Specific parasites indirectly influence niche occupation of non-hosts community members

Abstract

The coexistence of phylogenetically related species is an attractive topic because of the potentially intense interspecific competition. The most often investigated mechanisms mediating coexistence of these species are environmental filtering and niche partitioning. However, the role of other factors, such as species-specific parasites, is still poorly understood. Along the riparian understory of a tropical forest, we explored niche occupation and coexistence between Chrysso intervales and Helvibis longicauda, two related syntopic web-building spiders. We also investigated the effect of H. longicauda mortality induced by a specific fungus parasite, Gibellula pulchra, on the dynamic of C. intervales spatial distribution. Coexistence was mediated mainly by a fine-scale horizontal spatial segregation. H. longicauda built webs almost exclusively close to the river, while C. intervales occupied adjacent areas (10-20 m away from margins). We also found differentiation in other niche dimensions that might allow coexistence, such as in plants occupied, height of web placement, width of leaves used for thread attachment and phenology. H. longicauda mortality caused by fungi was higher during winter than in summer. Consequently, the abundance of C. intervales increased at distances close to the river, indicating competitive release through a density-mediated indirect effect. This demonstrates how non-competitive specific-antagonists can indirectly affect other non-hosts competing community members and influence their spatial distribution in fine-scale ranges. We suggest that environmental filtering restricts H. longicauda to cooler regions; niche partitioning leads populations to occupy different vertical strata and competitive exclusion precludes C. intervales to reach river margins, generating an unusual horizontal zonation pattern.

Spiders follow an ideal free distribution based on traits of the plant community

“…We also counted/identified the number of potential (suitable) sites existing under 3 m height (the range of occurrence height of spiders) within transects. A site was considered suitable when the plant species had (i) broadleaves (leaf or leaflet), (ii) had a potential point underneath (a branch, another leaf/leaflet or the curvature of the leaf itself) to allow spiders' attachment of threads (Gonzaga et al ., 2006), and (iii) had more than 4 cm width and (iv) less than 25% of estimated area loss due to herbivory (Cardoso et al ., 2018) (Fig. 1b–d).…”

“…Along the margins of the Mirante river (Fig. 1a), we established 15 parallel transects (10 m length × 2 m width each) at three distances, 0, 10, and 20 m, from the riverbank (five transects each) (see details in Cardoso et al ., 2018). The area is dominated by two tangle web weaver spiders that rest underneath leaves: Chrysso intervales Gonzaga, Leiner & Santos, 2006 (Theridiidae) (Fig.…”

“…The niche occupation of these species was investigated previously in Cardoso et al . (2018). On each transect, we counted the number of spiders and recorded the identity of the plant they were occupying.…”

“…On each transect, we collected additional data of: georeferencing, environment luminosity (canopy cover), temperature and humidity (see further details of data collection in Cardoso et al . (2018) and the respective Online Resource 1).…”

Niche partitioning and coexistence of two spiders of the genus Peucetia (Araneae, Oxyopidae) inhabiting Trichogoniopsis adenantha plants (Asterales, Asteraceae)

“…Partitioning of resources among spiders is generally explained by: (1) variation in prey types or sizes as a consequence of different hunting strategies or body size[31–34] reducing interspecific competition and allowing coexistence among species; (2) activity time, with different species varying in phenologies or circadian cycles [34–36] resulting in different population densities of the species throughout the year which reduces interspecific competition; (3) use of space, with different species using different microhabitats as the result of cryptic colorations [37], different foraging behaviors or different sites chosen for the placement of webs (e.g., different heights) [38–42], physiological tolerance [11,43] or based on thermal preference in a gradient of environmental characteristics in cave-dwelling spiders [44–45]. (4) Indirect influence of a species-specific fungus parasite, where the intensity of competition for space is reduced when the dominant host species is highly affected by the parasite and allows the colonization of other less dominant species [46]. (5) Predation, when agonistic interactions (e.g.…”