Invasive? Exotic? What's the difference?

 Posted by at 2:50 pm on May 28, 2010
May 282010
 

The introduction and proliferation of species outside their historical ranges is recognized as a major threat to biological diversity. The problem of “invasive species” has become well known outside the scientific community, although many people are hard-pressed to identify even the most conspicuous invasive species in their area. For example, most people I talk to while I’m doing my research here in South Florida are surprised to learn that the brown anole (Anolis sagrei) – easily the most common lizard in developed areas of Florida – isn’t native here, but an invasive species from Cuba.

The invasive brown anole (Anolis sagrei). This male has been marked with a white paint pen for my research

But not every species that arrives in a new habitat is “invasive,” and a plethora of terms are used, often casually, to describe species living outside their native range. All of these terms, and the imprecision with which they are often used, can confuse scientists and non-scientists alike. Here are a few of the most common: invasive, exotic, non-native, non-indigenous, introduced, established, and naturalized. And let’s not even get into the more emotionally loaded terms like “weedy,” “nuisance,” and “noxious.” What is the scientific consensus on these terms? Well, it turns out that the scientific community hasn’t quite settled on good definitions for all of them, but I’ll do my best to make some basic distinctions between them.

Exotic, non-native, and non-indigenous refer to species occurring outside their historical ranges. These terms don’t necessarily imply that these species have self-sustaining populations in their new range, only that they occur there. Introduced has a similar meaning, but with the added connotation of an anthropogenic (human-caused) colonization event. Established and naturalized describe species that have reached stable, sustainable population sizes in their new range – these species don’t require periodic or continuous replenishment to perpetuate themselves.

A male green anole (Anolis carolinensis), native to South Florida, displays its pink dewlap.

Invasive is the trickiest term. Some use it interchangeably with “exotic,” but this definition is too broad. Most scientists agree that the term invasive should be reserved for those species that have become established not only in human-altered habitats (like urban and suburban environments), but also in less disturbed natural habitats. Some authors also require that to be invasive, a species must have some negative effect on natural habitats. Most non-native species, however, have not been studied well enough to determine whether they have negative impacts on native plants and animals.

In South Florida, exotic and invasive species are everywhere. The brown anole that I study is certainly an invasive by any definition – since becoming established in peninsular Florida in the 1940s, it has spread throughout the state and beyond, it occurs in most habitats, and it competes with the native green anole (A. carolinensis), which seems to be suffering from the interaction.

A pair of red-masked parakeets (Aratinga erythrogenys) at the entrance to their nest hole. This species, while established in South Florida, is not 'invasive' in the strict sense.

On the other hand, there are many South Florida exotics that don’t seem to be invasive yet, and may never be. Last week I photographed a beautiful pair of red-masked parakeets (Aratinga erythrogenys) at a nest hole in South Miami. These parrots are native to Ecuador and Peru, and almost certainly arrived in Miami through the pet trade. They have been established in Miami since the early 1980s, and their populations seem to be self-sustaining if not growing. Their distribution is limited to suburban areas, however, where they often visit fruit trees and bird feeders for sustenance. They have not spread into undisturbed habitats, and they don’t seem to be a threat to native species (although they may compete for nest holes with native cavity-nesting birds). So we could call them a “non-invasive exotic.”

It’s important, I think, to recognize that not all non-native species are invasive. Unfortunately, however, we just don’t know enough about most exotics to classify them as “invasive,” “potentially invasive,” or “non-invasive.” Since most of these species initially become established in human-dominated areas, non-scientists have an important role to play in monitoring the arrival and spread of new species, as well as the interactions between these new arrivals and native species.

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Anoles of Miami

 Posted by at 2:00 pm on May 20, 2010
May 202010
 

I talk a lot about anoles in this blog, especially the species found in Florida. A few weeks ago I posted some pictures and commentary on the anoles of Puerto Rico, but I haven’t had a chance to show you the impressive diversity of anoles that live in South Florida. There is only one native anole in the continental United States, but at least eight other species have become established at various sites in Florida. Four of these exotic species are common at my South Miami field sites.

Male green anole (Anolis carolinensis). Photographed at Matheson Hammock Park, South Miami, FL.

The green anole (Anolis carolinensis) is our only native anole. Many Floridians call this little lizard a “chameleon,” because it can change color; it is most often a brilliant green, but can change between various shades of green, yellow, and brown based on a variety of factors, including ambient light, temperature, and social interactions. Anoles are only distantly related to true chameleons, however, which are members of the exclusively Old World family Chameleonidae. The green anole’s closest relatives live in Cuba, and their colonization of North America is thought to have occurred before the Pleistocene, as A. carolinensis are present in the Pleistocene fossil record.

A. porcatus, a Cuban “trunk-crown” ecomorph (Remember the ecomorph story? You can refresh your memory by reading this post), is probably the closest relative of the green anole, and A. porcatus has been introduced to South Florida. Its distribution is not well understood, however, because it is virtually impossible to distinguish one species from the other. It’s quite possible that I’ve seen A. porcatus at my field sites, but I don’t think I’d know it if I had!

Male brown anole (Anolis sagrei) performing dewlap display. Photographed at Matheson Hammock Park, South Miami, FL.

The most ubiquitous non-native anole in Florida is the brown anole, A. sagrei. A Cuban immigrant, the brown anole was first documented in the Florida Keys in the 1880s, and was established on the Florida mainland by the 1940s. Since then, it has spread rapidly throughout Florida and into other southeastern states. The brown anole is a “trunk-ground” anole, and it fares quite well in marginal or disturbed habitat, like suburban neighborhoods and roadsides. Many Florida residents say that the native green anole has gotten less common since the arrival and spread of the brown anole.

Male crested anole (Anolis cristatellus). Photographed at Matheson Hammock Park, South Miami, FL.

Another “trunk-ground” anole introduced in Miami is the crested anole, A. cristatellus, a native of Puerto Rico. I focus on the brown anole and crested anole in my research, because they are the only common members of the South Miami anole fauna that belong to the same ecomorph. The crested anole was introduced to the Miami area in the 1970s (in fact, there were two independent introductions, one on Key Biscayne and one in South Miami). Unlike the brown anole, however, the crested anole has not spread far from its introduction sites. Along with , who studies the habitat use and thermal ecology of these species, I’m interested in the interactions between these two trunk-ground anoles, and how these interactions influence their respective distributions in Florida.

Male bark anole (Anolis distichus) performing dewlap display. Photographed at Matheson Hammock Park, South Miami, FL.

Two other common anoles are found at my field sites: the bark anole (A. distichus), a “trunk” anole from Hispaniola and the Bahamas, and the knight anole (A. equestris), a “crown giant” from Cuba. The bark anole spends most of its time on the trunks of large trees, where its finely speckled pattern and somewhat flattened shape help it to blend in with its surroundings. The knight anole is quite different from the other four species I have found at my field sites; as the ecomorph name “crown giant” suggests, it is huge (the biggest males I’ve seen are easily 18 inches long, including the tail). The knight anole also readily eats the other anole species if given the opportunity.

Knight anole (Anolis equestris). Photographed at Matheson Hammock Park, South Miami, FL.

Predation by knight anoles aside, the remaining four species interact in many ways. Each species may eat the offspring of the other species (ecologists call this “intraguild predation”). There’s some evidence that the brown anole has a particular propensity for eating the young of other species, which may partly explain why it has displaced the native green anole in some areas. The anoles probably also compete for common resources, like food and perch sites. Ecologists often divide competitive interactions into two classes: exploitative competition and interference competition. In exploitative competition, the interactions between competing individuals are indirect, mediated through a shared resource. In other words, the effect that one individual has on the other is caused by depletion of a resource that both species require. Interference competition, however, involves direct interactions between competing individuals – in the anoles, territoriality is the primary form of interference competition. My interests lie in explaining the evolution and ecology of “interspecific interference competition,” or aggressive interactions between species. The anoles provide plenty of examples of this; I’ve seen territorial displays, chases, or fights in almost every possible species combination. There’s a lot of work to be done before we fully understand the interactions among species in this new community of exotic anoles!

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America's Birdiest County

 Posted by at 6:59 pm on May 13, 2010
May 132010
 

Question: If you wanted to see as many North American bird species as possible, and you could visit just one county in the United States to do it, where would you go? Would you choose a county that shares a border with Mexico? These counties contain well-known North American bird “hotspots,” places that birders go to see birds they can’t see anywhere else, like the Lower Rio Grande Valley (Texas’s Brewster County), Big Bend National Park (Texas’s Cameron County), and the incredible Chiricahua Mountains (Arizona’s Cochise County). Maybe somewhere in South Florida, like Miami-Dade County, would be a good option – in addition to several resident specialties, many temperate-breeding birds winter there, and there are many introduced exotic species to be seen as well. On the other hand, perhaps a famous “migrant trap” like Cape May County, New Jersey would give you the best chance of amassing a big species list.

These are all worthy choices; there is great birding to be had in each of these counties (and many others). But there can only be one “America’s Birdiest County.” America’s Birdiest County (ABC) is a competition that’s been run annually since 2003. During the competition, teams of birders count every bird they can find in a single weekend, chosen by the county’s ABC organizers (typically in April or May, when locally-breeding birds have already arrived but non-resident migrants are still passing through). The county with the biggest species list wins! So, I’ll repeat the question posed at the beginning of this post: Where would you go? Where is America’s Birdiest County?

An adult Spotted Owl (Strix occidentalis), photographed in Los Angeles County in 2008. The Spotted Owl is a regular breeder in LA County.

The answer may surprise you. For four years running, Los Angeles County has won the ABC competition, with more than 250 species observed each year. Most people think of Los Angeles as a sprawling sea of concrete, and to some extent that’s true. But there’s more to LA County than the City of Los Angeles. Angelenos often say things like “where else can you go surfing in the morning and skiing in the afternoon?” In other words, where else can you go birding at a coastal lagoon in the morning and a 10,000′ summit in the afternoon? LA County is exceptionally varied, and its birdlife reflects its ecological diversity.

The official 2010 ABC results won’t be announced until June, but LA County will undoubtedly be a strong contender. A whopping 271 species were seen by more than sixty birders scouring the county for 3 days in late April. This is the second-highest total in the history of ABC (the highest was 272, the LA County tally in 2007). The 2010 list included some impressive rarities, like Yellow-billed Loon, Sabine’s Gull, and Hooded Warbler.

To my Los Angeles readers: did you know that you live in one of the most bird-rich places in North America? Get outside this weekend and see some birds! And to the rest of my readers: you should go birding this weekend too. See if you can beat us :)

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BioBlitz report

 Posted by at 5:00 am on May 7, 2010
May 072010
 

The Biscayne National Park BioBlitz, a 24-hour species inventory run jointly by the National Geographic Society and National Park Service, ran from noon on Friday to noon on Saturday. The BioBlitz occurs at a different national park each year, and this year I just happened to be in the right place at the right time – I was in Miami for my fieldwork at the same time the BioBlitz was running at Biscayne NP! Because my anole research is partially funded through National Geographic’s Young Explorers Grant program, I was invited to participate as an “expert” – a somewhat ironic title, since this would be my first time in Biscayne NP, but I enthusiastically accepted the invitation nonetheless.

During the BioBlitz, a male Bobolink (Dolichonyx oryzivorus) feeds in the grass at the Elliott Key Visitor Center.

James, Miles and I spent both days of the BioBlitz on Elliott Key, the largest island in the park. Our task: to lead bird and reptile survey walks with groups of volunteers. Elliott Key makes a pretty good “migrant trap” – it’s situated at the southern tip of the Florida peninsula, so it’s the first point of land that many neotropical migrant birds encounter after a long flight from Caribbean or South American wintering grounds. During the BioBlitz, several Bobolinks and Dickcissels foraged in the grassy lawn around the Elliott Key Visitor Center, while Bay-breasted, Cape May, Blackpoll, Black-throated Blue, and Palm Warblers patrolled the forest edges. Reptile diversity on the island was much more modest; we saw mostly Cuban brown anoles (Anolis sagrei) and a few native green anoles (A. carolinensis). James spotted a few black racers (Coluber constrictor), which probably feed on the island’s anoles.

A crew of bird banders set up mist nets in the forest on Elliott Key. Here, one of the banders shows a male Northern Cardinal (Cardinalis cardinalis) to BioBlitz volunteers.

The BioBlitz had an atmosphere of collegiality and cooperation. Science can be a pretty competitive endeavor at times, but none of that was on display at Biscayne NP. On one of our survey walks, for example, a member of our group spotted a beautiful ground beetle. It was matte black with iridescent deep-blue elytra margins and a matching blue underside. Now, I don’t pretend to know my beetles. Fortunately for me, however, several entomologists were hard at work back at the Visitor Center. We found the nearest entomologist, identified the beetle with her help, and added it to the day’s species count! To me, this experience epitomized the BioBlitz: scientists were helping scientists, and the public was getting involved at every stage. If only more science could be conducted this way!

A Cuban Treefrog (Osteopilus septentrionalis), one of the 810 species already identified from the Biscayne NP BioBlitz. Photographed at nearby Everglades NP.

At the end of the weekend, as part of the BioBlitz’s closing ceremonies, I was interviewed on stage by Bob Hirshon, host of the nationally syndicated Science Update radio show and podcast. Bob was a perfect MC for the closing ceremonies – his enthusiasm really got the audience involved! As of the closing ceremonies, we had identified 810 species in the park, and that number will undoubtedly grow as the specimens collected are examined in more detail over the coming weeks. Even more impressively, the BioBlitz involved more than 2500 people, including over 1300 students from Miami-Dade County schools, many of whom had never visited the park before.

All in all, it was a great weekend – I met new friends at National Geographic and the NPS, saw a lot of cool organisms, and got to share my enthusiasm for nature with many BioBlitz volunteers. I’ll definitely participate in more BioBlitzes in the future, and when the BioBlitz comes to a park near you, you should participate too!

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