Question

Species that have many offspring at one time are usually: a. $r$ -selected b. K-selected c. both $r$ - and $K$ -selected d. not selected

Short answer

Species that have many offspring at one time are usually $r$-selected.

Step-by-step solution

Understand $r$-selected species

$r$-selected species are those that emphasize a high growth rate and typically produce many offspring at once. They reproduce early and have a short lifespan. Examples of $r$-selected species include insects, rodents, and weeds.

Understand $K$-selected species

$K$-selected species are those that emphasize efficiency in resource use and typically produce fewer offspring, investing more time and energy in their care. They reproduce later in life and have a longer lifespan. Examples of $K$-selected species include elephants, humans, and whales.

Analyze the options

a. $r$-selected species are known for having many offspring at once. b. $K$-selected species usually produce fewer offspring that require more care. c. Both $r$- and $K$-selected species cannot be correct, as these are two opposing strategies. d. Not selected is not a valid option, as all species employ one of these strategies.

Choose the correct answer

Based on our analysis, the correct answer is: a. $r$ -selected

Key concepts

Reproductive Strategies

Understanding the reproductive strategies of different species is key to grasping their survival mechanisms. Reproductive strategies are adaptive mechanisms that organisms have evolved to ensure their genes are passed on to future generations. These strategies can be broadly categorized into r-selected and K-selected species.

For r-selected species, the reproductive strategy is quantity over quality. Think of rodents or insects, which may have hundreds of offspring, but with less parental investment in each. They mature quickly, reproduce at an earlier age, and are often adapted for environments where resources are unpredictable and competition is low.

In contrast, K-selected species emphasize the quality of their offspring. Elephants and humans are prime examples, producing fewer young but investing significant resources and care into each one. This strategy is typical in stable environments where competition for resources is higher, and the focus is on survival and maintenance of the population. To internalize these concepts, visualize an insect laying hundreds of eggs versus a human mother nurturing her child for years.

• r-selected species produce many offspring with less investment per offspring.
• K-selected species produce few offspring with significant investment per offspring.

Species Life-History

Species life-history encompasses the stages of an organism's life — from birth through reproduction to death — and the adaptations they use to survive and reproduce. This includes the lifespan, age at first reproduction, and the number and care of offspring.

The life-history strategy a species adopts is shaped by evolutionary pressures and dictates how resources are allocated to growth, reproduction, and survival. r-selected species often have a 'live fast, die young' approach, allocating most of their energy into rapid growth and early reproduction. For them, it's a race against time and they take the bet of having numerous offspring hoping that some will survive in the unpredictable environment.

K-selected species, on the other hand, take a 'slow and steady' approach. They grow more slowly, reproduce later in life, and invest heavily in a few offspring, enhancing their survival chances in competitive environments.

• Lifespan, growth rates, and reproductive efforts define a species' life-history strategy.
• r-selected species have a fast life-history strategy; K-selected species have a slower, more deliberate strategy.

Population Ecology

Population ecology is the study of how populations of species interact with their environments and change over time. It focuses on factors such as birth rates, death rates, and the dynamics of population growth.

R-selection and K-selection are important concepts in population ecology because they directly influence these factors. An r-selected species, which produces many offspring, can experience rapid population growth when conditions are favorable but may also suffer steep declines when conditions worsen. Think of a weedy plant that quickly covers an area after a disturbance but may die off as quickly when faced with drought.

K-selected species, with their stable and regulated population growth, often dominate the mature phases of ecosystem development where they compete effectively for limited resources. Their populations tend to be closer to the carrying capacity (K) of their environment, which is the maximum population size that the environment can sustain indefinitely.

• Population ecology examines the birth, death, and growth rates within a population.
• r-selected and K-selected strategies influence how populations respond to environmental changes and resource availability.