 Tudor England had a problem with Europe. King Henry VIII wedged war with France. His daughter Queen Elizabeth fought off the Spanish Armada. They needed wood to build their warships, and they turned to Ireland to get it. An Irish poet in the 16th century wrote the following lament, regretting the loss of these forests and the biodiversity they contained. What shall we do for timber? The last of the woods is done. No sound of ducks or geese here. Hawks cry or eagles call. No humming of the bees here. That brought honey and wax for all. Appreciation of the importance of the earth's biodiversity in sustaining life and inspiring art and literature goes back much further as these cave paintings attest. Our early ancestors also appreciated the fact that the types and abundances of plants and animals that we see around us that they vary from place to place. However, the very first formal quantification of biodiversity happened in 1855 when Charles Darwin identified and counted the plant species growing in the Great Puckland's meadow beside his house in southern England. There are over six times as many people on the planet today as there were when Darwin was studying his meadow. This increase in population growth and the associated economic development has placed huge pressures on the planet. Biodiversity is in crisis and many species are imperiled. To try and understand what's happening as part of this biodiversity crisis, my colleagues and I, as part of my ERC biotime project, compiled data from around the world where ecosystems had been monitored and the types and abundances of plants and animals counted there systematically over a number of years. Our analyses of these data showed that, on average, the numbers of species that we see in the location shown in this slide does not change over time. This might surprise some people. However, the types of species that we see in these places is changing dramatically and the pace of change is much greater than ecological theory predicts. So what is happening? It seems that the combinations of climate change, invasive species and habitat loss are leading to situations where ecosystems are increasingly dominated by the same species. We call this biotic homogenization. Biotic homogenization is something that we see in many parts of the world, including, for example, in the seas to the west of Scotland. Here, the seas have warmed over the past 30 years and, crucially, the water temperatures are now much more uniform throughout the region. In parallel, the types of fish that we see in these regions have also become more uniform. The fish that live in cold waters can no longer thrive in this region. There's a parallel, if you like, in the way the same shopping chains re-dominate shopping malls throughout the world. So should we worry about biodiversity change? Should we care about biotic homogenization? Ireland's history gives us a glimpse of what can happen when ecosystems become more homogenized. In the 1840s, most people in Ireland depended on a single crop, the potato. This crop failed in successive years as a result of potato blight, with nothing else to turn to. Famine and destitution were the inevitable result. By the end of the famine, the population of Ireland had decreased by 25% as a result of death and emigration. I grew up in Ireland, and though I was born over a century after the famine, I was still very conscious of the influence that the famine had on people's attitude towards farming and food. Biotic homogenization is one crisis facing our environment. This increasing dominance of different species, particularly non-native ones, has led to discussions for natural ecosystems and for agricultural ecosystems. It means that they're less resilient in the face of environmental change. Taken together, our work shows that we need to do more than count species. We also need to preserve ecosystem distinctiveness. And to do this, we need to limit the anthropogenic climate change. We need to halt spread of invasive species. We need to protect the environment in ways that allow native species to thrive. We have one earth. It is where we evolved. We depend on its biodiversity to sustain us. Ecology and economics come from the same Greek root, oikos, meaning house and household. So our challenge is to come up with innovative ways to protect the biodiversity and protect ecosystem distinctiveness in this beautiful but fractured planet that is our home.