Chapter 8 by Andrea Guinanzaca

In chapter 8, Kolbert goes to Peru and meets with a scientist named Miles Silman. Silman is a professor at Wake Forest University and majored in forest ecology, and studies the tropical ecosystems of South America. A question often brought up in this chapter was “Why are tropical climates so conducive to biodiversity?” There’s a theory in tropical areas,  that animals reproduce faster which lead to more genetic mutations. This eventually will cause more varieties of species to develop. Another theory argues that there’s more biodiversity in tropical climates because they have relatively low-temperature fluctuation.  Therefore, there are different zones that can only harbor life with very specific thermal tolerances. As a result, the theory predicts that different animals self-stratify based on the temperatures they can withstand.

Every year, Schefflera trees die off, and every year, their replacements show up at a higher altitude, reflecting the overall changing temperatures of the forests. But also, the increase of snow triggers global carbon dioxide levels to decrease, this causes l a significant drop in temperature. In this chapter, we learn that during the Pleistocene period, the planet became significantly cooler. Silman takes Kolbert on several expeditions to observe the tree plots and together they gather samples. In ecology, there’s a familiar rule that the greater the size of an area, the more species are likely to live there. There appears to be a strong positive correlation between the two variables, such that the number of species in a region is directly proportional to the square root of the region’s total area. This law is helpful in understanding the impact of humanity on biodiversity. Humans decrease the amount of land available for species to inhabit, and therefore decrease the total number of species, too. Due to this, scientists have estimated that between 30 and 50 percent of the world’s species will disappear by the year 2050. Several years ago, National Geographic published a story repeating the conclusion that half of the world’s species could die out by 2050.  There, Kolbert is surprised to find a group of different birds, including tanagers and cock-of-the-rocks. In conclusion, Silman arguing that the changes facing the world’s life forms in the next fifty years will be “apocalyptic”. Therefore, the argument is brought up again… “are human actions causing the Earth to have another mass extinction?”