Understanding Species Roles and Population Dynamics

Species Roles in Communities

Niche and Species Roles

A species' niche defines its way of life within a community, including its role and interactions. Species roles can be categorized as:

• Generalist: Tolerates a wide range of conditions and resources.
• Specialist: Has a narrow range of tolerance, specific food and habitat requirements, and low reproductive rates.

Specific Roles

• Native Species: Originate in a particular area.
• Non-native Species: Introduced to an area, either accidentally or intentionally.
• Indicator Species: Sensitive to environmental changes, serving as a biological "smoke alarm."
• Keystone Species: Play a critical role, influencing the types and abundance of other species (e.g., pollinators, top predators).
• Foundation Species: Create or enhance their community, often acting as scavengers.

Species Interactions

• Interspecific Competition: Two or more species compete for limited resources, often resolved through resource partitioning.
• Predation: Predator-prey relationship.
• Parasitism: One species benefits at the expense of another, potentially causing illness.
• Mutualism: Both species benefit (e.g., food and protection).
• Commensalism: One species benefits, while the other is neither harmed nor helped.

Ecological Succession

Ecological succession refers to the changes in communities over time. Two types of succession exist:

• Primary Succession: Begins with bare rock, no vegetation, and no soil. Plants gradually colonize the area.
• Secondary Succession: Starts with existing plant life or soil (e.g., growth on disturbed land).

Population Dynamics

Population Change

Populations can grow, shrink, or remain stable. Four factors influence population change:

• Birth rate
• Death rate
• Immigration
• Emigration

Carrying Capacity

Carrying capacity is the maximum population size a habitat can sustainably support. Exceeding carrying capacity can lead to:

• Population crash and stabilization
• Population crash and extinction

Humans have increased carrying capacity through technological advancements, energy use, disease control, increased food production, and extended lifespans.

Key Population Factors

• Fertility Rate: Number of children born to a woman during her lifetime.
• Replacement Fertility Rate: Average number of children a couple must have to replace themselves (approximately 2 children per couple).
• Life Expectancy: Expected number of years of life.
• Infant Mortality: Death rate of children under one year old.
• Demographic Transition: Population changes that occur as a country develops.