Scavenging as a Trophic Interaction

Scavenging, like carnivory, involves the act of consuming the flesh of dead animals - carrion. Technically, however, scavenging differs from carnivory in that it does not actively involve killing animals. Scavengers also differ from decomposers. Decomposers like bacteria and fungi break down the protein of dead animals into its constituent carbon-, nitrogen-, and hydrogen-based elements (Figure 1). Those elements are then broken down further into mineralized form to be taken up later by plants. Scavengers, on the other hand, consume organismal protein and convert it into their own body tissue (Figure 1 ).

Research has shown that many organisms die from sources other than predation. Although the exact value varies among species and sizes of prey, predation accounts for between 2% and 75% of organism losses annually, thus leaving 25-98% to be scavenged. In the Serengeti alone, the annual amount available to scavengers is estimated to be on the order of 26 million kg. Clearly, neither the Serengeti plains, nor any other location globally, is littered with dead animal carcasses, testimony to the magnitude of this trophic interaction. Depending on the size and species of carrion, a carcass can be despatched within hours to days. Research has also shown that scavenging efficiency, defined as the proportion of a carcass that was consumed within this time frame, averages 75%, a value that rivals the efficiencies of carnivores consuming their hunted prey.

Scavenging can be temperature dependent because of interplay between microbial decomposition and chemical detection of carcasses. This interplay leads to intermediate, optimal temperatures for scavenging, especially within temperature regions of the globe. Decomposers alone are rarely able to utilize entire carcasses. So, to avoid competition with scavengers, decomposers have evolved capacities to produce noxious and odorous chemicals that can make the entire carcass distasteful or even toxic. At moderate temperatures (e.g., 10-15 °C) microbial decomposition is at a level that produces modest concentration of chemicals leading to putrid odors that signal the location of edible carrion to scavengers. Indeed, experimental studies have demonstrated that under such conditions scavengers can find and begin to remove carrion within minutes to hours after becoming available. Higher temperatures and associated higher rates of decomposition lead to higher

Figure 1 In many systems, including the example of wolves preying on elk, predation accounts for 2-75% of losses of individual prey annually (denoted by thin arrow from the elk carcass to wolves). The remaining 25-98% of all individuals that die annual succumb to nonpredation causes. Much of this abundant carrion can be broken down into constituent chemical elements by decomposers (denoted by thick arrow from elk carcass to the decomposed organic matter pool) if scavengers are absent. In many cases, however, it is redirected to bolster populations of a diversity of scavenger species, including turkey vultures, coyotes, ravens, and foxes (denoted by thick arrow from elk carcass to scavengers and thin arrows to decomposed organic pool). Hence, scavengers compete with decomposers for carrion. Scavengers, however, are often more efficient than decomposers at despatching carrion.

Figure 1 In many systems, including the example of wolves preying on elk, predation accounts for 2-75% of losses of individual prey annually (denoted by thin arrow from the elk carcass to wolves). The remaining 25-98% of all individuals that die annual succumb to nonpredation causes. Much of this abundant carrion can be broken down into constituent chemical elements by decomposers (denoted by thick arrow from elk carcass to the decomposed organic matter pool) if scavengers are absent. In many cases, however, it is redirected to bolster populations of a diversity of scavenger species, including turkey vultures, coyotes, ravens, and foxes (denoted by thick arrow from elk carcass to scavengers and thin arrows to decomposed organic pool). Hence, scavengers compete with decomposers for carrion. Scavengers, however, are often more efficient than decomposers at despatching carrion.

concentrations of toxic amines and sulfur compounds that signal to scavengers that the item is inedible. Lower temperatures are less favorable for microbial activity and accordingly there is little or no production of chemical odors. Scavenging may thus be limited at low temperatures because, without the chemical cues, scavengers may have difficulty finding a potentially edible carcass.

Was this article helpful?

0 0
Oplan Termites

Oplan Termites

You Might Start Missing Your Termites After Kickin'em Out. After All, They Have Been Your Roommates For Quite A While. Enraged With How The Termites Have Eaten Up Your Antique Furniture? Can't Wait To Have Them Exterminated Completely From The Face Of The Earth? Fret Not. We Will Tell You How To Get Rid Of Them From Your House At Least. If Not From The Face The Earth.

Get My Free Ebook


Post a comment