Threat to biodiversity (about butterfly, polar bears and Brad Pitt);

Everyone care about the environment and enjoy a sunny day walk through the woods (apart for certain categories of people like hardcore gamers), yet these nice places and their biodiversity are threatened partly due to human actions partly to other factors. My mother recently asked me ‘Why is there less bees?’ my answer was (as a true scientific) ‘Well it’s complex’. This post will try to explain some of this complexity by listing the different factors that threaten biodiversity nowadays.

The Range above all things,

Every species in the world have a specific geographic range, lions are in Africa, panda in China and American in America. This specific place where they live happily ever after (until Bob the hunter comes along) is called in biological terms: ‘habitat’, many things will shape the species habitat, like the food that we will found there, the climatic conditions, the shape of the habitat (obviously a dolphins will not be found on land), the presence of other species, the historic background and so on.

This habitat will then define the species range, the amount of square kilometres (or miles for the irreducible from the other side of the atlantic) where a certain species is found.

The range of a species is critical for its survival, because of several reasons:

-bigger range size can contain more individuals and the more you are the less likely you are to go extinct due to demographic reasons (you produce more offspring), stochastic reasons (if an unpredictable event occur there is more chance that some will survive) and genetic reasons (if you only mate with closely related individuals because you are few then genetic diseases are very likely to happen).

-bigger range size are less likely to be severely impacted by extreme weather event (if you are all in one island and this island gets flooded you are on the extinct list)

The issue is that humans have been dramatically reducing species habitat over the past century through pure habitat destruction (to put fields, cities, to get resources like gold or oil), pollution or change in species composition.

So the species are confronted to a degradation of their habitat and therefore they have less and less areas when they can live happily ever after (until John the builder decide to build a new airport), so their range decrease.

As a result species populations are dropping and are much more likely to become extinct.

Another important changes in species distribution is fragmentation, this is when a species previously occurred in big areas (forest for example) that have now been cut down into smaller area.

Habitat fragmentation is everywhere nowadays, when we build a road through a meadow it is separating an original habitat into two patches and small species are particularly affected by this (just count the number of dead animals on highways).

So to sum up this part, every species have a precise preferred habitat where it can live and love (and make babies), this define their geographic range size in this case the size count and the bigger the better. Yet humans are transforming the land around them by building cities, fields … and so this range size is shrinking and push the species closer and closer to extinction. In more scientific terms this is called land-use changed and is the number one reason for biodiversity loss.

(See )

 Climate Change

The climate of the earth is changing, even if some humans might enjoy warmer climate like cold-hating people or ice cream sellers, this change affect all species and in many cases (not all) negatively affect them.

As always in Biology there is not one simple effect but many inter-related ways how climate change can affect a species:

-Each species have a range of climatic conditions under which they can live and reproduce, when we change this they have to adapt or die (sorry for the polar bears they were so cute). Even if this is the most straightforward effect of climate change that we can think of very few study have found that species got extinct due to temperature or precipitation change.

-Climate change can alter the resources of a species by changing their distribution (if the food you are used to eat is no longer where you are you have problems), quantity (less food mean less individuals can live with it), and temporal mismatch (if the resource you eat reach its peak when your children are not yet born then it will be harder to raise them)

-With climate change extreme events such as fire may become more frequent altering species habitat.

A specie can adapt itself to changes yet the speed and magnitude of change is critical to adaptation, the anthropogenic changes to the climate are faster than what was previously experienced.

So by changing the climatic conditions humans are impacting species survival and reproductive rate which in turns affect their chance to survive.

(See a very recent and accessible review)

Species Invasion

Due to climate change and to human, voluntary or not, introduction, new species are invading habitat where they didn’t historically occurred. Like parrots in middle Germany (true story). For example if a certain region gets warmer then certain species that were not able to survive and reproduce in these areas might do so and hence establish themselves there. Or it can be that people after having bought a very nice and exotic snake got fed up of it and decide to release it in the wild , yet this snake species was not present here before, if it can survive and find mates then it will be an alien introduced species. These newly introduced species might have no visible effect at all and might not severely impact the ecosystems, yet in some cases they can lead to dramatic changes in species composition in certain places, through several process: predation pressure (a cat that eats flightless birds), competition over resources (if your food is in limited amount and a goat eats it all) or other…

As a result of this populations can be wiped out from certain places increasing the risk of the species as a whole to go extinct.

(See a nice platform from the UN)

Unsustainable use

We like to eat or collect certain plants or animals coming from the wild (not raised and bred in captivity), examples include most fishes, exotic plants or birds.

When we take away from a population individuals then this population will have to survive without it. If to much are removed then the population will risk extinction. Another aspect of this is that in many cases we are no collecting individuals at ransom but rather taking some particular classes: the bigger, the ones with the brightest feathers or the ones with the beautifulest colours… However these individuals might have the highest reproductive output and thus be the one responsible for most of the population growth. So removing these Brad Pitt’s increase the risk of extinction.

(See or


Pollution is legally defined as “The discharge of a toxic or contaminating substance that is likely to have an adverse effect on the natural environment or life. “

These substance affect ecosystems and species and can have harmful effect on them ranging from lowered reproductive output to death. The first and most direct effect is when an animal eat a substance and died from it (like sea turtle eating plasitc bags). Second a process called biomagnification can occur in food chains where small creatures like planctons are ingesting substances that are not deadly to them and then their predators (like fish) eat a hundred of them still the concentration of this substance is still not high enough to cause death but at an higher trophic level (like birds) these substances become so concentrated that it causes the death of many individuals (example are lakes contaminated in the US by PCB killing birds). Our industry release in the atmosphere substances like sulfure dioxide and nitrogen oxide and these cause acid rain that lowered the ph of the soil affecting plants and whole ecosystems that depend on them (example are the taïga forest in russia). Third intensive agriculture recquires fertilizers that are drained by the rain into rivers, lakes, seas and change the nitrogen concentration in these habitat that were adapted to other conditions, this is called eutrophication and it can radically change the species composition and biodiversity of these habitat in many cases green alguae are supressing any other plant species in the detriment of all species depending on them, extreme cases happen in so-called death zone were so many plants develop that micro organisms living on them consume all the oxygen in the upper layer of the water leading to complete oxygen depletion in the deeper zones were barely nothing is left. So called red tides produced by dinoflagellates also come from eutrophication.

Fourth part of the carbon dioxid that we are releasing in the atmosphere ends in the seas changing its ph and threatening complex equilibrium of chemical reactions from which depend many shell building mollusc and corals.

(See for acid rain, and )

To wrap everything up, we humans really like butterfly and singing birds but we threaten all these species by changing their habitat, changing the climate, putting new species where they live, taking out all Brad Pitt and Keanu Reeves from their male stock and by adding harmful chemicals in their environment.

As always these problems need to be tackled together and not separately, every one of us can do little efforts (like stoping eating endangered fish species) to save butterfly, singing birds and creepy spiders (yes they also need to be protected).

(For all this post see the Global Biodiversity Outlook 3 page 55 that also resume the main threat to biodiversity)

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