Chemically Mediated Competition Between Microbes and Animals: Microbes as Consumers in Food Webs

Abstract

Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.

Effects of Time of Day and Activity Status on Bobcat (Lynx rufus) Cover-Type Selection in Southwestern Georgia

“…DeVault et al 2011). In addition, increased time allows for carcass degradation by insects or microbes (DeVault et al 2004, Burkepile et al 2006, reducing the ability to distinguish prey that was killed vs scavenged. Maximum time from cluster formation to investigation in our study was 24.6 days.…”

“…In addition, given that increased elapsed time since cluster formation to investigation increases the likelihood that prey will be entirely consumed (e.g. DeVault et al 2011) or degraded by insects (DeVault et al 2004, Burkepile et al 2006, we hypothesized that the probability of detecting kill sites would increase with reduced time from cluster formation (i.e. presumed time of predation) to investigation.…”

Animals in a bacterial world, a new imperative for the life sciences

“…Similarly, the acquisition of an appropriate microbiome at critical life history stages of many animals affects their subsequent behavioral patterns and thus the stability of their ecological roles in their communities (64). Bacteria feeding on dead animals in the sea, and likely on land, repel animal scavengers by producing noxious metabolites; these products allow the bacteria to effectively outcompete organisms 10,000 times their size (111).…”

Ecological studies on the decomposition rate of fish carcasses by benthic organisms in the littoral zone of Lake Constance, Germany

“…Beggiatoa is known to produce chemicals that repel scavengers (Kim et al, 2007). Also, Burkepile et al (2006) showed that microbe-laden carrion was four times more likely to be uncolonised by megafaunal scavengers than was fresh carrion. The bacteria on the carcasses produce toxic chemicals that discourage scavengers.…”

“…The bacteria on the carcasses produce toxic chemicals that discourage scavengers. Thus, bacteria compete with scavengers by rendering carcasses chemically unattractive (Burkepile et al, 2006).…”