Last week the remnants of Hurricane Simon passed through Tucson. The city received just an inch of rain, but the story was different up in the mountains. The summit of Mt. Lemmon, rising almost 7000′ above the city, recorded five inches of precipitation in a single day. The reason is orographic lift – mountains force…

One of best known patterns in ecology is the latitudinal gradient in biodiversity. Near the poles there tend to be fewer species than in the tropics. Here are two examples from my own travels. First, a moist lowland forest on the Pacific slope of Costa Rica (9°N latitude). In a hectare of forest you can…