A Second Miami Tiger Beetle Population Discovered
Note: This post was largely written in August, however I held off publishing due to the sensitive nature of this discovery. This Friday the U.S. Fish and Wildlife Service proposed listing the Miami tiger beetle as an endangered species and announced the existence of a second population of the MTB. With this official confirmation I’m publishing this post in hopes of contributing some context and further information about this population.
The story of the Miami tiger beetle, Cicindela floridana, a beautifully iridescent tiger beetle presumed extinct but rediscovered in 2007 is unique. This fiercely predatory beetle is a south Florida endemic only known from pine rocklands, a habitat once common in Miami-Dade county but, due to extensive development, today only 1.8% of the metro Miami-Dade rocklands remain.
The entomologist Frank N. Young Jr., an 18 year old student at the time, discovered the Miami tiger beetle from pine rocklands in 1934 at a site in northern Miami-Dade county. However, by 1947 this habitat was lost to development as the native pine rocklands were transformed into the neighborhoods of north Miami and Miami Shores (below).
In 2007, after a 73 year absence and presumed extinction, the Miami tiger beetle was rediscovered near Zoo Miami in pine rocklands. This site is part of the Richmond Heights pine rocklands, the largest contiguous remaining areas of this habitat in metro Miami-Dade. Spurred by this rediscovery entomologists surveyed pine rocklands throughout southern Florida in search of the Miami tiger beetle.
Extensive surveys were conducted in both scrub habitats and most of the pine rockland sites in Miami-Dade, Ft. Lauderdale and Palm Beach Counties (Knisley, 2008). Most were unsuitable probably because they were too densely vegetated or the substrates were mostly oolitic limestone rock with few or no sand patches (Knisley et al. 2014).
Despite these efforts in the years since its remarkable rediscovery the Miami tiger beetle had only been found at a handful of directly adjacent sites in the Richmond Heights pine rocklands. Even the known population is few in number (under a hundred adult beetles observed) and face further threats of vegetation encroachment and potential habitat development (see here for more).
This changed in July when Jimmy Lange, a field botanist at Fairchild Tropical Botanic Garden, and Alyssa Dawson, an intern from Ohio University, were surveying an undisclosed patch of pine rocklands for rare plants (namely Brickellia mosieri, an endangered species) when, as Lange describes it, “[i]n my meanderings I was [documenting] other rare species as I encountered them … when I bumped into a tiger beetle.” But this was not just any tiger beetle, Lange and Dawson found three Miami tiger beetles (Cicindela floridana).
Lange and Dawson’s discovery offers a small boost to the hopes for the survival of the Miami tiger beetle. But even with the discovery of the second population the MTB is still in danger. The MTB habitat, pine rockland, has been extensively developed and today only 1.8% of the metro Miami-Dade pine rocklands remain. These habitats are also under the constant threat of vegetation encroachment primarily due to the lack of controlled burns (which pine rocklands depend upon).
A major question regarding this second population of MTBs is whether the discovery of new populations would alter the expert’s rating of the species as seriously imperiled and recommendation for formal protections (Knisley et al. 2014). In brief this second population does not significantly alter the Miami tiger beetle’s current standing. First, this “population” is represented by three observed beetles and thus likely does not provide a sufficient number of individuals to contribute to the species survival. Second, Knisley et al. (2014) account for the existence of other populations in their recommendation methods:
Examples of our grading system are as follows: A 1 would be comparable to the NatureServe grade of 1, usually with five or fewer known populations and significant threats; a 1+ would be at the upper range of these factors and 1- at the lower range.
For the 1 +/- grade given by Knisley a species must face significant threats which is absolutely the case for the MTB. Most significantly both populations face the “loss, degradation, and fragmentation” (USFWS) of habitat, primarily from the constant encroachment of vegetation, both ecological succession due the lack of fires and invasive species.
Of particular note the U.S. Fish and Wildlife Service did not release the location of this new population due to the threat of collection:
Tiger beetles are in high demand and avidly collected. We are aware of internet advertisements for the sale and trade of other florida tiger beetles.