Functional extinction is the extinction of a species or other taxon such that:Circumstances are changing very rapidly so that this definition may need modification. The notion of "tipping point" seems like a reasonable way of accepting the functional extinction of a species. Once this point of no return is reached and passed the game is over no matter how many individuals are still around. Read on below and we can explore this idea in the modern context.
it disappears from the fossil record, or historic reports of its existence cease;
the reduced population no longer plays a significant role in ecosystem function; or
the population is no longer viable. There are no individuals able to reproduce, or the small population of breeding individuals will not be able to sustain itself due to inbreeding depression and genetic drift, which leads to a loss of fitness.
In plant populations, self-incompatibility mechanisms may cause related plant specimens to be incompatible, which may lead to functional extinction if an entire population becomes self-incompatible. This does not occur in larger populations.
In polygynous populations, where only a few males leave offspring, there is a much smaller reproducing population than if all viable males were considered. Furthermore, the successful males act as a genetic bottleneck, leading to more rapid genetic drift or inbreeding problems in small populations.
THE EXTINCTION CRISIS has this to say:
Clearly this study sees us in the middle of mass extinctions and from that point of view far more species are functionally extinct at the moment than we recognize. In this report, Transitions and Tipping Points in Complex Environmental Systems we see this
It’s frightening but true: Our planet is now in the midst of its sixth mass extinction of plants and animals — the sixth wave of extinctions in the past half-billion years. We’re currently experiencing the worst spate of species die-offs since the loss of the dinosaurs 65 million years ago. Although extinction is a natural phenomenon, it occurs at a natural “background” rate of about one to five species per year. Scientists estimate we’re now losing species at 1,000 to 10,000 times the background rate, with literally dozens going extinct every day . It could be a scary future indeed, with as many as 30 to 50 percent of all species possibly heading toward extinction by mid-century "
CHALLENGE: INCREASING STRESS ON THE PLANET
The world is at a crossroads. The global footprint of humans is such that we are
stressing natural and social systems beyond their capacities. We must address these
complex environmental challenges and mitigate global scale environmental change
or accept likely all-pervasive disruptions. Rapid development and growth of human
populations are causing changes to natural ecosystems and biodiversity loss of a
magnitude and scale not seen before during human existence. Environmental challenges
are increasingly of a global scale; while many changes appear small individually in aggregate they have large and even synergistic effects. At the same time technological advances are changing lifestyle and social norms on every level as well as livelihood patterns. As these socioeconomic systems have become more globally connected and interdependent so too have their interactions with environmental systems. These changes in environmental and social systems represent serious threats to our
economy, security, and human health.
Here is the point in a nutshell:
CHALLENGE: LITTLE TIME TO ACTI suggest that it is worse than that. It seems reasonable from the discussion above that we as a species may reach a tipping point where we may have passed the point of no return. It seems ugly to say it, but if we are not becoming functionally extinct as organisms, we may be as a social system. The latter idea has a double meaning for if we fail to act in time the extinction will be forced on us. What is a bit more subtle is that if we are to prevent this we must also change the social systems we are in. Either way we might say that at this very moment our social systems are functionally extinct.
The rate of environmental change is outpacing the ability of institutions and governments to respond effectively. Issues that previously were addressed at the local level are no longer adequately understood without a regional, continental and, increasingly, global perspective. While we recognize the direct connection between local human activities and global environmental changes, the feedbacks of that
change on regional ecological and social systems are poorly understood. The issue is not just spatial scaling; there is also the temporal disconnect between environmental changes and the human actions that cause them and the policies designed
to address them. We must rapidly increase our ability to forecast change in globally connected natural and human systems, or find ourselves responding increasingly to crises.