Native vs. Non-Native Species: Get Clued In!

Contributed by Cabrillo National Monument Biological Technician Stephanie Glenn

We often hear about introduced or invasive species, but have you ever wondered how biologists know which species are native to an area? How do we know Argentine ants found here in California were originally only in Argentina? Or that the California Condor also inhabited Arizona thousands of years ago? What evidence do scientists use to estimate a species' native range? Although these may seem like simple questions, the process of answering them can be rather complex. Biologist must piece together clues about the species' past in order to determine its native range.

So what does natural or native range mean? Natural or native range refers to the area over which a species is naturally distributed and dispersed.  Physical barriers, such as a mountain range, or biological requirements, such as body temperature, naturally limit the distribution of a species. Sometimes competition with other local species can curb how far a species disperses. What make it so difficult, then, to determine a species' native range? The simplified answer is people. Many species have been artificially dispersed through human mediation, both intentionally and unintentionally. Ancient Maya civilization altered forest flora composition in favor of fruiting plants. European explorers brought exotic livestock to new lands. Colonial American farmers cleared out large areas to plant non-native crops that would flourish and provide food. Even today the transportation of goods and materials for trade can transport biological hitchhikers to new environments. Thus, over thousands of years of anthropogenic migration and alteration, many species have been spread far beyond their native range. Biologists really have their work cut out when trying to determine the origin of a species.

The most common clues biologists use to estimate the native range of an organism are historical records and inventory efforts. Here on Point Loma, we use the descriptions in ship journals of early explorers,’ such as Cabrillo and Vizcaino, to understand what native species may have been here in the 1500 and 1600’s. As early as the 1800s, naturalists began exploring areas all over the world specifically to catalogue the species they encountered, and to assemble vast collections of unique and new species. Examples are Lewis and Clark’s exploration of the northern United States in the early 1800s, and Darwin’s famous expeditions on the Beagle in the 1830s. Alfred Wallace gave thorough accounts of species in the Malay Archipelago during his travels in the 1840s,and John Muir spent much of his life exploring the flora and fauna of Alaska and North America in the 1860s. After the invention of the camera in 1863, photographs became an important clue biologists use to determine species’ historical distributions. The records, photographs, and voucher specimens from these and other pioneers’ travels are stored in natural history museums and archival collections located all over the world.

This type of inventorying still continues today.  Here at Cabrillo, an archival museum of species found on the peninsula and in the surrounding waters is underway. The small mammals, herptofauna (reptiles and one amphibian), marine and terrestrial invertebrates, and fish that we enjoy here today will be identified and documented for future biological research.

Biologists and paleontologists will also look at fossil records for clues about historical species distribution. California Condors nearly went extinct in the early 1980s due to lead poisoning, collision with wires, and shootings. Previously these birds had been sighted in northern Arizona. But it was unclear whether this bird's native range included Arizona and areas of the Grand Canyon or if it had artificially dispersed there with the introduction of cattle ranching. By looking at fossil records, paleontologists were able to confirm its existence in Northern Arizona thousands of years ago and a captive breeding program has successfully released several mating pairs on the Paria Plateau of the Vermillion Cliffs just north of Grand CanyonNational Park.        

In recent years, biologists have started to use genetic analysis for clues about a species' origin. By looking at the genetic structure of the population, biologists can determine if the species has been in the area for a long time. Native populations typically have a large gene pool and high level of diversity in their gene pool. On the other hand, introduced species often have low levels of genetic diversity within the population due to the genetic bottlenecking of the gene pool when a small subset of the native population is relocated in a new environment. Biologists are using genetic clues more and more regularly to determine which species are non-native in areas where little historical information is known. For example, biologists used genetic analysis of cut-throat trout populations in GlacierNational Park to determine which lakes contained native populations.

Often times, biologists need to piece together several of these clues to estimate a species' natural range. And even then much debate and controversy can be had. Many historical and fossil records are incomplete, especially for less conspicuous organisms, such as invertebrates and many plants. Historical records can also be misleading if a species is misidentified and no voucher specimen is preserved. With an estimated 30 million species on Earth, it will take a lot of collecting and cataloguing for archival collections to be complete and accurate. Genetic analysis can also be misleading if an introduced species has been in a new region for a very long time. Thus, biologists make the best estimates of a species' native range given the clues they have.