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Researchers at Lin­coln Park Zoo and North­ern Illi­nois Uni­ver­sity have dis­cov­ered a new cul­prit con­tribut­ing to amphib­ian decline and altered mam­mal dis­tri­b­u­tion through­out the Mid­west region — the inva­sive plant Euro­pean buck­thorn (Rham­nus cathar­tica). This non-​native shrub, which has invaded two-​thirds of the United States, has long been known to neg­a­tively impact plant com­mu­nity com­po­si­tion and for­est struc­ture, but these two inno­v­a­tive stud­ies slated to pub­lish in upcom­ing edi­tions of the Jour­nal of Her­petol­ogy and Nat­ural Areas Jour­nal demon­strate how this shrub neg­a­tively impacts native amphib­ians and affects habi­tat use by mam­mals includ­ing increased preva­lence of coy­otes and other carnivores.

Amphib­ians are fac­ing an extinc­tion cri­sis world­wide, with 165 species likely hav­ing gone extinct in recent years accord­ing to the Amphib­ian Ark, a coali­tion of con­ser­va­tion­ists devoted to seek­ing solu­tions to the decline. Lin­coln Park Zoo Rein­tro­duc­tion Biol­o­gist Alli­son Sacerdote-​Velat, Ph.D. and North­ern Illi­nois Uni­ver­sity Pro­fes­sor of Bio­log­i­cal Sci­ences Richard King have iden­ti­fied Euro­pean buck­thorn as a con­trib­u­tor to amphib­ian decline in the Chicagoland area. The plant releases the chem­i­cal com­pound emodin, which is pro­duced in the leaves, fruit, bark and roots of the plant, into the amphib­ian breed­ing pond envi­ron­ment at var­i­ous times of year. Sacerdote-​Velat and King’s research has found that emodin is toxic to amphib­ian embryos, dis­rupt­ing their devel­op­ment, pre­vent­ing hatching.

“Lev­els of emodin in the envi­ron­ment are great­est at leaf out, which is occur­ring right now in early spring. This coin­cides with breed­ing activ­ity of sev­eral early-​breeding Mid­west­ern amphib­ian species includ­ing west­ern cho­rus frogs and blue-​spotted sala­man­ders,” explained Sacerdote-​Velat. “Sev­eral amphib­ian species exhibit low hatch­ing rates in sites that are heav­ily infested with Euro­pean buckthorn.”

The Chicago Wilder­ness 2004 Wood­land Audit found that in the Chicagoland area alone, more than 26 mil­lion stems of Euro­pean buck­thorn exist with a den­sity of 558 stems per acre. Whilst this study specif­i­cally found emodin to detri­men­tally impact devel­op­ment of two species of frogs, West­ern cho­rus frogs and African clawed frog (a com­mon test species for envi­ron­men­tal tox­i­c­ity stud­ies), Sacerdote-​Velat and King hypoth­e­size that emodin may impact the repro­duc­tive suc­cess of other frog species in regions where buck­thorn is not native.

“West­ern cho­rus frogs are quite com­mon in the Mid­west, and peo­ple in Illi­nois who have never seen them have prob­a­bly heard them in the spring­time,” said King, who has con­tin­ued to con­duct research with Sacerdote-​Velat after hav­ing served as her Ph.D. adviser at NIU.

Addi­tion­ally, new research from the zoo’s Urban Wildlife Insti­tute reveals how the pres­ence of the inva­sive shrub in for­est pre­serves and nat­ural areas cor­re­lates to increased preva­lence of car­ni­vores. Pre­vi­ous research by Ken Schmidt of Texas Tech Uni­ver­sity and Chris Whe­lan of Illi­nois Nat­ural His­tory Sur­vey doc­u­mented that these car­ni­vores can prey more eas­ily on native bird eggs and nestlings such as robins when nests are built in buck­thorn and hon­ey­suckle com­pared to nests built in native shrubs or trees.

“The rela­tion­ship between inva­sive plants and wildlife is com­plex. This is the first study of its kind to inves­ti­gate the asso­ci­a­tion between buck­thorn and habi­tat use by mam­mal species. We know based on prior research that birds which build nests in buck­thorn are more sus­cep­ti­ble to pre­da­tion. Our study found that the pres­ence of buck­thorn alters wildlife dis­tri­b­u­tion and attracts some car­ni­vore species. We now know that there are sig­nif­i­cantly more coy­otes, rac­coons and opos­sums in buck­thorn invaded areas, and sig­nif­i­cantly fewer white-​tailed deer.”

Magle hypoth­e­sizes that the car­ni­vores could be drawn to buck­thorn areas because birds and their nests are eas­ier to prey upon. He sug­gests that deer may be avoid­ing these areas because buck­thorn is an unde­sir­able food source, and also due to the increased preva­lence of coy­otes. Research shows that deer fawns are a rel­a­tively com­mon food item for Chicago-​area coyotes.

Both Magle and Sacerdote-​Velat agree that these find­ings are sig­nif­i­cant. The stud­ies demon­strate how the high-​density preva­lence of this non-​native plant is shift­ing pop­u­la­tion dynam­ics and neg­a­tively impact­ing a vari­ety of native ani­mal pop­u­la­tions. They sug­gest land own­ers and man­agers should con­sider inva­sive species man­age­ment and habi­tat restora­tion. In some areas, like Lake County For­est Pre­serve Dis­trict where Sacerdote-​Velat works reg­u­larly, ecol­o­gists and land man­agers have been com­mit­ted to remov­ing buck­thorn from the area. “I hope that this new research will encour­age other regions and land man­agers to take swift and deci­sive action to work to remove this inva­sive plant,” she said.

(Source: Lin­coln Park Zoo press release, 01.05.2013; Wikipedia)