American students going wild during their Spring Break week-long recess in Cancun, Mexico on March 10, 2007. (Photo by Keystone USA/ZUMA Press/Rex Features/Shutterstock)

Global wildlife populations will decline by 67% by 2020 unless urgent action is taken to reduce human impact on species and ecosystems, warns the biennial Living Planet Index report from WWF (World Wide Fund for Nature) and ZSL (Zoological Society of London). From elephants to eels, here are some of the wildlife populations most affected by human activity. Here: The maned wolf is among the large mammals in the Brazilian Cerrado that are threatened by the increasing conversion of grasslands into farmland for grazing and growing crops. (Photo by Ben Cranke/Nature Picture Library/Alamy Stock Photo)

The extremely rare Kelvin-Helmholtz cloud formation lurking in the skies over Northumberland in North East England on December 5, 2023. The distinctive formation gets its name from scientists Lord Kelvin and Hermann von Helmholtz who studied the physics behind the rare cloud. (Photo by Ian Davison/South West News Service)

1st prize in the People Observed Portraits Stories category. Carla Kogelman, the Netherlands. The photo shows Hannah and Alena, two sisters living in the rural village of Merkenbrechts, Austria. (Photo by Carla Kogelman/World Press Photo)

Chloe Lewis attends “The Ony Way Is Essex” season finale filming in Wintney, Hook, England on October 29, 2017. (Photo by Beretta/Sims/Rex Features/Shutterstock)

Kazakhstan's Elena Rybakina (L) checks on France's Alize Cornet after resulting injured during their women's singles tennis match on the fourth day of the 2023 Wimbledon Championships at The All England Tennis Club in Wimbledon, southwest London, on July 6, 2023. (Photo by Glyn Kirk/AFP Photo)

English actress Liz Hurley, 55, poses topless in the snow in a photo taken by her son in United Kingdom at the end of January 2021. Brit stripped to white bikini bottoms from her own swimwear range and draped herself in a coat. (Photo by Instagram/The Sun)

Colombian-Spanish actress Juana Acosta attends the Fotogramas Awards 2012 at Joy Eslava Club on March 12, 2012 in Madrid, Spain. (Photo by Carlos Alvarez/Getty Images)