Defaunation
[4] The growth of the human population, combined with advances in harvesting technologies, has led to more intense and efficient exploitation of the environment.
[12] A 2021 study found that only around 3% of the planet's terrestrial surface is ecologically and faunally intact, with healthy populations of native animal species and little to no human footprint.
[13][14] In November 2017, over 15,000 scientists around the world issued a second warning to humanity, which, among other things, urged for the development and implementation of policies to halt "defaunation, the poaching crisis, and the exploitation and trade of threatened species.
In Brazilian Amazonia, 23 million vertebrates are killed every year;[17] large-bodied primates, tapirs, white-lipped peccaries, giant armadillos, and tortoises are some of the animals most sensitive to harvest.
[21] Most affected species undergo pressure from multiple sources but the scientific community is still unsure of the complexity of these interactions and their feedback loops.
[5] Large mammals are often more vulnerable to extinction than smaller animals because they require larger home ranges and thus are more prone to suffer the effects of deforestation.
[24] A case study from Amazonian Ecuador analyzed two oil-road management approaches and their effects on the surrounding wildlife communities.
The results suggested that higher levels of fragmentation within the fish-bone pattern led to the loss of species and decreased diversity of large vertebrates.
[27] Human impacts, such as the fragmentation of forests, may cause large areas to lose the ability to maintain biodiversity and ecosystem function due to loss of key ecological processes.
[5] Fragmentation also has cascading effects on native species, beyond reducing habitat and resource availability; it leaves areas vulnerable to non-native invasions.
[4][5][9] These regions, which include the Brazilian Amazon, the Congo Basin of Central Africa, and Indonesia, experience the greatest rates of overexploitation and habitat degradation.
[34] International trade in wild animals, as well as extensive logging, mining and agriculture operations, drive the decline and extinction of numerous species.
Loss of genetic diversity lowers the ability of a population to deal with change in their environment and can make individuals within the community homogeneous.
There are three non-mutually exclusive conclusions as to the consequences on tropical forest plant communities: One recent study analyzed seedling density and composition from two areas, Los Tuxtlas and Montes Azules.
Los Tuxtlas, which is affected more by human activity, showed higher seedling density and a smaller average number of different species than in the other area.
[38] As a result, a plant community that relies on animals for dispersal could potentially have an altered biodiversity, species dominance, survival, demography, and spatial and genetic structure.
Bird and bat species (many of who are small bodied seed dispersers) rely on mineral licks as a source of sodium, which is not available elsewhere in their diets.
In defaunated areas in the Western Amazon, mineral licks are more thickly covered by vegetation and have lower water availability.
[42] According to a 2022 study published in Science, terrestrial mammal food web links have declined by 53% over the past 130,000 years as a result of human population expansion and accompanying defaunation.
[43] Changes in predation dynamics, seed predation, seed dispersal, carrion removal, dung removal, vegetation trampling, and other ecosystem processes as a result of defaunation can affect ecosystem supporting and regulatory services, such as nutrient cycling and decomposition, crop pollination, pest control, and water quality.
