Every time, a natural habitat is converted into a land for agricultural or residential purposes, it is the small predators, especially small invertebrates like spiders and ladybirds, which lose their homes as well as lives, as per a first of its kind global study on the impacts of human land-use on different groups of animals.
The findings published in the journal, Functional Ecology, also found that small ectotherms — cold blooded animals such as invertebrates, reptiles and amphibians, large endotherms like mammals and birds and fungivores ie animals that eat fungi were also disproportionally affected.
But, the loss of large herbivores will also likely to have important effects on ecosystem functioning, for example increasing the risk of rodent borne human disease, warn the researchers who had analysed over one million records of animal abundance at sites ranging from primary forest to intensively managed farmland and cities.
The data represented over 25,000 species across 80 countries. Species were grouped by size, whether they were warm or cold blooded and by what they eat. Species ranged from the oribatid mite weighing only 2x10-6g, to an African elephant weighing 3,825kg.
“Normally, when we think of predators, we think of big animals like lions or tigers. These large predators did not decline as much as we expected with habitat loss, which we think may be because they have already declined because of human actions in the past (such as hunting). We find small predators - such as spiders and ladybirds - to show the biggest declines,” said Dr Tim Newbold from University College London and lead author of the research.
The results indicate that the world's ecosystems are being restructured with disproportionate losses at the highest trophic levels (top of the food chain).
“We know that different types of animals play important roles within the environment - for example, predators control populations of other animals. If some types of animals decline a lot when we lose natural habitats, then they will no longer fulfil these important roles.” said Dr Tim Newbold.
The conversion of land to human use is associated with the removal of large amounts of natural plant biomass, usually to give space for livestock and crops. As you go up the trophic levels (food chain), resource limitations are compounded through a process known as bottom-up resource limitation, said the study which is part of the PREDICTS project exploring how biodiversity responds to human pressures.
The researchers analysed 1,184,543 records of animal abundance in the PREDICTS database, gathered from 460 published scientific studies. This database included all major terrestrial vertebrate taxa and many invertebrate taxa (25,166 species, 1.8% of described animals).
Species were sorted into functional groups defined by their size, trophic level (what they consumed) and thermal regulation strategy (warm or cold blooded). The type of land-use at each of the 13,676 sample sites was classified from the description of the habitat in the source publication. The six broad categories were primary vegetation, secondary vegetation, plantation forest, cropland, pasture and urban. Three levels of human use intensity were also recorded: minimal, light and intense.
