What is a habitat?
What is a habitat?
by Lisa H. Sideris
In ecology, a habitat designates a species’ natural home and place of abode. A habitat is where an organism’s unique survival needs are met and thus where it “prefers” to be. The language of preference is common in descriptions of the relationship between organisms and habitats, and it suggests, intentionally or otherwise, some degree of agency and choice. Indeed, as a habitat changes over time, its denizens can sometimes adapt and adjust by pivoting to different food sources or seeking out new environs in which to hunt, find mates, or take shelter.
But habit preferences are constrained—sometimes rigidly so. Like millions of humans around the world, many species are now at risk of becoming climate refugees: forced to flee their homes or perish as conditions make life untenable in their historic range.
When their habitats are compromised, some organisms are able to relocate of their own accord. Others need help finding suitable habitat either because they are rooted in place, as with plants and trees, or because their survival needs are highly specific. In a preemptive move, some conservationists and concerned citizen scientists are opting to physically relocate vulnerable species to areas where they stand a better chance of adapting to a changing climate. This practice, often called assisted migration, is not without controversy nor is it always successful. Species might fail to thrive in their new homes, or, conversely, may become so numerous that their presence poses a threat to existing inhabitants. Interventions like these—increasingly common in wildlife conservation—raise philosophical and ethical questions about humans assuming the role of directing the evolutionary trajectory of other species.
Because its habitat needs and those of its host-plant are so particular, the El Segundo blue butterfly (ESB) faces mobility challenges. Dependent upon a single plant at every stage of its development and life cycle, the butterfly is uniquely at home where it lives. Its tiny fragmented habitat is bounded by intensive land development and highly extractive industry while also subject to the usual threats from invasive organisms, weather extremes, disease, and pesticides.
Dune communities where the butterfly and sea cliff buckwheat prefer to live are characterized by changeability and flux. Wind exposure, salty sea spray, and shifting sands continuously reconfigure the landscape. Native flora and fauna learn to thrive in this shifting topography and coast buckwheat is no exception. Humans, by contrast, while irresistibly drawn to the windswept beauty of coastal landscapes and changing ocean tides, seek stable habitats on which to build their homes and supporting infrastructure.
Efforts to secure the ever-shifting coastal bluffs, and thereby satisfy those human preferences, have introduced a variety of additional threats to the butterfly. Invasive plant species, for example, are sometimes recruited to help stabilize the dunes. Chief among these “coastal invaders” is carpobrotus edulis (known as sour fig) and carpobrotus chilensis (sometimes called sea fig). Both plants, which easily hybridize, are colloquially known as ice plant: a South African succulent that blankets highways and coastal dunes with stubbornly thick mats of springy green spikes. These spikes reflect light in ways that appear to sparkle and shimmer like ice crystals. The plant periodically erupts in a riot of delicately fringed, neon-bright flowers in shades of yellow, purple, pink, and orange. Despite its reputation as an invader, the aesthetic qualities of the plant make it difficult to despise altogether, and it is admired by many gardeners.
Thus, like the butterfly whose habitat it threatens, ice plant’s successful invasion of California is tied to innovations in transportation and human desires for speed and mobility—but also stability of a sort. Engineers introduced the plant in the 1900s as “an erosion stabilization tool” along railroad tracks and roadsides. In the 1970s, as car culture was ascendant in California, ice plant began to appear on roadway medians and shoulders as what we might call fast-growing freeway flora. It was prized for its ability to block blowing sand and slow the spread of wildfire and even, on occasion, the motion of a wayward speeding car. Active efforts to curb the spread of ice plant run the entire length of the California coast. College students, school children, and community volunteers are often recruited to remove the plant and restore native species that are critical to dune formation and stability. The laborious work typically involves hand-pulling individual plants or rolling up large mats like carpet. Despite determined efforts to stop its spread, ice plant continues to overrun many of California’s most iconic beaches.
If the ESB is unusually constrained by the size and specificity of its habitat and resource requirements, the land on which it makes its home is defined by the restlessness of humans and our cultures of global mobility. We who value free movement have evolved over time into a species that, for a variety of reasons, transports other creatures to new places as well. Sometimes people bring plants and animals with them to make them feel more at home in new and unfamiliar environments; sometimes transportation happens accidentally, as when organisms hitch a ride, unseen, with human travelers. With the advent of increasingly aggressive conservation practices like assisted migration, endangered and threatened species are also relocated to help them weather the extremes of climate change—itself a byproduct of our energy-intensive hypermobility.
But not all species are able to find new homes as readily as we do. Even those graced with wings and the power of flight, features humans have long admired and emulated, may not seek out new habitats. The El Segundo blue butterfly prefers to stay put.
Masthead image: “Sea cliff buckwheat,” photo by Lisa H. Sideris.
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