To improve ecological understanding, collect infection data

Abstract

Ecologists seek to understand and predict how organisms respond to multiple interacting biotic and abiotic influences, an increasingly difficult task under anthropogenic change. Parasites are one of these biotic influences that are pervasive in natural systems and frequently interact with other stressors. Because they often have cryptic effects on their host organisms, their role in the distribution, abundance, composition, and dynamics of populations, communities, and ecosystems is easy to overlook. However, studies that neglect the role of parasitism may miss or misinterpret organismal responses to environmental change, hampering ecological predictions. We discuss case studies wherein the inclusion of parasite infection status altered the interpretation of ecological outcomes, and offer paths forward to make parasite data acquisition, analysis, and interpretation more accessible to ecologists. Given that parasites are responsive to environmental changes, timely attention to their influence on host responses is critical for accurately predicting future ecological states.

Resetting our expectations for parasites and their effects on species interactions: a meta‐analysis

“…Moreover, feedbacks between interactions are common; for example predation not only interacts with and affects competition (Chase et al, 2002 ), but the strength of competition also depends on the intensity of predation (Gurevitch et al, 2000 ; Siepielski et al, 2020 ). Yet, because the cascading effects of parasitism are rarely accounted for (Cohen et al, 1993 ; Gehman et al, 2019 ; Kuris et al, 2008 ; Marcogliese & Cone, 1997 ), we run the risk of over‐ or underestimating any direct negative effects of a focal species interaction.…”

“…We simply do not know what the emergent and general effects of parasites are on species interactions hosts experience. Moreover, studies have not traditionally considered parasites in their experimental designs and theoretical frameworks, despite many calls to do so (Cohen et al, 1993 ; Gehman et al, 2019 ; Kuris et al, 2008 ; Marcogliese & Cone, 1997 ). This is potentially problematic, because if effects of a focal interaction are exaggerated (or reduced) when a host is parasitized, and parasitism is not accounted for, the magnitude of a focal interaction may be over‐ or underestimated.…”

A global parasite conservation plan

“…Add parasite biodiversity to survey efforts for free-living species Species inventories and checklists rarely include parasites, leaving parasites both out of sight and out of mind for the scientists who survey and monitor biodiversity. Systematically collecting parasite data during free-living biodiversity surveys would help to establish current parasite biodiversity baselines, identify rare parasite species, and monitor future changes in parasite biodiversity (Gehman et al, 2019), a resource-efficient and effective way to advance parasite biodiversity conservation in spite of the (current) lack of dedicated funding. Below we note some specific opportunities and challenges for these new endeavors.…”

Parasitism shapes selection by drastically reducing host fitness and increasing host fitness variation

“…Notably, all three analyses had a high degree of heterogeneity (I 2 all > 95%; electronic supplementary material, table S1), indicating that there are substantial among study and/or species differences in responses of hosts to parasite infection that may have important ecological and evolutionary implications [28]. Indeed, although the contribution of parasitism in population ecology is increasingly recognized, many studies have not traditionally considered the effects of parasitism, despite many calls to do so [30][31][32][33]. Infection by parasites may be subtle or affect only a few individuals in a population [34,35], but as shown here those effects can be quite substantial.…”