1. Explain how tolerance limits to environmental factors determine distribution of a highly specialized species such as the saguaro cactus.
Tolerance limits are the minimum and maximum levels of a certain environmental factor in which beyond it a species is not able to survive. For the saguaro cactus, freezing temperatures determines the maximum tolerance limit and determine just how far north this species can be found, because any farther north the caucus would freeze, killing the growing tips of the plant and ending development.
2. Productivity, diversity, complexity, resilience, and structure are exhibited to some extent by all communities and ecosystems. Describe how these characteristics apply to the ecosystem in which you live.
Native plants on Hawaii are primarily responsible for primary productivity as they are the ones converting sunlight into the energy that is eventually cycled up the chain. Diversity happens because of speciation and adaptations of Hawaii species to the environment of the islands. The complexity of the ecosystem comes as a result of millions of years of chance evolution. Resilience and structure develops accordingly in a fully mature ecosystem.
3. Define selective pressure and describe one example that has affected species where you live.
Selective pressure is a form of evolutionary pressure that either reduces or raises reproductive success in a proportion of a population with a certain genetic trait. The different species of Hawaiian honeycreepers all evolved from finches that arrived on the islands several millions of years ago, each now occupying its own ecological niche due to selective pressure. For example, the ʻiʻiwi evolved a long and curved beak adapted to sipping nectar from flowers, while the Palila developed short but strong beak optimized for crushing seed pods.
4. Define keystone species and explain their importance in community structure and function.
A keystone species is one that plays a critically important role in maintaining a biological community out of proportion to its population. They can be a keystone predator, where predation of herbivores keep their numbers in check and prevent the overeating of plants, or fruit-bearing plants that feed primary consumers that in turn form the diet of predators higher up the chain. Their removal from a community would cause a ripple effect that affects all species in that particular ecosystem.
5. The most intense interactions often occur between individuals of the same species. What concept discussed in this chapter can be use to explain this phenomenon?
Competition between individuals of the same species is called intraspecific competition. This is dealt with by either having the young of a new generation disperse to new habitats, territorial behaviors forcing the movement of individuals to new habitats, or by use of resource partitioning for different generations.