Free-roaming domestic cats (Felis catus) are widely understood to have substantial negative impacts on wildlife. The International Union for the Conservation of Nature (IUCN) lists cats among the world’s worst non-native invasive species, and cats on islands worldwide have contributed to 33 species extinctions (Lowe et al. 2000, Medina et al. 2011). In the United States free-roaming cats are the top source of direct anthropogenic mortality to birds and mammals, killing approximately 2.4 billion birds and 12.3 billion mammals each year (Loss et al. 2013).

The indirect impacts of cats on wildlife are less obvious, but one of the greatest emerging threats from free-roaming cats is infection with Toxoplasma gondii. T. gondii is a parasitic protozoan that can infect all warm-blooded species but relies on felids to complete its life cycle. According to a new study published in EcoHealth, feral cats are likely driving white-tailed deer (Odocoileus virginianus) infections in northeastern Ohio (Ballash et al. 2014). Cats that host T. gondii excrete oocysts into the environment in their feces, and a single cat can deposit hundreds of millions of oocysts, which may remain infectious for up to 18 months (Tenter et al. 2000).

The study’s authors collected white-tailed deer samples at the Cleveland Metroparks as part of a deer management program. Cat serum samples were collected from cats in a trap, neuter, release (TNR) program in the Greater Cleveland area. TNR programs spay/neuter feral cats and then release them into the environment. Nearly 60% of white-tailed deer and 52% of feral cats tested positive for T. gondii. Older deer and deer in urban environments were more likely to be infected, suggesting horizontal transmission from environmental exposure.

The study’s findings have implications for people as well. Widespread environmental contamination increases the likelihood of human infections. In people, infection has been linked to schizophrenia and can lead to miscarriages, blindness, memory loss, and death (Torrey and Yolken 2013, Gajewski et al. 2014). Due to the creation of tissue cysts in infected deer, people that consume undercooked venison can also acquire T. gondii and the subsequent disease, toxoplasmosis.

The Wildlife Society actively supports the humane removal of feral cats from native ecosystems. See our position statement and fact sheet for more information on how feral and free-ranging domestic cats impact wildlife.

This article was written in cooperation with the American Bird Conservancy.

Flying dragons in Borneo adopt Christmas colors to mimic the red and green hues of falling leaves in an effort to hide from predatory birds, according to new research. But the red and green colors of different Draco populations have nothing to do with a festive spirit.

“It’s a cool finding because these gliding lizards are matching the colors of falling leaves and not the leaves that are still attached to the tree,” said Danielle Klomp, a researcher at the University of Melbourne and the University of New South Wales and the lead author of the study released today in Biology Letters. “In the mangrove population the leaves on the trees are bright green, but turn red shortly before falling to the ground, and it is this red color that the lizards mimic in their gliding membranes. This allows them to mimic a moving part of the environment—falling leaves—when they are gliding.”

The wing-like membranes of gliding Dracos match the colors of falling leaves in their habitat.
Image Credit: Danielle Klomp

The gliding lizard Draco cornutus uses extendable membranes to escape from predators in the treetops by letting them glide through the forest—the only lizard genus known to fly in the world. The lizards typically only come down to the ground when the females lay eggs in the dirt.

Klomp and a team of others working on the project observed two different populations of flying dragons on the island and found that each had a distinct set of colors that matched their respective habitats.

While the coastal mangrove population matched the red color of falling leaves, a population of flying lizards in the lowland rainforest took on more of a dark brown and green color to match local leaves in that area.

“Perhaps these populations may have originally had the same gliding membrane colors. But as they have moved into different forest types their colors have adapted to closely resemble the colors of falling leaves in the different forests,” Klomp said, adding that the phenomenon was known as divergent evolution.

She said that birds can perceive the same colors humans can as well as ultraviolet light, so the colors on lizard membranes could confuse them.

The researchers spent hours filming lizard flights in an attempt to determine whether they also used these colors to communicate the same way other reptiles do but they found it was strictly used for camouflage.

Feisty invasive fire ants known for their painful bite could be helping the spread of invasive plant species in the parts of the North American Northeast in what some scientists call “invasional meltdown.”

“We were interested in finding out whether the arrival and spread of this ant was going to change plant dispersal because it acts differently from native ants in our area,” said Megan Frederickson, an evolutionary biologist at the University of Toronto and senior author of the paper released Dec. 23 in Proceedings of the Royal Society B.

Image Credit: K.M. Prior

Frederickson and other researchers conducted a study using dozens of miniature ecosystems created in kiddie pools north of the Canadian city in the university’s Koffler Scientific Reserve to see the different ways the invasive Myrmica rubra – also known as the common red ant – interacted with plant seeds compared to a native species of ant (Aphaenogaster rudis).

Both ants are known to be seed dispersers. The native species is found from Quebec throughout the Eastern seaboard down to South Carolina, while the invasive fire ants have been spreading over various parts of North America during the past few decades. The fire ants have been here for some time, and Frederickson said they are believed to have come in with agricultural shipments but the researchers wanted to know if the European ants would favor invasive seeds from a plant that came from their native Europe over local plant varieties.

They needed 42 kiddie pools to create all the different ecosystem mixtures between the two kinds of ants and four plant species – three native varieties and one invasive species: the greater celandine (Chelidonium majus).

They found that the invasive ants tended to help the spread of the invasive celandine plants.

“The kiddie pools that had the invasive ants in them were completely run over by this invasive plant,” Frederickson said.

The greater celandine is a perennial plant commonly found in roadside ditches and forest edges in North America. Its seeds can bud anytime whereas the native plants they used in the experiment depended on seasonal conditions. So even while the researchers noticed the invasive ants were dispersing seeds from the native plants as well as the invasives, the invasive plant benefited more than the others because it wasn’t dependent on seasonal conditions.

“It’s something called invasional meltdown,” she said, speaking about the phenomenon that occurs when one invasive species helps another.

Image Credit: K.M. Prior

“Because we don’t have any historical data, we actually don’t know how long this might have been going on for,” she said. “The ant may have been helping it spread all along but we never knew it until now.”

The implications are that the ants – and potentially other invasive species – could be altering ecosystems in complex ways.

“The ants reach pretty high abundances where they’ve been introduced, especially in very moist systems,” Frederickson said. “We think that they can really change communities of arthropods.”

Effects like this are poorly studied though, and many invasive species tend to be studied in isolation without looking at the way they interact with other species.

But she said that the ants could be helping plants like the greater celandine spread into more pristine forest ecosystems.

“This is a case of the plant potentially piggybacking off the success of the ant,” she said. “The results might make ecologists wonder how commonly these kinds of invasional meltdowns are happening.”