic ecosystems
Explanation
Biological control via introducing non-native predators risks creating new invasives, as the control agent may harm non-target species or become problematic itself. This can disrupt food webs unpredictably. While it might reduce the target, alternatives like integrated management are safer. The critique highlights potential for additional invasions. Option B best articulates this risk, cautioning against hasty introductions.
A marine invasive species spreads along coastlines by releasing larvae that drift with currents. Ports with heavy ship traffic show the earliest infestations. Which spread mechanism best explains the pattern?
Ballast water discharge and hull fouling moving organisms between ports
Volcanic ash fertilization creating new habitat
Increased UV radiation causing mutation into an invasive form
Underground rhizomes spreading through soil
Explanation
Marine invasives often spread via shipping, with ballast water and hull fouling transporting larvae between ports, explaining early infestations in high-traffic areas. Currents aid larval drift, facilitating coastal expansion. This human-mediated mechanism is key to global invasions. Unlike rhizomes or natural events, shipping directly correlates with the pattern. Choice A best describes the pathway and spread.
A forest edge is invaded by kudzu, which grows fastest in full sun. Which land-use change would most likely increase kudzu spread in the region?
Increasing native plant competition through reforestation
Creating more roads and utility corridors that increase edge habitat and sunlight
Reducing soil disturbance and maintaining native groundcover
Restoring continuous forest canopy and reducing fragmentation
Explanation
Invasive species like kudzu thrive in disturbed, sunny edges, spreading rapidly and smothering natives, reducing biodiversity. Creating more roads increases such habitats, promoting spread as in option A. Restoring canopy (B), reducing disturbance (C), and increasing natives (D) would limit it.
A country requires ships to exchange ballast water in the open ocean before entering coastal ports. What is the primary goal of this policy?
To increase nutrient delivery to coastal fisheries
To prevent hurricanes from forming near coastlines
To reduce the introduction of freshwater and coastal organisms that could become invasive in new ports
To raise sea level near ports for easier docking
Explanation
Invasive species often spread through human activities like shipping, where ballast water can transport aquatic organisms to new areas, leading to ecological disruptions. Exchanging ballast water in the open ocean aims to release coastal organisms far from ports, reducing the risk of introducing species that could become invasive in new freshwater or coastal ecosystems, as in option A. This policy targets a major pathway for invasions, such as zebra mussels or Asian carp. It helps protect biodiversity and ecosystem services in ports. Option B is wrong because it doesn't increase nutrients; C and D are unrelated to ballast water's purpose.