What is the primary difference between a non-native species and an invasive species?

While both are introduced to a new area by humans, a non-native species may be harmless or beneficial. An invasive species is specifically defined by its ability to cause ecological, economic, or human health harm.

Why are r-selected species more likely to become successful invaders than K-selected species?

r-selected species have high reproductive rates, mature quickly, and produce many offspring. This allows them to establish large populations rapidly and recover quickly from control efforts or environmental fluctuations.

How does the 'Enemy Release Hypothesis' explain the success of invasive species?

It suggests that invasive species leave behind their natural predators, pathogens, and competitors in their native range. In the new environment, they face fewer 'top-down' population controls, allowing them to outcompete native species.

What is a common error when assuming the impact of a non-native crop species?

The error is assuming all non-native species are harmful. Many agricultural crops and livestock are non-native but do not spread aggressively or disrupt ecosystems, meaning they are not classified as invasive.

What is the main risk associated with using biological control to manage an invasive species?

The introduced biological control agent (like a predator or parasite) may shift its diet and begin preying on or infecting native, non-target species. This can create a secondary ecological crisis that is difficult to reverse.

Why is physical removal often ineffective for large-scale invasive plant infestations?

Physical removal is extremely labor-intensive and may inadvertently spread seeds or root fragments, leading to further growth. For large areas, the cost and manpower required usually exceed the available resources.

Define 'Hybridization' in the context of invasive species.

Hybridization occurs when an invasive species breeds with a closely related native species. This leads to genetic dilution, where the unique genetic identity and adaptations of the native population are lost.

What is 'Ballast Water' and how does it relate to invasive species?

Ballast water is water taken up by large ships for stability; when discharged in distant ports, it often releases non-native aquatic organisms. This is one of the most common pathways for the unintentional introduction of invasive aquatic species.

What does 'Biotic Resistance' mean?

Biotic resistance is the ability of a diverse, healthy native community to resist invasion. High species richness means more niches are filled, leaving fewer resources available for an incoming invasive species to exploit.

How do invasive species typically affect local food webs?

They can act as 'top-down' disruptors by preying on native species that have no defenses, or 'bottom-up' disruptors by consuming primary producers. This often leads to a decrease in overall biodiversity and can cause a trophic cascade.

Invasive Species | College Board AP Environmental Science

Revision Notes

College Board

Environmental Science

Unit 9: Global Change

Invasive Species

Summary

Invasive species are non-native organisms that cause ecological or economic harm in their new environment. Their success is typically driven by high reproductive rates, generalist niches, and a lack of natural predators, leading to significant biodiversity loss and ecosystem instability.

1. Definition & Core Concepts

An invasive species is defined as an organism that is introduced to an environment outside its natural geographic range and subsequently causes harm to the economy, environment, or human health. While many species are moved by humans, only those that spread aggressively and disrupt local systems are classified as invasive.

The introduction of these species can occur intentionally, such as for pest control or agriculture, or unintentionally, such as through ballast water in ships or hidden in international cargo.

A critical distinction exists between non-native and invasive; many non-native species (like certain crops) are beneficial or neutral, whereas invasive species actively outcompete native flora and fauna.

2. Biological Characteristics of Success

Invasive species are frequently r-selected species, meaning they have high reproductive rates, mature early, and produce many offspring with minimal parental care. This allows their populations to expand exponentially before native species or human interventions can respond.

They are typically generalist species that can thrive in a wide variety of environmental conditions and consume diverse food sources. This flexibility allows them to occupy niches that more specialized native species cannot maintain under stress.

The Enemy Release Hypothesis explains that invasive species often thrive because they lack the natural predators, competitors, or parasites found in their home range. Without these 'top-down' pressures, their population growth remains unchecked.

The Invasion Curve showing that as time passes, the population grows exponentially and the cost/difficulty of control shifts from prevention to long-term management.

3. Ecological Impacts

Resource Competition: Invasive species often outcompete natives for limited resources such as sunlight, water, nutrients, and nesting sites. For example, fast-growing invasive plants can create dense canopies that shade out native seedlings, leading to a monoculture.

Predation and Lack of Defenses: Native prey species often lack evolved 'anti-predator' behaviors or physical defenses against a newly introduced predator. This can lead to rapid declines or extinctions of native populations that are unprepared for the new threat.

Genetic Dilution: In some cases, invasive species can interbreed with closely related native species. This hybridization results in the loss of unique genetic traits in the native population, effectively 'diluting' the native gene pool over generations.

4. Control and Management Strategies

5. Key Distinctions

6. Exam Strategy & Tips

Invasive Species

Summary

1. Definition & Core Concepts

2. Biological Characteristics of Success

The Invasion Curve showing that as time passes, the population grows exponentially and the cost/difficulty of control shifts from prevention to long-term management.

3. Ecological Impacts

4. Control and Management Strategies

Physical Control: This involves the manual or mechanical removal of invasive species, such as pulling weeds, trapping animals, or installing barriers. While effective for small, localized populations, it is often labor-intensive and expensive for large-scale infestations.

Chemical Control: The use of herbicides, pesticides, or piscicides can target invasive populations. However, this method carries the risk of non-target effects, where the chemicals harm native species or contaminate local water supplies.

Biological Control: This strategy introduces a natural enemy (predator or parasite) from the invasive species' home range to regulate its population. This requires rigorous testing to ensure the control agent does not become invasive itself and attack native organisms.

5. Key Distinctions

Understanding the difference between various species classifications is vital for ecological management and exam performance.

Category	Origin	Impact on Ecosystem
Native	Naturally occurring in the area	Balanced through co-evolution
Non-Native	Introduced by humans	Can be neutral, beneficial, or harmful
Invasive	Introduced by humans	Aggressively harmful; disrupts balance
Endemic	Found only in one specific area	Highly vulnerable to invasive species

6. Exam Strategy & Tips

Identify the 'Harm': On exams, do not assume a species is invasive just because it is non-native. Look for evidence of 'outcompeting', 'disrupting food webs', or 'economic loss' to justify the classification.
Connect to Life History: Relate invasive success to $r$ -selection. If a question describes a species with many offspring and rapid growth, it is a prime candidate for becoming invasive.
Evaluate Control Risks: When asked about biological control, always mention the risk of the control agent attacking non-target native species. This is a common 'critical thinking' point in environmental science assessments.