There are two types of cascade:
In top down cascades, as illustrated in Figure 1:
Examples of top down cascades include:
It’s worth noting that these effects can vary over time.
While mid-level consumers might experience an initial population explosion, the resulting over feeding can drive their food sources to extinction, in turn causing their own demise.
In bottom up cascade, as illustrated in Figure 2, the producer population decreases, reducing the energy input into the system. As a result, there is a reduction in the population of all species at higher trophic levels.
Biological systems are complex, and predicting the impact of changing populations is extremely difficult for a number of reasons. Firstly, simple food chains are actually part of complex webs, with many interactions of different strengths, influenced by:
Secondly, population density is also controlled by other factors such as:
Finally, communities are not discrete areas: they merge with those around them.
The precise community level impact of zooplankton grazing on microplastics obviously requires further study, but what is already clear it that human interactions which cause the decline of one population within a community, have a ripple effect that indirectly reduce that community’s biodiversity.