11.3 - EXERCISES

Populations have certain attributes that cannot be observed in individual organisms. For instance, populations exhibit characteristics like population density (how many individuals live in a certain area), birth and death rates, and patterns of distribution. These attributes provide insights into the health, growth, and sustainability of a population as a whole, while individual attributes such as height or weight are traits that only pertain to single organisms.

The intrinsic rate of increase, r, can be determined using the formula for exponential growth. If a population doubles in size in a given time period, we can use the formula N = N0e^(rt), where N0 is the initial population size, N is the final population size, and t is the time in years. For a population that doubles in 3 years, we can simplify to find r, which would involve logarithmic calculations.

Plants have developed several defense mechanisms to protect themselves from herbivores (animals that eat plants). These defenses can be physical, such as thorns, tough leaves, or spines, or chemical, such as producing toxins or unpleasant tastes that deter herbivores. Some plants also exhibit growth patterns that minimize damage, like growing low to the ground or producing leaves that are hard to digest.

The interaction between the orchid and the mango tree is known as epiphytism. In this relationship, the orchid grows on the mango tree but does not harm it. This is a type of commensalism, where one organism benefits (the orchid receives support and access to sunlight while being up high) and the other is neither helped nor harmed (the mango tree is not affected).

Biological control involves the use of natural predators or parasites to manage pest populations. The ecological principle behind this is that every ecosystem has complex interactions between species. By introducing a natural enemy to the ecosystem, you can lower the pest population without relying on chemical pesticides, promoting a healthier balance in the ecosystem.

A population refers to a group of individuals of the same species living in a particular area at the same time, while a community includes all the populations of different species that interact in a certain environment. The concept of a population emphasizes individual species, whereas the concept of a community highlights the interactions between different species.

These terms describe different types of relationships in ecology:
(a) Commensalism - one species benefits while the other is unaffected. Example: barnacles on whales.
(b) Parasitism - one species benefits at the other's expense. Example: ticks on mammals.
(c) Camouflage - a survival strategy that allows an organism to avoid detection. Example: a chameleon changing color to blend into its background.
(d) Mutualism - both species benefit. Example: bees pollinating flowers.
(e) Interspecific competition - competition between different species for resources. Example: different bird species competing for nesting sites.

The logistic population growth curve illustrates how populations grow rapidly initially, but as resources become limited, the growth rate slows down and stabilizes as it reaches the carrying capacity of the environment. This curve has three phases: exponential growth, deceleration as resources are consumed, and stabilization when the population levels off at the environment's capacity.

The correct choice is (d). Parasitism is a relationship where one organism (the parasite) benefits at the expense of the host organism. The host suffers as the parasite feeds off it, which can lead to health issues or even death for the host. This relationship showcases the balance in ecosystems where interactions between species can greatly influence their survival.

Three important characteristics of a population include:
1. Size: Indicates how many individuals are present in that population. Size can affect reproduction rates and extinction risk.
2. Density: Refers to how many individuals live in a given area, impacting competition for resources.
3. Distribution: Describes how individuals are spaced in their environment, which can be random, clumped, or uniform. This affects mating success and resource availability.