Final answer:
Overcrowding in an environment most commonly leads to a decreased food supply, along with habitat loss, increased pollution, and the effects of climate change, all of which contribute to a decline in biodiversity. Overcrowding can also reduce ecosystem stability and result in poorer air and water quality.
Step-by-step explanation:
The effect of overcrowding in an environment is typically a decreased food supply. As human populations increase, there is a higher demand for land, which often leads to habitat destruction. This habitat loss, along with increased pollution and the effects of climate change, can lead to a decline in biodiversity. Overcrowding can also lead to the overharvesting of resources and the introduction of non-native species, both of which are detrimental to the original ecosystems. Additionally, as overcrowding puts more pressure on an ecosystem, the stability of the ecosystem is likely to be compromised, and this can result in reduced air and water quality.
Contrary to some of the incorrect options provided, biodiversity tends to decline as human populations increase because the increased use of land for agriculture, urban development, and industry leads to the displacement and reduction of many species. This is further exacerbated by global climate change, a consequence of the increased energy needs of growing populations and the associated greenhouse gas emissions from the use of fossil fuels. However, it is worth noting that in complex ecosystems, biodiversity supports the resiliency and functionality of the ecosystem. Yet, as human populations grow and their impacts intensify, biodiversity is more likely to decrease.