Biodiversity and ecosystem function: the consumer connection

“Loss of a major functional group, such as apex predators, other consumers, or benthic filter-feeders, may, as previously discussed, cause drastic alterations in ecosystem functioning (Chapin et al. 1997, Duffy 2002, Jackson et al. 2001).”

“Consistent with these theoretical predictions, Duffy (2002) found that experimentally increasing grazer diversity increased grazer biomass but decreased algal biomass.”

“This limitation has been discussed at length by authors who have outlined the potential biases and incorrect conclusions that could result from using such simpli-fi ed, model systems ( Duffy, 2002 ; Duffy et al., 2007 ; Cardinale et al., 2009b ).”

“Heuristic theory has suggested that fundamental biological differences between animals and plants may produce qualitatively different impacts of diversity changes at higher vs. lower trophic levels on ecosystem properties (Duffy 2002).”

“As consumer species are under high anthropogenic pressure in many ecosystems (Duffy 2002, Myers and Worm 2003, Lotze et al. 2006), additional effects on evenness can be expected, especially as consumption strongly counteracts enhanced dominance in fertilized environments.”

“While predator diversity can enhance trophic cascades through complementarity of diets, interspecific facilitation (Sih et al. 1998; Duffy 2002), increased likelihood of keystone predators, or different behavioural responses by prey (Byrnes et al. 2006), impacts on prey may be reduced if predators…”

“…species richness (and the key fauna they support) between the AEP and IWP has never been assessed in the light of recent concepts and data on biodiversity– ecosystem function relationship and cascading effects along the food chain (e.g. Duffy, 2002; Hector & Bagchi, 2007; Naeem et al., 2012).”

“Additionally, not only stability but also ecosystem functions might be strongly mediated by the arrangement of interaction strengths (Mikola & Setälä 1998; Duffy 2002; Montoya et al .”

“It is also apparent that, at the functional group level, there are subtle differences among species that are manifest only under altered conditions or over long time periods (Yeates et al. 1999; Duffy 2002).”

“That is, species richness is inversely related to trophic level (Duffy 2002, Petchey et al. 2004a, Vinebrooke et al. 2003).”

“Although this trend may be more common for animals (Duffy 2002), it has also been observed in some plants (Duarte 2000).”

“According to the trophic cascade theory, abundance, and species composition at the top predator level affect the lower trophic levels of aquatic ecosystems via the top-down control of the community structure (Carpenter et al., 1985; Duffy, 2002).”

“Network structure is a key theme for numerous ecological topics, including ecosystem stability (May 1972; Allesina & Pascual 2007; Rooney & McCann 2012), functioning (Duffy 2002) and resilience to exploitation or species extinction (Worm & Duffy 2003; Worm et al. 2006).”

“The reason is that more diverse assemblages contain a wider range of predator-resistant taxa, such that predation shifts dominance toward resistant species (‘species turnover’, Leibold 1996) rather than reducing aggregate prey biomass as in simple food chains (Duffy 2002).”

“Indeed, with very few exceptions (e.g. Holt & Loreau 2002), trophic interactions have not been incorporated into the framework of BD-EF theory in any systematic way (Duffy 2002).”

“However, most empirical investigations have focused on diversity of primary producers; the links between consumer diversity and ecosystem function remain understudied (2, 3).”

“Mechanisms that might lead to such an effect are similar to those for sessile species discussed previously (see also Duffy 2002).”

“…are often keystone species, their impact on other biota cascading down through the ecosystem and ultimately affecting community structure and biodiversity levels, with positive effects on species numbers (Terborgh et al. 1999; Schmitz, Hambäck & Beckerman 2000; Berger et al. 2001; Duffy 2002).”

“While BEF has not developed in strict isolation from PPI (Wilby & Thomas 2002; Cardinale et al. 2003; Chalcraft & Resetarits 2003), the two research areas clearly have distinct histories and different emphases (Duffy 2002).”

“While the patterning of species interactions in real biological communities (Paine 1992; Fagan & Hurd 1994; deRuiter et al . 1995; Raffaelli & Hall 1996; Wootton 1997) affects both their stability (Yodzis 1981; McCann et al . 1998; Neutel et al . 2002) and ecosystem functioning (Hulot et al . 2000; Duffy 2002; Paine 2…”

“However, these particular attributes have complicated empirical investigations of top-down control within terrestrial food webs (Strong 1992, Holt 2000, Polis et al. 2000, Power 2000, Duffy 2002).”

“The relatively poor understanding of top-down control in terrestrial systems is, in part, due to the difficulties in experimentally manipulating some vertebrate consumers in the field and the long time scale of terrestrial vegetation responses (Duffy 2002; Gruner et al. 2008; Allen & Crawley 2011).”

“The estimation of the potential number of ecological extinctions caused by overfishing is made easier because these extinctions are typically nonrandom (83, 84).”

“Intraspecific differences in foraging or behaviour may augment overall responses to herbivore communities (Schmitz & Suttle, 2001; Duffy, 2002) or may increase functionality under the insurance hypothesis (Yachi & Loreau, 1999).”

“5 billion annually (Losey and Vaughan, 2006), is impacted by changes in natural enemy diversity may be especially important because these higher trophic level species are particularly vulnerable to extinction (Kreuss and Tscharntke, 1994; Duffy, 2002).”

“Thus, there is general recognition that incorporating consumers represents a frontier in understanding linkages between biodiversity and ecosystem function (Duffy 2002; Naeem 2002; Raffaelli et al. 2002).”

“Hence, defining functional groups is a non-trivial and sometimes controversial task (see review by Duffy 2002 ), although more quantitative methods have been explored (e.g., Petchey and Gaston 2002).”

“Indeed, marine studies have been instrumental in shifting the focus towards higher trophic levels, specifically looking at herbivory and predation (Duffy 2002, Duffy et al. 2003, Bruno and O’Connor 2005, O’Connor and Crowe 2005, Stachowicz et al. 2007, Gamfeldt and Hillebrand 2008), and how these…”

“Key words: Arbacia lixula; community changes; Diplodus sargus; Diplodus vulgaris; fishing impacts; marine reserves; Mediterranean Sea; Paracentrous lividus; species interactions; sublittoral rocky reefs; topdown control; trophic cascades.”

“For example, dietary complementarity or interspecific facilitation among predators could increase herbivore suppression (Sih et al. 1998; Duffy 2002 ).”

“In the context of such multi-trophic level systems, diversity is potentially important in two ways (Duffy 2002).”

“This lack of data means that trophic interactions are not incorporated into the current framework of biodiversity–ecosystem functioning theory (Duffy 2002, Raffaelli et al. 2002).”

“The presence and diversity of a mesograzer community are important for controlling epiphytic algae (Duffy, 2002).”

“Thus, the functional diversity of consumers and effects of consumer diversity on ecosystem processes in natural communities remain poorly understood (Duffy 2002, Balvanera et al. 2006).”

“This suggestion that food-web complexity will foil trophic cascades has become a paradigm for many ecologists, although it remains largely untested ( Duffy 2002 ).”

“Thus, our knowledge of the functional role of diversity is weakest for the groups of species that often have the largest effects and may be at greatest risk of extinction ( Duffy 2002; Raffaelli 2004).”

“Understanding how biodiversity influences ecosystem processes critically depends on our knowledge of the roles of component species (Loreau et al. 2001; Duffy 2002; Ostfeld and LoGiudice 2003).”

“The most difficult species’ benefits to assess are those occurring via trophic cascades and the so-called ‘consumer connections’, since they might be wholly unanticipated or build up unexpectedly, with far reaching consequences even in species-rich communities (Duffy, 2002; Mouillot et al., 2013; Gascon et al., 2015).”

“Theoretical and empirical research has demonstrated that complexities such as age-structured omnivory, intraguild predation and anti-consumer defenses can diminish the effects of strong ‘top-down’ forces or trophic cascades (Strong 1992, Polis & Strong 1996, Duffy 2002).”

“Particular combinations of species (sheep and cattle) with complementary feeding preferences have greater impacts on plant diversity than either herbivore species alone (Duffy 2002).”

“The litter decomposition is considered a significant process which releases carbon into the atmosphere and nutrients in such forms that can be exploited for plant and microbial production (Chapin et al. 1997; Duffy 2002).”

“decreasing the probability that any given macroalga will be well defended against all herbivores [19,20].”

“The plasticity of consumer diet and interaction strength may have a strong impact on the diversity effects on stability, as already suggested for species richness effects on biomass and productivity (Duffy 2002).”

“Thus, an obstacle for classification of functional groups is that assignment of species functional roles may differ, depending on the functional traits of interest (33, 34).”

“This is despite the fact that prey diversity might be expected to decrease the effectiveness of trophic interactions via several plausible mechanisms (Duffy 2002).”

“Unquestioned, however, is the need for additional studies that quantify the strength and routes by which indirect effects of large, mobile predators ramify through terrestrial systems (Duffy 2002, Estes 2005).”

“invertebrates can be considerably higher than in vertebrate consumers and predators (Duffy, 2002).”

“…[designs where the carrying capacity of each monoculture and each mixture are recorded are relatively tractable in a range of systems including bacteria (Gravel et al. 2011), plants (Schmid et al. 2008), insects and parasites (Tylianakis et al. 2007), plankton (Fox 2004), and animals (Duffy 2002)].”

“…et al. 2002; Loreau et al. 2002 for overviews), it is not until recently that the multitrophic effects of diversity change have been analysed (Duffy 2002; Raffaelli et al. 2002; Duffy et al. 2003; Thébault & Loreau 2003; Fox 2004; Hillebrand & Cardinale 2004; Petchey et al. 2004; Ives et…”

“It therefore remains unclear whether general effects of predator richness exist and, if so, whether they are comparable to those observed within lower trophic levels (Duffy 2002, Bruno and Cardinale 2008).”

“Second, species traits can determine the mechanisms of direct and indirect interactions (Duffy 2002; Schmitz 2007; Violle et al. 2007).”

“trophic, and also non-trophic interactions (Fig. 2; Duffy, 2002; Hines et al., 2015b; Seabloom et al., 2017; Sobral et al., 2017; Tiede et al., 2016).”

“Such trophic cascades are only expected in systems in which interaction strengths are determined by few functionally dominant species (Duffy 2002, Moksnes et al. 2008).”

“Th e observed stronger BEF relationship in primary consumers relative to primary producers has been predicted conceptually (Duff y 2002, 2003).”

“Consistent with this idea of higher sensitivity, much evidence suggests that they are usually the first to go extinct or to be seriously affected in a system after anthropogenic perturbations such as contamination (Newton, 1979; Duffy, 2002), or modification of landscape structure and composition (Chamberlain et al.”

“A species’ functional role in an ecosystem considerably depends on its dietary preference, and taxonomically unrelated species can exhibit similar ecological functions in different parts of the world (Lein, 1972; Duffy, 2002).”

“Because algal taxa vary greatly in their quality as food resources for different consumers, a diverse assemblage is more likely to contain inedible taxa that can resist many of the grazers that are likely to invade biofuel ponds (Duffy 2002).”

“Reduced functional diversity and the loss of higher trophic levels result in reduced niche use, reduced efficiency of energy use and transfer, higher leakage, and as a consequence reduced secondary productivity and biomass ( Duffy 2002 ).”

“The plasticity of consumer diet and interaction strength may strongly impact the diversity effects on both the magnitude and variation of ecosystem processes, as already suggested for species richness effects on biomass and productivity (Duffy 2002).”

“…function relationships should be examined in two orthogonal dimensions: horizontal diversity within trophic-levels and vertical trophic-level diversity within ecosystems (Duffy 2002, Paine 2002, Dyer and Letourneau 2003, Schmitz 2003, Thébault and Loreau 2003, Ives et al. 2005).”

“It constrains metabolic rates of organisms (Brown et al. 2004) and defines the functional roles and trophic interactions of species in ecosystems (Duffy 2002).”

“…functioning focused on temperate grassland communities (Naeem et al. 1994, Tilman et al. 1996), recognition that species in higher trophic levels are more vulnerable to extinction (Petchey et al. 1999, Duffy 2002) has recently shifted attention onto multi-trophic systems (e.g., Duffy et al. 2007).”

“The nature of species impacts on ecosystems can be highly dependent on their functional identity determined by their traits (Chapin et al. 1997, Duffy 2002, Chalcraft and Resetarits 2003, Hooper et al. 2005, McGill et al. 2006, Petchey and Gaston 2006, Wright et al. 2006, Violle et al. 2007).”

“Coral reefs are high-diversity systems that provide key ecosystem services such as fisheries and coastal protection (Duffy 2002).”

“Further, the functional diversity and complex trophic interactions in the food web (e.g. omnivory, intraguild predation) may affect the strength and penetrance of trophic cascades (Strong 1992; Abrams 1993; Duffy 2002; Duffy, Richardson & France 2005; Duffy et al. 2015).”

“highly resilient to intermediate levels of disturbance and then suddenly breaking down irreversibly, as suggested for trophic [55] and pollination networks [56].”

“3) is consistent with both conceptual predictions relating to greater physiological, resource, and behavioral complexity with increasing trophic level (Duffy 2002), as well as experimental evidence (Griffin et al.”

“It is possible that this marine–terrestrial difference is evidence that ecosystem production or biomass may be influenced more by herbivores or predators than by plant diversity in marine systems (Duffy 2002).”

“Only a few studies have shown how diversity of higher trophic levels affects functions performed at the base of food webs (see Duffy 2002 for a review).”

“Such heterogeneity varies among assemblages according to larger-scale divergence in the composition of regional species pools and localized fluctuations in species abundances, with potentially complex implications for biodiversity–ecosystem functioning (B–EF) relationships (Duffy 2002; Ives, Cardinale & Snyder 2005; P…”

“The services provided differ depending on the nature of the arthropod and plant communities (Duffy 2002).”