Experimental evidence for fundamental, and not realized, niche partitioning in a plant–herbivore community interaction network

Abstract

Summary1. Patterns of niche partitioning can result from local ecological interactions (e.g. interspecific competition) occurring within a contemporary time frame (realized niche partitioning). Alternatively, they may represent the end product of historical processes acting over long time frames (fundamental niche partitioning). 2. Niche partitioning is often detected by analysing patterns of resource use within communities, but experiments are rarely conducted to test whether patterns of non-overlapping resource use reflect realized or fundamental niche partitioning. 3. We studied a community of restio leafhoppers from the genus Cephalelus and their host plants, the Restionaceae (restios). We used network and experimental approaches to determine whether network modularity (a measure of niche partitioning within local communities) reflects fundamental or realized niche partitioning. Using a weighted modularity index for two party networks (e.g. insect-plant), we determined whether the network of this community is modular (i.e. consists of groups of species interacting strongly, with weak interactions between groups). We also aimed to identify specific Cephalelus -restio modules (groups). Using knowledge of module membership to design experiments, we tested whether Cephalelus species from two different modules, Cephalelus uncinatus and Cephalelus pickeri, prefer and perform better on restios from their own modules vs. restios from other modules. These experiments were performed under controlled conditions, eliminating the influences of competition and predation on host choices. 4. The Cephalelus -restio community was modular, implying niche partitioning. Cephalelus also preferred and performed better on restios from their own modules in the absence of local contemporary factors. Most niche partitioning in the investigated Cephalelus community is not caused by local interactions, and thus, host use patterns represent fundamental niches. Our findings highlight the importance of understanding local community structure in the light of processes extrinsic to the local community context.

Significant Local-Scale Plant-Insect Species Richness Relationship Independent of Abiotic Effects in the Temperate Cape Floristic Region Biodiversity Hotspot

“…Instead, the fact that the relationship holds across communities with very similar climates, and after accounting for the influence of post-fire vegetation age, elevation, and other aspects of vegetation structure, suggests that it likely arises as a result of specialisation of restio associated insects at taxonomic levels below the plant family level. This mechanism is supported by studies of host-use and preference in restio associated leafhoppers [19,41]. Our results are also similar to those of the handful of other studies in the CFR which have investigated plant-insect diversity linkage, but have sampled across whole plant communities [27,28,30,43], perhaps suggesting that narrow specialisation might be widespread in herbivorous CFR insects.…”

“…Alternately, insects may be specialised on a plant species and only be present in the community when nutrient uptake from that plant species is optimal. Leafhopper species in the tribe Cephalelini (Cicadellidae) have been shown to be specialised on Restionaceae taxa [19,39–41], whereas Betiscoides grasshoppers are specialised on the Restionaceae at the family level [42]. …”

Spatial turnover in host-plant availability drives host-associated divergence in a South African leafhopper (Cephalelus uncinatus)

“…Another divergent selection pressure that might cause immigrant inviability is plant physiology. We previously showed that C. uncinatus adults using H. aristatus have reduced survival on Elegia filacea , a lower ranking host species [41]. It is therefore conceivable that reproductive isolation is, in addition to e.g.…”

“…C. uncinatus uses several genera of restios from the Willdenowieae sub tribe, as well as several species in the genus Elegia which belongs to the Restioneae sub tribe [39]. Augustyn et al [41] demonstrated experimentally that C. uncinatus from a single site actively chooses its predominant field host and also survives better on it than on unused restio species. As experiments were performed in the absence of predators, the authors suggest that preference is linked to performance through plant chemistry.…”

“…He reported consistent, but slight differences in genitalia between populations using Willdenowia incurvata , Mastersiella digitata and Elegia nuda as host-plants (species that differ in culm thickness and leaf sheath colour). Since competition appears to be an unlikely driver of host-shifts in restio leafhoppers [41, 42], we determine whether spatial heterogeneity in plant distributions could have initiated host-shifts in C. uncinatus . If so, we expect to find: (1) that host-plant distributions are smaller than the distribution of C. uncinatus , thus generating a geographic mosaic in the availability of different hosts across the insect species range, and (2) that host preference, colour and shape of restio leafhoppers are locally adapted to their host-plants across this geographic mosaic.…”