The fourth annual BigPicture Natural World Photography Competition aims to celebrate the diversity of life on Earth, and encourages people to protect and conserve it. Here: “The Salmon Catchers”. Terrestrial Wildlife. To capture this view of a mother grizzly bear and her cub, photographer Peter Mather set up a camera trap on a log that he knew the bears tended to traverse while fishing for salmon, in the Yukon River watershed in Canada. (Photo by Peter Mather/BigPicture Natural World Photography Competition 2017)

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)

A beggar who lay at the side of a road pretending he had no legs was moved on by police who made him stand up and walk away. The man lay slumped on his front in Chengdu, in Sichuan Province, China, with his legs tucked under him, and his jeans stretched out to make it appear he had no legs. He is approached by a police officer, who bends down and talks to him for some moments. The officer then reaches out and helps the man to his feet before guiding him across the road. Chengdu is one of a number of cities where officials have tried to clamp down on begging. (Photo by Rex Features)

“After taking LSD. I lighting up a candle in the middle of the wood and during the 30 secondes of exposure, i make a meditation about the holism of nature surrounding me. Feeling the crystal vibration irradiating from the center of the Gaia mother earth. So in this picture i try to show you the magic, sacred metaphysical quality of the nature and new age bullshiting you”. – Benoit Paillé. (Photo by Benoit Paillé)

Swedish brown bears “Fred” and “Frode” play in the snow on January 30, 2014 at the Natur- und Umweltpark (NUP) animal park in Guestrow, northeastern Germany. Despite of icy temperatures, the bear brothers took a break from their winter rest. (Photo by Bernd Wuestneck/AFP Photo/DPA)

Bjorn, aged 5, smiles as he poses with a Owl butterfly during an event to launch the Sensational Butterflies exhibition at the Natural History Museum in London, Britain March 23, 2016. The exhibition opens to the public on March 24 and runs until September 11. (Photo by Dylan Martinez/Reuters)

“Tasty Nature” by Dipesh Bhatt. “The blue banded bee (Amegilla cingulata) is pointing this sheath towards the flowers in preparation for sipping nectar”. Taken in Gujarat, India. (Photo by Dipesh Bhatt/2016 Royal Society of Biology Photographer of the Year competition)

A woman tour skates on the frozen lake of Orlangen, south of Stockholm, Sweden, on December 23, 2016. Tour skating is recreational long distance ice skating on natural ice particularly popular in the Nordic countries. (Photo by Tobias Roestlund/AFP Photo/TT News Agency)