An entomocentric view of the Janzen–Connell hypothesis

• DOI: 10.1111/icad.12337
• Publication Date: 2019-01-03T05:06:50Z
• Authors: Yves Basset; Scott E. Miller; Sofia Gripenberg; Richard Ctvrtecka; Chris Dahl; Simon R. Leather; Raphael K. Didham
• Keywords: Entomology; Conservation Biology

In 1987, in the first issue of Conservation Biology, Edward O. Wilson wrote about "little things that run world" – importance and conservation insects (Wilson, 1987). Readers Insect Diversity will no doubt be very familiar with concept. Sadly, however, this perception is not as widely shared among rest scientific community it should be, are still comparatively neglected a prime focus investigations. For instance, if we look at Thompson-Reuter impact factors (IF) specialised journals for 2017 (http://jcr.incites.thomsonreuters.com/JCRJournalHomeAction.action?year=&edition=&journal=#), highest ranked journal dedicated to entomology, Annual Review Entomology (IF = 13.860), 139th out 122 271 journals. comparison, our botanical colleagues fare somewhat better, plant sciences, Plant Biology 18.172), 83rd overall. continues top entomology 2.091; 14th), but overall 4549th evaluated by Thompson-Reuter. There certainly room improvement, course, general reflects large difference scale endeavour across different disciplines. Part challenge may related an imbalance ratio funding afforded invertebrate studies (Leather, 2009). We entomologists acutely aware inherent biases research. Vertebrate dominate field (69% papers versus 3% described species) while lag far behind (11% 79% species: Clark & May, 2002). This taxonomic chauvinism has been commented on lamented upon many times (e.g. Leather, 2009 references therein), including one previous editorials (Leather et al., 2008). Moreover, current trends show signs improvement (Titley 2017), against insect becoming even more pronounced tropical countries where recent estimates suggest over 25 000 arthropod species occurring just few hectares rainforest (Basset 2012). But these issues most serious cause concern. argue here neglect study organisms led bias understanding functional ecology ecosystems. other words, ignorance identity role ecosystems seriously impede conclusions true contribution make ecosystem functionality (Weisser Siemann, able estimate indirectly ecological processes, without good knowledge life history responsible rather subjective. "Knowing players" therefore crucial sound effects functioning (Schmitz, situation particularly obvious insect-plant interactions (or say instance "plant-insect interactions"?), which represent significant research its own right (Calatayud 2018). Many science researchers simply seem ignore diversity types doing work. given difficulty evaluating damage caused sap-sucking insects, herbivory (leaf damage) only action leaf-chewing insects. evident carried forests Coley Barone, 1996). Nevertheless, detailed have shown occurrence plants means trivial (Novotny Basset, 1998; Dem 2013). Since can vectors important diseases (Denno Perfect, 2012), they could effect rates mortality their hosts. addition, "plant-insect" literature focused feeding leaves. Much less known identities roles attacking parts (e.g., flowers, fruits, roots, stems). Another estimation rainforests. Botanists keen measure area holes leaves (review 1996) few, any, discuss interpretation findings regard histories main leaf damage. Total often assumed correlated richness, abundance or biomass Coley, 1983, discussing spatial distribution herbivory). The handful have, considered associated variables (abundance, biomass) all concluded likely depend behaviour dominant complicate results obtained focusing community-level patterns Marquis, 1991; Basset Höft, 1994). know major herbivores plants, rainforests, driven relatively species, because rare restricted time (Owen, 1983; Bernays Graham, 1988). Thus, correlate fitness, gives us clues preferences essay, briefly explore implications ignoring traits context another topic popular colleagues, Janzen–Connell hypothesis, JCH (Janzen, 1970; Connell, 1971). proposes explanation coexistence tree diverse forests. Seeds disperse sites close parent trees, also frequently attacked host-specific enemies such pathogens might aggregate near trees. By contrast, seeds seedlings do manage further away from survive due escape enemies. conspecific negative density-dependent survival proliferation species-specific hosts areas high densities, giving correlation between relative pest attack rate distance trees nearby offspring 1971; Comita 2010; Bagchi 2014). seminal paper Janzen (1970), examples density dependence provided, information gathered subsequent papers, along (Table 1). Most concerned pay little attention potentially induce (reviews Clark, 1984; Hammond Brown, Carson 2008; 2014: 63 considered). compilation Table 1 indicates assessed specific causing consistent predictions were performed Neotropics (only originated Old World tropics), open forests, savanna pastures, targeted seedlings, included palm leguminous (64% cases) bruchine beetles. One tempted think systems perhaps selected ease studying seed crops noticeable predators. What clear, targeting closed tall families urgently needed before sweeping generality induced specifically listed almost exclusive chewing either seedlings. exception influential he reports external-feeding bug Sterculia apetala 1972a). Seed bugs (Lygaeidae families) renowned predators tropics (Slater, 1972 therein). Hence, clear potential imperative guild externally seed- fruit-sucking Janzen's seed-sucking illustrates point. studied transmit pathogenic fungus host 1972a), ultimate appear pathogen than insect. need consider synergy pathogens. As discussed al. (2008), ultimately reported single species. While within framework mostly conducted already dispersed mother plant, (1970) suggested promoted pre-dispersal (i.e., developing mature canopy). Gripenberg (2018), stressing enemies, reviewed pattern predation forest communities. To date, includes 15 world-wide, two thirds provide hard data Again, currently available so limited lack necessary background adequately gain knowing negative-density rainforests? Primarily use (specificity) species; whether same tend feed adult foliage seedlings; foraging address some briefly, separate rainforests highly 1980; Ctvrtecka 2014; Gripenberg, 2018), accordance expectations JCH. well degree contagion considered. example, (1975b) beetles Guazuma ulmifolia Costa Rica, being predator tree, exclusively attacks after fallen ground. fully understand pre- post-dispersal any resulting fitness recruitment. Even assumptions specificity met, does imply pervasive. Insects subsist minimum densities order mortality. New Guinea 95% woody sampled seed-eating weevil lepidopteran assemblages had low infestation (Ctvrtecka Sam 2017). Here, recognition assessing possible Overlooking higher taxa lead ambiguous results. Bruchinae Fabaceae 1980), whereas totally replaced several subfamilies fabaceaous thus much weevils World, 1. Furthermore, botanists considerable phylogeny JCH, take note explain oviposition seeds, necessarily phylogeny. fleshiness fruit (Sam 2017; 2018; C. Dahl unpubl. data). When contributions effects, insights into taxa. well-known Lepidoptera, difficult pulp eaters scavengers. Several scavengers contain lineages strategies, Tineidae (Robinson, 2009), precise identification reared fruits crucial. If now turn there community-wide Twenty years ago, Guyana free living persisted generalists, mediated were, consequently, unlikely exist system (Basset, 1999). (particularly seedlings) invalidate coexistence, generated generalist attracted (Lewis Regarding noted pastures 1), fact, presumably local 1971), rarely demonstrated. biotic abiotic conditions experienced canopy understorey strikingly different, suites free-living strata. These differences observed both level 2001) whole 2015). course exceptions involve endophagous (stem borers, gallers, miners) ectophagous external strata buffered extent microclimatic inside tissues. proportion supported gallers miners Panamanian wet was amounted 6% (out 18 Medianero 2003). Under conditions, uncommon Despite claims instances unequivocally assigned particular (Barone, 2000; Downey experience nearly impossible vast majority case greatly impedes ability investigate causal mechanisms amount categories herbivore differ continents. percentage represented 56%, 78%, 85% observations Panama, Thailand, Papua Guinea, respectively (Y. Identifying variation (at least herbivory) And, tolerate differing levels triggered question. entertain idea 2010), then effects? ground, 1980) certain Curculionidae (Pinzón-Navarro 2010) fit bill, although involved attack. underestimate ants removers (Ruzi engineers effects. Charles, 2000). Leaf-chewing Chrysomelidae, leaf-feeding (Entiminae), Lepidoptera larvae total individuals collected Orthoptera Phasmatodea infrequent, during day-time censuses incidence 1999) makes them candidates successfully exist. Further cases notoriously dangerous worth briefly. First, phytopathogens needs quantified understood. includes, xylem-feeding Cicadellinae, common nymphs adults phytopathogenic viruses (Nielson, 1968). Additionally, (for example Conotrachelus spp.) bark beetles, larval stage perform maturation situation, fungi, Dutch elm disease (Martín Second, damaging meristems threatening, erebid moth decapitating Rica 1971b). category represents 20% damaged Lepidopterous stem borers group free-feeding caterpillars, easy quantify Sullivan, Last, completely defoliate include outbreaks 2000), Large caterpillars Saturniidae (Hartnett 2012) investigating context. conclusion, via combination (Lawson understorey, possibly aggravated transmission vectors. collect identify culprits challenging, generalists specialists elusive behaviours. (1971b), estimated average 10 minutes decapitate seedling walking off, rendering direct census difficult. Elegant experiments insecticide exclusion help effectively 2014) those coupled old-fashioned natural observations, acquired new technologies. metabarcoding gut García-Robledo 2013) automatic detection activity Reynolds Riley, 2002) night, promising opportunities Further, locations extensive vegetation data, basal area, location, production available, ForestGEO network permanent plots (Anderson-Teixeira 2015; tools, DNA barcoding, assist rapid accurate (Miller, 2014), BIN clustering algorithm interim nomenclature system, facilitates forming putative concepts communicating (Schindel Miller, Ratnasingham Hebert, hope convinced non-entomologist readers, curious title value paying and, effect, collaborate entomologists. Hopefully, regular readers see better scope collaboration ecologists regarding fascinating topic. ideas advanced essay shaped project Czech Science Foundation (GAČR 16-20825S) grant US National (DEB 0841885).