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)

Igor Armicach, a doctoral student at Hebrew University's Arachnid Collection, looks onto giant spider webs, spun by long-jawed spiders (Tetragnatha), covering sections of the vegetation along the Soreq creek bank, near Jerusalem, Israel on November 7, 2017. (Photo by Ronen Zvulun/Reuters)

David Goffin of Belgium meets a koala during a promotional event for the Australian Open tennis tournament at Melbourne Park on January 17, 2018. (Photo by Fiona Hamilton/Reuters/Tennis Australia)

Soldiers stand in line outside portable toilets during a military parade to celebrate the 206th anniversary of Colombia's independence in Bogota, Colombia, July 20, 2016. (Photo by John Vizcaino/Reuters)

Tourists from the Middle East take pictures at Vrelo Bosne nature park in Ilidza near Sarajevo, Bosnia and Herzegovina, August 19, 2016. They discovered mountainous Bosnia, where half the population is Muslim, after the Arab Spring which destabilized many traditional holiday destinations such as Libya, Tunisia and Egypt. (Photo by Dado Ruvic/Reuters)

Members of the traditional Los Historiantes dance group perform during a welcoming ceremony for Catholic devotees known as "Cumpas", in the town of Cuishnahuat, El Salvador November 26, 2015. The Catholic people of the El Balsamo mountain range meet in the village of Cuishnahuat in November to celebrate the 'friendship' between their respective patron saints in a ceremony that has been carried out for more than 300 years, according to the government. (Photo by Jose Cabezas/Reuters)

Activists participate in the Walk of Lesbian and Bisexual Women in Paulista Avenue, SP. The act was organized by the LGBT (lesbian, gay, bisexual and transgender) in São Paulo, Brazil, on June 2, 2018. (Photo by Cris Faga/NurPhoto via Getty Images)

A wild elephant that strayed into the town moves through the streets as people follow at Siliguri in West Bengal state, India, Wednesday, February 10, 2016. The elephant had wandered from the Baikunthapur forest on Wednesday, crossing roads and a small river before entering the town. The panicked elephant ran amok, trampling parked cars and motorbikes before it was tranquilized. (Photo by AP Photo)