Biodiversity loss proceeds currently on all scales, - from genetic biodiversity of individuals - to a global loss of ecosystems. But the actual loss happens first on a local scale - and then accumulates on others. Some human actions may cause some habitat loss or fragmentation, - which turns the earlier diverse ecosystem into a poorer one.
On a local scale, this means that the number of species, - the so-called species regions, decreases. Often in the degraded ecosystems, - one or two species become notably more abundant than the others. Together, the low species regions and the dominance of a few species - cause decreased alpha diversity, - alpha being the local part of biodiversity.
A classic example of a human degraded system with low local biodiversity - is eucalyptus plantation or an oil palm field. This kind of ecosystem replaces a patch of tropical rainforest, - the local biodiversity decreases heavily. Another scale of biodiversity is the differences between the areas.
This spatial turnover of biodiversity is called beta diversity. Depending on the scale of measurement, - human action may increase or decrease beta diversity. Usually, the increase is temporary.
Our reflection of increased beta diversity - is based on an irrelevant scale of measurement. For example, replacing a rainforest with a tree plantation - may first increase the beta diversity - because it brings new species to the area. For example, some species dependent on open areas may live on the plantation.
However, usually, the beta diversity between two patches of rainforest - is higher than between two patches of a plantation. When the cover of the plantation increase, - at some point, the overall turnover in the landscapes starts to decrease. Together the alpha and beta diversity build up as the global biodiversity, - the so-called gamma diversity.
Considering the long-term effects, this is the most important scale. Because biodiversity is permanently lost when it disappears on the global scale. The global loss of a species is called extinction.
Extinction can't be reversed. When biodiversity loss proceeds in the ecosystems, - their complexity decreases in many ways. One part of the complexity are the species themselves - but also the interactions between the species decrease.
This kind of decreased complexity easily accumulates - because the interactions between some species may maintain - the living conditions in the habitat suitable for many other species. For example, we know that often the top predator hunts a smaller predator - and helps the prey species to survive in the area. If the top predator is moved, - the smaller predators may become so abundant - that they cause the loss of some of the prey species.
Decreased species regions may decrease the resilience of the ecosystems - towards different kinds of natural or human-induced disturbances. For example, a disease may kill all the trees in a forest - if they belong to the same species, - but could not cause notable harm in a natural forest - with high tree species diversity. Similarly, especially hot summer could destroy - the breeding success of some bird or fish species - but most likely not all, if the community is diverse enough.
To summarize, biodiversity loss happens on all scales. Often at the local scale, - the loss does not seem to be very important. One may easily think that the biodiversity is retained elsewhere - and that the lost values are still quite common.
However, the loss of common eventually accumulates - by decreasing the turnover between areas, - decreasing the interactions between the species - and the resilience of the ecosystems. Protecting biodiversity, when it is still common, - is far easier than if the actions are started at the point - when biodiversity features are already rare.
