Similarities in ecological dynamics remain between natural and arable land, including the occurrence of trophic interactions across the food chain, which despite being a potential threat of increasing crop losses, may also provide key benefits to improve agricultural practices.
Food Chain. Image Credit: BlueRingMedia/Shutterstock.com
An ecological perspective of agriculture
According to the Food and Agriculture Organization of the United Nations (FAO), an estimated 5 billion hectares of land, equivalent to 38% of the total global land surface, is currently used for agricultural practices. Despite spatial, temporal, and cultural variations in agricultural systems, the overarching commonality throughout agriculture remains the use of a relatively limited number of plant or animal species that are used for crop production, food supply, or animal feed.
Our reliance upon a small number of species used for agricultural purposes has made crops and livestock the most evolutionarily successful animal species on this planet. One astounding example is that chickens alone represent over 80% of all birds on earth. Ecologically, species related to agriculture also provide valuable insight into the dynamics of diversity and stability that are extensively modified in agricultural systems.
This is particularly important as ecosystems rely on the diversity, richness, and interaction of species to ensure long-term stability. However, human activity has modified these natural processes extensively through agriculture.
A fundamental concept of ecology is the functional position of a species within the food chain, which can be referred to as trophic level. If the trophic system of an ecosystem is modified, by human activity, for example, the subsequent modifications may generate unpredictable changes for the interactions between species of different trophic groups, so-called trophic interactions.
As plants, crops occupy a position in the ecosystem at the base of the food chain. Similarly, most livestock occupies a mid-level trophic position as herbivores. Accordingly, crops and livestock experience trophic interactions from species below and higher up in the trophic system in similar regard as species in natural systems.
Trophic interactions and their implications
Herbivory, parasitism, or predation are all examples of trophic interactions that can vary geographically, seasonally, and across individual species. Despite widespread alterations, focal species within agricultural systems remain susceptible to such trophic interactions.
For instance, crops are often affected by bottom-up effects (from their interactions with microbes and fungi) and top-down effects (from insects and birds) as well as from the same trophic level (competing plant species). Such interactions reveal how a crop species may be affected by a range of factors beyond human intervention despite the use of herbicides, fungicides, or pest control management.
Nevertheless, it is crucial to understand agricultural systems still incorporate natural dynamics despite being altered considerably. Indeed, strategies of pest management often lead to unpredictable impacts, as documented by Chinese researchers in a study from 2019, which revealed that despite a general decreasing trend, macroinvertebrate communities respond variably to an agricultural disturbance with complex changes in functional richness. This complexity in response is commonly observed across systems and may affect the effectiveness of policies aiming to improve crop production.
Value of trophic dynamics within a system
The accumulation of trophic interactions, also referred to as trophic dynamics, therefore maintains the effective functioning of agricultural and natural systems. Accordingly, it is crucial to understand how changes in trophic dynamics may affect individual species to establish effective agricultural practices.
Indeed, a reduction in activity or complete removal of a species may negatively impact a range of other species including crops or livestock.
This is particularly noticeable when considering the role of microbes, which are essential to maintain crop productivity, and are commonly enhanced through the use of fertilizers. Harnessing the positive interaction between microbes and crops can therefore be perceived as beneficial to the overall system.
Other instances of managing trophic interactions include the purposeful introduction of predators to control harmful pest species. This strategy of biocontrol can be easily achieved in many environments and avoids any damage to the crop type as documented in a 2004 study using the combination of ladybirds and parasitic wasps to control aphid populations in greenhouses.
Exploiting the positive interactions between species, therefore, represents a promising strategy for agricultural practices aiming to establish successful sustainable practices as it can also reduce the need for pesticide use and extensive crop management.
Trophic dynamics in future agricultural systems
Despite the beneficial implications of managing trophic dynamics, agricultural practices are expected to experience a variety of emerging issues looking into the future from rapid reductions in available land to unprecedented environmental changes on a global scale.
Contemporary agricultural systems are already facing major concerns as soil degradation and erosion have resulted in an estimated 40% of global agricultural land being seriously degraded as reported by the UN. Regions such as Central America are witnessing even worse impacts, with 75% of the available land being infertile.
Such changes are in part driven by the destabilization of trophic dynamics, as soil degradation translated into crops being no longer supported by healthy microbial populations and suffer from increased damage of pests and pathogens.
Widespread alterations are expected to continue, as the global rise of temperatures is expected to alter microbial activity, change the geographic range of both beneficial and harmful species, and ultimately affect the stability of agricultural systems.
Trophic effects are therefore expected to undergo extensive changes, and the accurate assessment of such changes is necessary to anticipate the impacts they may generate. Ultimately, many benefits can be derived from harnessing trophic interactions, but the contrary is also true, with unpredictable changes having the potential to negatively impact crop development.
Sources
- FAOSTAT. (2020, May 7). Food and Agriculture Organization of the United Nations. http://www.fao.org/sustainability/news/detail/en/c/1274219/#:%7E:text=Globally%20agricultural%20land%20area%20is,and%20pastures)%20for%20grazing%20livestock.
- Snyder, W. E., Ballard, S. N., Yang, S., Clevenger, G. M., Miller, T. D., Ahn, J. J., Hatten, T. D., & Berryman, A. A. (2004). Complementary biocontrol of aphids by the ladybird beetle Harmonia axyridis and the parasitoid Aphelinus asychis on greenhouse roses. Biological Control, 30(2), 229–235. doi:10.1016/j.biocontrol.2004.01.012
- Taylor, R., Herms, D., Cardina, J., & Moore, R. (2018). Climate Change and Pest Management: Unanticipated Consequences of Trophic Dislocation. Agronomy, 8(1), 7. doi:10.3390/agronomy8010007
- Wang, L., Gao, Y., Han, B.-P., Fan, H., & Yang, H. (2019). The impacts of agriculture on macroinvertebrate communities: From structural changes to functional changes in Asia’s cold region streams. Science of The Total Environment, 676, 155–164. doi:10.1016/j.scitotenv.2019.04.272