By Priya Amin
What causes species loss? As biodiversity has become increasingly threatened, the call to understand the impact of human activity on species around the world has become particularly urgent. Drivers of species loss include climate change, pollution, and habitat conversion. Climate change has been linked to rising levels of carbon dioxide, which are attributable to human activity (1). Similarly, pollution is a byproduct of human expansion; undoubtedly, pollutes like fertilizer run-off and plastic waste have negatively impacted many land and marine ecosystems (2,3). However, while climate change and pollution are key drivers of species loss, both of these factors only indirectly stem from human expansion.
Habitat conversion for human development, on the other hand, directly trades economic profit for habitat loss. Therefore, as the demand for more resources inevitably rises as a result of population growth, so will the rate of habitat conversion. In addition, habitat conversion is deeply rooted within the story of human migration and expansion. Looking toward the future, scientists’ sizable estimates of habitat conversion stem from humanity’s growing stewardship of Earth’s land and resources. Economic activity that causes habitat loss includes urbanization, mining, water development, and agriculture. However, a leading cause of global change is likely the growing human modification of environments for agriculture (4). To supplement the growing need for food and biofuels, it is projected that approximately one billion additional hectares of agronomic land will be developed in the next few decades (5).
As a result of agricultural land development, an ecosystem experiences a reduction in its ability to foster biodiversity (6). This is particularly crucial to the survival of biodiversity hotspots, which are characterized by tremendous habitat loss and a subsequent loss of endemic plant species (7). For example, the Cerrado biome, a recognized biodiversity hotspot, is home to a variety of unique habitats, including dense woodlands, open grasslands, and dry forests; it is also the richest savannah ecosystem in the world (8). The agricultural potential and climatic suitability of the area has led to rapid human occupation. Cattle ranching and intensive farming in the Cerrado biome have caused tremendous decline in natural habitat cover (8).
The drastic loss of spatially consistent natural cover in the Cerrado biome denotes the decline of many endemic plant species, which is also mirrored in the Atlantic rain forest biome. The forest-grassland mosaic of Rio Grande do Sul, Brazil has been largely converted for agri- and silviculture.9 Due to extensive logging practices, the area’s Araucaria broadleaf forest is only a mere fraction of its original extension, and the Araucaria angustifolia species has been recently placed on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Endangered Species (9). According to a study by Hermann and colleagues, land conversion rates far outweigh preservation attempts in the area. Collecting data from satellite images, silviculture in the area was expanded by 94% over the six-year study, and grassland was the main target for agricultural land conversion. On a larger scale, this reflects global developments in temperate grasslands (9).
An overwhelming number of studies have studied the impact of agricultural habitat conversion on birds, which are often used as indicators of biodiversity status. They play vital roles in many ecosystems, ranging from pollination and seed dispersal to insect control and nutrient cycling. It has been estimated that approximately a fifth to a quarter of pre-agricultural bird numbers have been lost due to agricultural development (6). In particular, avian breeding success is impacted by agricultural land conversion. A study conducted by Cartwright et al. concluded that the formerly Critically Endangered Mauritius kestrel Falco punctatus experiences a decline in breeding success as the area of agriculture near a nest site is increased (10). This may be attributable to the increasing spatial variation in the availability of native prey, which is exasperated by land conversion. In addition, loss of farmland bird populations has been observed in Europe. For example, farmland bird populations that are dependent on key aspects of these agro-ecosystems experienced a 40% decline between 1980 and 2000 (1). The status of bird populations is a crucial predictor of how other species in ecosystems will be impacted. Unfortunately, estimates based on current agricultural trends indicate that avian species, and biodiversity, will continue to decline (6).
Agricultural habitat conversion has caused much biodiversity and species loss throughout the world. The impact on biodiversity hotspots is especially alarming. Agricultural land conversion of these species-rich areas has been especially detrimental to biodiversity. The startling decline in avian numbers is an ominous sign that many species are threatened by the growing trends in agriculture.6 Thus, with an increasing human population, it is incumbent that special care is taken to protect encroached environments and endangered species.
Priya Amin ’19 is a sophomore in Pforzheimer House concentrating in Integrative Biology.
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Categories: Spring 2017