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Are We in the Sixth Mass Extinction?

Read time: 5 mins

Are plants intelligent? It would seem so, judging by the program of the new edition of “Evolution Day”, dedicated to the marvelous world of plants and their "intelligence" (Milan, Museum of Natural History, February 10-12th.Scienzainrete will perform the live streaming of the event). In the international panel of speakers stands the Finn Ilkka Hasski, probably the greatest living ecologist (winner of Balzan Prize 2011, and of the Crafoord Prize). Its fame is mainly due to his twenty-year studies on the butterfly Melitaea cinxia in the Åland Islands of Finland, with whom he was able to show several interesting things: like the fact that the land use and habitat fragmentation, typical of our advanced societies, are the main causes of the reduction of plant and animal biodiversity. And how, among other things, the loss of biodiversity is also impacting on our health. We interviewed him for Scienzainrete.

This year's edition of EVOLUTION DAY is titled "The intelligence of plants." According to you, in what sense we can say that plants are intelligent?

We humans tend to define intelligence in such a manner that there is a big difference between us and other animals, to say nothing about us and the plants. However, there are opinions that all living organisms have their own type of consciousness and intelligence. In any case it is apparent that all living organisms, being the product of evolution, are 'intelligent' in the sense that they are well adapted to their own living conditions. 

In your lecture you will speak of mass extinction and biodiversity. Are we on the verge of a new mass extinction?

The mass extinctions of the past are usually defined as periods of time during which more than half of species went extinct. It is not straightforward to compare the past mass extinctions with our time, because the length of the time periods are different. The fifth mass extinction was initiated instantly by the collision of a huge meteorite with Earth, but the full consequences of that collision probably became apparent during a long period of time. Arguably, the human-caused 6th mass extinction started some tens of thousands of years with the demise of the megafauna on several continents, and the rate of extinctions has continuously accelerated to the present time, and is still increasing. Many groups of plants are greatly affected and in fact the extinction rate in plants may be even higher than in animals.

Can you give us an idea of the size of this sixth mass extinction?

The present rate of species extinctions is around 1% of species going extinct in 100 years, but this rate is very likely to increase to at least 10-20% towards the end of this century, and may become even much higher if the rate of desctrution of tropical forests and coral reefs continues with the present rate. 

What kind of risks the man runs as a result of this phenomenon? Can you make some examples?

I think we all agree that, ultimately, our own well-being is entirely based on the environment: clean water, clean air, fertile soils, sufficient food. Loss of biodiversity is a warning signal, indicating a deterioration of the environment. One of the biggest risk is that if we don't pay attention to these warning signals, it may be too late to reverse the cause of environmental changes when the consequences become apparent to everybody. In other words, there are critical 'tipping points' in the state of the environment - if you go beyond that point, a permanent change will happen. I will talk in my presentation about extinction thresholds in the occurrence of species in relation to habitat loss. Climate change is predicted to involve such tipping points, for which reason  the goal has been set to limit climate warming to less than 2 C increase in global average temperature.

There are also other possible consequences of biodiversity loss to humans. In my talk, I will discuss the hypothesis that reduced contact of people with environmental features and biodiversity is a contributing factor to another global megatrend, the rapidly increasing prevalence of allergies and other chronic inflammatory diseases especially among urban populations.

In your theory, extinction of plants and animals depends on several factors, including pollution, climate change, the invasion of alien species and habitat fragmentation. What are the main drivers? And how to determine the extinctions?

So far, the main drivers of extinction have been human land use, which leads to habitat loss and fragmentation to most other animals, invasive species and overharvesting, the latter especially in oceans and freshwater ecosystems. In the future,  climate change will become perhaps the biggest driver, especially in interaction with habitat loss and fragmentation. Extinctions can be predicted based on changes in the abundance and distribution of species that can be predicted based on projected changes in the amount of habitat, climate, exploitation, and so forth. The extinction threat is quantified both nationally and globally, for many groups of animals and plants, using the set of criteria defined by the International Union for Conservation of Nature. Making such assessments of course requires sufficient knowledge of the species. Unfortuantely, for many less well known groups of species such assessments are not possible due to insufficient knowledge.

You have received many awards for his work on the so-called "meta-population" and "ecological debt", which means - if I understand correctly - that species survive for some time after they have been affected by a profound alteration of their habitats. What impact do these concepts have on the natural dynamics? What lessons can be drawn from these theories in the field of conservation and restoration of ecosystems?

Following environmental change, it typically takes a shorter or a longer period of time before the populations have fully responsed to the changes. Because of extinction debt, we are likely to underestimate the threat of environmental changes, because we don't see the full consequences immediately. For this reason, it is very important to be aware of the phenomenon of extinction debt. On the other hand, similar time delays are expected to occur following habitat restoration - we should not become discouraged if the populations don't recover immediately.

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