Habitat and Habitat Selection: Theory, Tests, and Implications

Ancient Nabateans prospered in a green patchwork Negev by harvesting its sparse rainfall with an ingenious system of hillside dykes and catchments. They anchored their commerce with way-stations taxing the long lines of spice-laden camel caravans that, like tall ships, sailed the dunes and barren, rocky landscapes of the Middle East. Even now, flocks of the Negev’s nomadic Bedouin slake their thirst in the Nabatean’s longabandoned, hand-hewn, bedrock cisterns. Modern Negev immigrants see the Nabateans as an inspirational parable for gritty determination, hard work, and invention. The Nabatean desert “experiment” is also a parable for habitat and habitat selection. At their peak, Nabatean cities were inhabited by only a few thousand people. Most of the Negev was too harsh to support even their creative agriculture. In the parlance of ecology, the Nabateans strived to eke out their precarious existence in a landscape containing a few fragile source habitats embedded in an inhospitable sink. As the Nabatean cities grew, so too did their demands on the sources. Wonderfully engineered agriculture was necessity as much as invention. Irrigated land subsidized formerly lush oases. The Nabateans lived on the razor’s edge. Wars, the age of sail, and altered trade-routes sealed their fate. The Nabatean economy collapsed and the Negev returned to the nomads. Similar stories are written large in all human history. The Polynesian migration through the South Pacific is not so much a legacy of heroic adventure and superb naviga tion as it is an escape from poverty and starvation. The great human migrations to North and South America also can be understood as density-dependent dispersal by destitute people leaving lands of hardship in favor of the promise of future prosperity in an under-populated new land. Today’s refugees from famine, war, and persecution swarm the globe in search of a better life. Humans, like all species, require space in which to live. And, like all other species, our abundance varies across space. We disperse our descendants to live in new places.