Including parasites in food webs

doi:10.1016/j.pt.2008.11.003

Trends in Parasitology

Volume 25, Issue 2, February 2009, Pages 55-57

https://doi.org/10.1016/j.pt.2008.11.003 Get rights and content

Growing evidence indicates parasite inclusion in food-web analyses is a logical default. Comparisons of food webs including and excluding host–parasite interactions demonstrate the influence of parasites on community dynamics. Although including parasites is undoubtedly informative, the necessary level of detail exists for only a handful of systems. In a recent Ecology Letters article, Lafferty et al. pose many good questions to catalyze discussions for determining when and how parasites should be incorporated into food-web analyses.

Section snippets

The case for the inclusion of parasites

Here's an interesting thought experiment: which activity did more to propel humans to the top of all natural food webs, the removal or extinction of top predators through direct hunting and habitat modification or the advent of the cooking of meat for human consumption? Conventional wisdom would indicate the removal of predators is of utmost importance. However, Lafferty et al. [1] would probably contend that by eliminating food-borne parasites, cooking meat was equally influential and has been

Does parasite inclusion change food-web dynamics?

It seems well accepted that parasites change descriptive parameters, such as connectance, looping and linkage density, of food webs 6, 11, 16. However, from a broader perspective, the more challenging yet important question might be to address whether incorporating parasites changes emergent properties and dynamics of food webs such as energy flow, stability and mass balance. Several theoretical studies have indicated such properties might be altered once parasites are incorporated in food

What does adding parasites entail? What are the obstacles?

Given the increasing evidence for parasite abundance in systems and thus their warranted inclusion in food webs, what are the ramifications for web construction, analysis and interpretation? Recently, there has been a trend to add more realism to food webs – including cannibalism, ominivory and intraguild predation and now, parasites. However, although such realism is beneficial for thorough understanding of systems, the cost of all these additions is increasing complexity. However, there are

Concluding remarks

Lafferty et al. [1] and a few previous related studies 6, 7, 10, 11 collectively make a strong case that incorporating parasites into food webs should be standard procedure in the future. Determining when parasite inclusion is prudent must surely depend on the questions being asked, but given the ubiquitous effects of parasites, surely one omits them at his or her peril. However, how we go about inclusion is hard to say because we are in the early stages of wholesale incorporation, and the

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Cited by (38)

Mineral licks as a potential nidus for parasite transmission
2023, Food Webs
Discrete landscape features can concentrate animals in time and space, leading to non-random interspecific encounters. These encounters have implications for predator-prey interactions, habitat selection, intraspecific competition, and transmission of parasites and other pathogens. The lifecycle of the parasitic nematode Parelaphostrongylus tenuis requires an intermediate host of a terrestrial gastropod. Natural hosts of P. tenuis are white-tailed deer, and an aberrant host of conservation concern is moose, which are susceptible to high levels of mortality as a naive host to the parasite. Intermediate hosts become infected when P. tenuis larvae are shed in deer feces, then consumed or enter the gastropod through the foot. Incidental (or perhaps intentional) ingestion of infected gastropod intermediate hosts by aberrant or dead-end hosts often results in mortality of that animal. We present photographic evidence depicting a potential mechanism for transmission from infected white-tailed deer to moose, heretofore not examined in the literature. We deployed remote cameras at mineral licks around Grand Portage Indian Reservation in northeastern Minnesota, USA. We observed white-tailed deer defecating at mineral lick sites and geophagous moose at the same sites. We hypothesize that mineral licks may act as a nidus for P. tenuis transmission between deer and moose in this system and call for further research into the potential role of mineral licks in parasite transmission.
The Grand Portage Band of Lake Superior Chippewa is a federally recognized Indian tribe in extreme northeastern Minnesota, USA, and proudly exercises its rights to food sovereignty through subsistence hunting and fishing. Mooz (Moose) are a primary subsistence food used by the Anishinaabeg (people) of Grand Portage Band historically and presently. Management for and research on maintaining this moose population as a vital subsistence species thus sets the context for this paper examining potential for disease transmission between white-tailed deer and moose through shared use of mineral licks.
Smart carnivores think twice: Red fox delays scavenging on conspecific carcasses to reduce parasite risk
2021, Applied Animal Behaviour Science
The recent SARS-CoV-2 epidemic has highlighted the need to prevent emerging and re-emerging diseases, which means that we must approach the study of diseases from a One Health perspective. The study of pathogen transmission in wildlife is challenging, but it is unquestionably key to understand how epidemiological interactions occur at the wildlife-domestic-human interface. In this context, studying parasite avoidance behaviours may provide essential insights on parasite transmission, host-parasite coevolution, and energy flow through food-webs. However, the strategies of avoiding trophically transmitted parasites in mammalian carnivores have received little scientific attention. Here, we explore the behaviour of red foxes (Vulpes vulpes) and other mammalian carnivores at conspecific and heterospecific carnivore carcasses using videos recorded by camera traps. We aim to determine 1) the factors influencing the probability of foxes to practice cannibalism, and 2) whether the scavenging behaviour of foxes differ when facing conspecific vs. heterospecific carcasses. We found that red foxes were generally reluctant to consume mesocarnivore carrion, especially of conspecifics. When recorded, consumption by foxes was delayed several days (heterospecific carcasses) or weeks (conspecific carcasses) after carcass detection. Other mammalian scavengers showed a similar pattern. Also, meat-borne parasite transmission from wild carnivore carcasses to domestic dogs and cats was highly unlikely. Our findings challenge the widespread assumption that cannibalistic or intra-specific scavenging is a major transmission route for Trichinella spp. and other meat-borne parasites, especially for the red fox. Overall, our results suggest that the feeding decisions of scavengers are probably shaped by two main contrasting forces, namely the nutritional reward provided by carrion of phylogenetically similar species and the risk of acquiring meat-borne parasites shared with these species. This study illustrates how the detailed monitoring of carnivore behaviour is essential to assess the epidemiological role of these hosts in the maintenance and dispersion of parasites of public and animal health relevance.
Plastic density as a key factor in the presence of microplastic in the gastrointestinal tract of commercial fishes from Campeche Bay, Mexico
2020, Environmental Pollution
Citation Excerpt :
However, extensive studies for searching MPs in preys (i.e., gastropods, crustaceans, fish, etc.) of the present fish species studied are urgently necessary to have a more comprehensive knowledge of biomagnification. The present study provides a baseline as an integrative tool to other disciplines such as fish parasitology and the study of stable isotopes in order to elucidate trophic interactions based on prey consumed by predators (i.e., fishes) and the use of habitat (Byers, 2009; Lafferty et al., 2008; Juárez-Camargo et al., 2020). While pelagic species show to have ingested more particles of microplastics (i.e., H. plumierii followed by L. griseus), demersal or benthic feeders evidenced the lowest amount of these particles, i.e, C. campechanus (Fig. 2).
Microplastics (MPs) are currently one of the primary marine pollution problems around the world. MPs are distributed throughout the water column, dependent mainly on the density that is given by the polymer type, as well as the location, depth, and velocities of the water flows. This situation allows all aquatic organisms to be exposed to MPs. Furthermore, toxic substances can adhere to the MPs, making the consumption of fish with MPs a risk to human health. The aim of this study was to evaluate and characterize the microplastics present in the gastrointestinal tract of six species of fish which had the highest human consumption in Campeche, Mexico and their relationship with the density of MPs founded. A total of 316 microplastic particles from 240 individuals were found with 1.31 ± 2.59 of microplastics per fish. The results indicate that there are differences (KW–H = 53.14) between the densities of the MPs present in demersal fish (1.41 ± 0.4 g cm⁻³) with respect to the pelagic species (1.04 ± 0.24 g cm⁻³). Likewise, differences were found between fibers, fragments, and pellets present in the studied fish with a pelagic: demersal ratio of 1: 2.4 for all microplastics. The demersal species Haemulon plumierii (n = 40) presented the highest number of MPs with 115 items in total, 73 fibers, and 42 fragments. The results of this research show the first evidence that the density of the material from which microplastics are made play a key role determining their fate in marine fish habitats.
Geographical variability and parasitism on body size, reproduction and shell characteristics of the keyhole limpet Fissurella crassa (Mollusca: Vetigastropoda)
2020, Marine Environmental Research
Environmental variation may alter biological interactions and their ecological consequences. For instance, in marine ecosystems hosts and parasites are subject to environmental variability across latitudinal gradients, and their co-evolutionary dynamics may be the result of the interplay with local physical-chemical variables in seawater. Thus, assessing the environmental conditions required for a host in order to improve their survival is essential to understand the host-parasite interaction and dynamics. In this study, we evaluated the impact of parasitism by Proctoeces humboldti on the body size and reproduction of the intertidal keyhole limpet Fissurella crassa collected from three populations spanning ca. 1500 km along the latitudinal gradient of the Chilean coast. In addition, for the first time, we explore whether the effect of parasitism can be extended to changes in the organic composition and mechanical properties of the host shell. Our results show that parasitism prevalence and intensity, and body size of F. crassa increased in central Chile (ca. 33°S). Unlike body size, which was greater in parasitized limpets than in non-parasitized limpets at the three study sites, reproductive performance followed this trend only in central Chile populations, with no differences between parasitized and non-parasitized limpets collected in the northern Chilean (ca. 23°S), and lower in parasitized than non-parasitized individuals from the south-central Chile (ca. 37°S). The organic composition of F. crassa shells showed significant differences between parasite conditions (e.g. polysaccharides and water decreased in parasitized limpets) and across sites (e.g. proteins levels increase in shell of parasitized limpets from central Chile, but decreased at south-central Chile). However, variability in shell mechanical properties (e.g. toughness and elastic module) do not showed significant differences across sites and parasitism condition. These results suggest the interplay of both parasitism and environmental fluctuations upon the reproductive performance and morphology of the host. In addition, our result highlight that the host may also trade-offs reproduction, growth and shell organic composition to maintain the shell functionality (e.g. protection for mechanical forces and durophagous predators).
Host feeding ecology and trophic position significantly influence isotopic discrimination between a generalist ectoparasite and its hosts: Implications for parasite-host trophic studies
2018, Food Webs
Despite being one of the most prevalent forms of consumerism in ecological communities, parasitism has largely been excluded from food-web models. Stable isotope analysis of consumers and their diets has been widely used in the study of food webs for decades. However, the amount of information regarding parasite stable isotope ecology is limited, restricting the ability of ecologists to use stable isotope analysis to study parasites in food webs. This study took advantage of distinct differences in the feeding ecology and trophic position of different species of fish known to host the same common micropredatory gnathiid isopod to study the effects of host stable isotope ecology on that of the associated micropredator. Blood engorged juvenile gnathiids were in most cases indistinguishable from their hosts' blood, but significant isotope discrimination was observed for adults. Males were generally lower in δ¹³C and δ¹⁵N than host blood whereas host-specific isotopic discrimination for females varied among the different host species. Model predictions indicated that there is a significant effect of host blood isotope ratios on the rate of carbon and nitrogen isotopic discrimination between gnathiids and their host’s blood. As such, general differences in the feeding ecology and trophic positions of the different host species were reflected in their associated gnathiids, indicating that stable isotope analysis of gnathiids can provide significant details concerning previous hosts. The results presented herein have significant implications for how stable isotopes may be used as a tool to study the trophic dynamics and feeding ecology of gnathiids.
Factors affecting the prevalence of the trematode parasite Echinostephilla patellae (Lebour, 1911) in the limpet Patella vulgata (L.)
2017, Journal of Experimental Marine Biology and Ecology
Parasites are ubiquitous throughout nature and can have dramatic effects on their hosts. Although much is known about the pathology of parasites, the environmental factors influencing the distribution and abundance of parasites are poorly understood. Investigations into these factors could help predict the effect of parasites on the functioning of ecosystems. The limpet Patella vulgata is a key grazer on European rocky shores and is the first intermediate host for the trematode parasite, Echinostephilla patellae. This study investigated the spatial distribution of E. patellae in relation to P. vulgata at fourteen rocky shores around Ireland. Despite P. vulgata recruiting into rock pools, adults are more abundant on emergent rock and experience greater mortality in pools compared to emergent rock. It has been suggested that greater parasite prevalence in pools may be a factor driving this disjunct distribution pattern. Prevalence of infection was compared among rock and pool habitats. Size and sex of the host were also investigated in order to determine whether host phenotype influenced levels of infection prevalence. Results varied considerably among study sites, probably due to the heterogeneity of environmental conditions. No clear pattern emerged in relation to infection prevalence between habitats but this may be owing to the low numbers of limpets collected from pools. There was a significant positive relationship between infection prevalence and increasing host size. Individuals for which sex was indeterminate were more likely to be infected than distinct males or females, suggesting that infection may be causing castration and subsequent removal of these individuals from the breeding population. We discuss the importance of considering host-parasite dynamics in a period of rapid environmental change.

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Trends in Parasitology

UpdateResearch FocusIncluding parasites in food webs

Section snippets

The case for the inclusion of parasites

Does parasite inclusion change food-web dynamics?

What does adding parasites entail? What are the obstacles?

Concluding remarks

Trends Ecol. Evol.

Int. J. Parasitol.

Trends Ecol. Evol.

Ecol. Modell.

Int. J. Parasitol.

Parasites in food webs: the ultimate missing links

Ecol. Lett.

Weak trophic interactions and the balance of nature

Nature

Food web complexity and species diversity

Am. Nat.

Trophic structure and productivity of Silver Springs, Florida

Ecol. Monogr.

Community structure, population control, and competition

Am. Nat.

Parasites and food web patterns

J. Anim. Ecol.

Parasitism, community structure and biodiversity in intertidal ecosystems

Parasitology

Update
Research Focus
Including parasites in food webs