a) The milkweed is the primary producer in the ecosystem. It manufactures food from the abiotic factors in the soil such as nitrates and water and those in the atmosphere such as carbon-dioxide and sunlight. The milk weed is then fed on by the caterpillar and a primary consumer. The caterpillar is then fed on the mocking bird (secondary consumer)
b) Increased human population growth and their activities have resulted in the emission of carbon dioxide and other greenhouse gases in the atmosphere. This has increased the global temperature. This increase of global temperature increase ocean temperatures causing coral bleaching.
Another example is depletion of water sources by human activities hence causing drought. Drought reduces the amount of vegetation growth due to scarcity of water in the soil (due to lowering of the water table) for plant growth.