a) Beaver-dam buildings → (iii) Pond floods
b) Forest fire → (i) New plants can grow because of an increase in sunlight on the forest floor
c) Lack of rainfall  →  (ii) Zebras migrate farther to find water holes
d) Invasive water plants arrive →  (iv) Sunlight is blocked for native seagrasses
e) Grasshopper outbreaks  →  (v) Crops are wiped out along the prairie
f) Coyote disease decreases the population →  (vi) Mice population explodes
Explanation:
a) Beaver-dam buildings → (iii) Pond floods
This is an example of how some species might produce damages in ecosystems. Beavers are known for their dams, where they hide from predators, find shelter, reproduce, and feed. With time, and as the beaver population grows, these dams get bigger each time. These animals keep cutting down trees and covering some wider areas that were inhabited previously by other species. The landscape changes, these areas get flooded permanently, most vegetation dye, the soil properties get altered, and just a few species can keep living there. The ecosystem changes.
b) Forest fire → (i) New plants can grow because of an increase in sunlight on the forest floor
This is an example of biological succession. Stable forests characterize as having big old trees that compete for light developing big canopies at heights. Poor light reaches the ground and allows some smaller species to grow. When a fire occurs, some of these trees might fall or disappear. These fire events open windows in the forest through which sunlight directly reaches the ground. Many new species can germinate and grow. There occurs a renovation of vegetable species in the forest and the consequent renovation of other living forms. Â
c) Lack of rainfall  →  (ii) Zebras migrate farther to find water holes
It is not unusual that some species need to migrate looking for food or water. In certain areas, seasonal differences are very sharp, and while some periods characterize as producing plenty of food and water, some others characterize as lacking them, dry seasons especially. Animals develop different strategies to face these moments. Zebras need to migrate to find a new source of water to ensure proper hydration.
d) Invasive water plants arrive →  (iv) Sunlight is blocked for native seagrasses
A very known global environmental problem is the damage caused by invasive species. In a few words, exotic species arrive in a new area out of their native distribution range, establish, grow, adapt, and reproduce. These exotic species turn into invasive species when they overgrow, sharply increasing their reproductive rate. At this point, interaction with native species becomes harder, competing for resources such as space, light, food, shelter, water, among many others. Invasive species become such a good competitor that end by displacing native species. In the exposed example, invasive water plants arrive, and their population overgrows. They compete for light with native seagrasses and end by blocking it for them.
e) Grasshopper outbreaks  →  (v) Crops are wiped out along the prairie
This is an example of the prey-predator relationship. In this case, grasshoppers are the predators, and crops are acting as the prey. Whenever one of the population increases in size, the other one follows this increase, causing the decrease of the first one. When the first population decreases, the second one also decreases. In this example, grasshopper outbreaks, meaning an increase in predation rate over crops. Many more individuals are feeding on the crops, causing more damages to the plants´ population. Crops do not have enough time to recover, so they are wiped out.
f) Coyote disease decreases the population →  (vi) Mice population explodes
This is also an example of the prey-predator relationship. In this case, coyotes are the predators, and mice are acting as the prey. As coyotes are affected by the disease, which causes a decrease in their population size, mice seem to be favored, as they are not predated. They have enough time to recover as a population and increase in size. Coyotes´population decreases in size, so there are many fewer individuals feeding on mice, and hence, the mice population increases very fast. It explodes.
