Final answer:
An overall decreased density can refer to the decline in population density due to density-independent factors like soil erosion or density-dependent factors such as inbreeding and reduced cooperative behaviors. In ecology, factors impacting population density can lead to an Allee effect in small populations or increased competition in larger ones.
Step-by-step explanation:
When discussing an overall decreased density in the context of ecology and environmental science, it refers to a situation where the population density decreases. This decrease can be caused by a variety of factors such as habitat loss, pollution, climate change, or overexploitation of resources. A specific factor that can lead to decreased density is the practice of plowing fields in straight lines without regard to topography, which can result in increased soil erosion and water loss. This is a density-independent factor because such environmental degradation occurs regardless of the population density and can have the same impact on sparse or dense populations. In the context of population dynamics, an observed decrease in population density could be due to density-dependent factors, such as inbreeding depression, reduced cooperative behaviors, and lower mate availability, which are more pronounced in smaller populations. These effects can lead to a positive feedback loop called an Allee effect, where reduced population density actually leads to a further decline in density. However, at higher densities around the carrying capacity, the negative effects associated with high density, such as competition for resources and increased predation, will usually dominate. An example of density-dependent versus density-independent factors is illustrated by the influence of population density on the rate of population change, where factors like disease spread more quickly in denser populations (density-dependent), whereas natural disasters can affect populations regardless of their density (density-independent).