Biodiversity and ecosystem function: the consumer connection

“The range of functional traits may capture the potential for resource partitioning (Diaz and Cabido 2001, Petchey and Gaston 2006), which has been forwarded as one of the key mechanisms linking biodiversity and ecosystem functioning (Loreau 1998, Duffy 2002 ).”

“Species loss has been shown to modify food web structure due to secondary extinctions (Ebenman et al. 2004), which may lead to strong changes in ecosystem processes by altering trophic cascades (Duffy 2002).”

“More broadly, the ecological literature is replete with examples of how species loss impairs ecological function or how biodiversity in general is linked to ecological function (e.g., Anderson et al., 2011; Duffy, 2002; Estes et al., 2011; Hooper et al., 2005; Loreau et al., 2001).”

“The search for links between biodiversity and ecosystem processes has become a major theme in community ecology (Tilman 1999, Duffy 2002).”

“Recent experiments (Jonsson and Malmqvist 2000; Downing and Leibold 2002; Duffy 2002; Paine 2002; Duffy et al. 2003, 2005) have showed that trophic interactions can indeed profoundly affect the relationship between biodiversity and ecosystem functioning.”

“For example, a better knowledge of the interactions between predators and prey may improve our understanding of how consumers affect important measures of ecosystem function, such as productivity (Duffy 2002; Paine 2002).”

“However, in many systems, multiple consumers play similar roles, making it difficult to predict how the loss of any individual species will impact the overall structure and function of the ecosystem (Duffy 2002).”

“The functional-group diversity of a system refers to howmany functions are performed within the system by the organisms that compose it (Duffy, 2002).”

“There is mounting evidence that large fauna has a strong influence on the structure, functioning, and resilience of marine ecosystems for several reasons (Duffy 2002; Myers et al.”

“A complete understanding of the relationship between diversity and biomass, and therefore of the consequences of biodiversity loss, will require an understanding of how species interact within food webs (Duffy 2002).”

“However, the situation in most ecosystems might be even more complex, as beside hosts and pathogens further components are involved in food-webs (Duffy 2002).”

“First, consumers in higher trophic levels of ecosystems can have important effects on diversity– productivity relationships (Gutierrez et al. 1997; Duffy 2002, 2003; Paine 2002; Worm et al. 2002; Dyer & Letourneau 2003; Schmitz 2003; Thébault & Loreau 2003).”

“The ecological processes, functionality and restoration efforts within this distinct ecosystem are probably being substantially impaired by the disappearance of once common mammalian predators and herbivores [4–6].”

“It is known that marine communities may be regulated by ‘top-down’ and/or ‘bottom-up’ processes (Menge 2000, Duffy & Hay 2001, Duffy 2002).”

“The effect of biodiversity on prey attack rates seems to depend on the trophic level at which diversity is considered (Duffy 2002).”

“From biodiversity–ecosystem function research, we know that plant biomass production increases with plant species richness and that sampling effects and niche complementarity are the two mechanisms driving this relationship (Cardinale et al., 2009; Duffy, 2002).”

“Furthermore, as noted, warming should have changed species diversity and hence the strength of the top-down control of rodents on AGB, a suggested by Duffy (2002) and Hillebrand, Bennett &Cadotte (2008).”

“In this con- text, the relationship between herbivore diversity and func- tion in response to physical gradients has been the focus of extensive interest (McNaughton 1994; Steneck & Dethier 1994; Hooper & Vitousek 1997; Duffy 2002; Burkepile & Hay 2008; Halpern & Floeter 2008; Poore et al. 2012).”

“Litter decomposition is an important ecosystem process that releases carbon to the atmosphere and nutrients in forms that can be used for plant and microbial production (Chapin et al., 2002; Duffy, 2002).”

“The diversity of biological communities plays a key-role in determining the functioning of ecosystems (Laureau et al. 2001; Kinzing et al. 2002), and this is realised through trophic interactions and their indirect effects on other ecosystem processes (Duffy 2002; Naeem 2002).”

“…been incorporated into experimental systems to test empirical relationships (e.g. flow, Biles et al. 2003; regional attributes, Emmerson et al. 2001; grazers, Duffy 2002, Hagerthey et al. 2002) using an approach (Raffaelli et al. 2003) that is analogous to This journal is q 2007 The Royal Society”

“This pattern implies that consumers sometimes influence ecosystem processes disproportionately to their abundance (Duffy 2002), although the impact of a species in an ecosystem is a function of both per capita effects and abundance (Rosenfeld 2002).”

“Although the linkages between biodiversity and ecosystem function are an area of intense research and debate (Duffy, 2002; Schmid et al., 2009; Tilman, 1999), there are significant gaps in our understanding of how species loss and declines affect ecosystem function, particularly in freshwater systems (Covich et al.”

“…may be more resistant and/or resilient to invasion by other species for a variety of reasons, including diversity of algal size, presence of silica frustules (diatoms), specificity of predator-prey dynamics [23,131,132], and production of compounds that inhibit predators and pathogens [133].”

“Variability in predation risk is a common caveat of trophic cascade theory, where compensatory increases in less vulnerable species within high predation environments can alleviate effects of predators on resource dynamics (Hunter and Price 1992, Persson 1999, Duffy 2002 ).”

“…the last 15 years, TMIIs have been increasingly recognized as comparable in importance to DMIIs in green-world cascades and are now viewed as integral to understanding the indirect effects of predators on plants (see Duffy 2002; Werner & Peacor 2003; Schmitz, Krivan & Ovadia 2004; Schmitz 2008).”

“37 This technique of pest control was recently investigated by Shurin et al. in a set of laboratory experiments, the results of which are summarized in Fig.”

“If the dominance of trophic interactions by few species can result in less stability (sensu Duffy 2002), the higher evenness of trophic interactions observed in the southernmost site could translate into a higher functional redundancy of trophic links and would provide more stability and resistance…”

“Further, although many studies have focused on producer communities, only a few have examined the loss of consumers (Duffy 2002), and most of these have focused on a single consumer group (Jonsson and Malmqvist 2000; Cardinale et al. 2002).”

“Complementarity in resource acquisition may thus be a fundamental property of diverse herbivore communities (Duffy 2002; see also recent evidence for large African herbivores, Kartzinel et al. 2015), ultimately determining their impact on plant communities.”

“Effects of consumer diversity on ecosystem structure and function, however, may be different from those of plant diversity (Duffy 2002, Holt and Loreau 2002, Naeem 2002).”

“Duffy (2002) showed that palatability is an important mechanism linking diversity and ecosystem functioning, as diverse prey assemblages have a greater chance of containing less edible species.”

“, 2014; Olff & Ritchie, 1998; Schmitz, 2006) and community biomass (e.g. Bakker et al., 2006; Duffy, 2002; Eisenhauer et al., 2011; McNaughton, 1985), the most commonly studied effects of herbivores on plant community variation, did not appear to consistently affect plant diversity in the global experiment when consid…”

“Key words: attack rates; food webs; functional response; Haustrum scobina; New Zealand intertidal; parameter estimation; per capita interaction strengths; species interactions; whelks; Xenostrobus pulex.”

“The bias toward studies of plant communities may also substantially limit our ability to derive general conclusions from BEF research, because plants and heterotrophs exhibit fundamental differences in resource acquisition (Duffy 2002).”

“Regarding the consumption of plants by herbivores, the ‘variance in edibility hypothesis’ [15,16] posits that a resource base with more species is more likely to contain at least one species that is resistant to consumption, which can then dominate in the presence of consumers and lead to less herbivory.”

“An important but poorly studied question is how the species composition of guilds of top predators, and by extension their effects on community structure, vary geographically (Duffy 2002).”

“Ecology Letters (2010) 13: 553–563 I N T R O D U C T I O N The top-down effects of consumers are integral to the structure and functioning of ecosystems (Duffy 2002).”

“In contrast, predators, particularly large-bodied vertebrates, are more susceptible to anthropogenic extinction than most plants and small animals (Duffy 2002, 2003, Byrnes et al. 2007).”

“Human-induced extinctions and lo-cal extirpations are often biased towards higher trophic levels (Pauly et al. 1998; Jackson et al. 2001; Duffy 2002; Byrnes et al. 2005), and that losses of even one or two species that belong to higher trophic levels can cause cascading effects on species present…”

“A growing number of experimental studies examine the relationship between predator biodiversity and the strength of herbivore suppression, and this topic has been extensively reviewed (Duffy, 2002; Snyder et al., 2005; Ives et al., 2005; Tscharntke et al., 2005; Cardinale et al. 2006a,b; Casula et al., 2006; Straub an…”

“The way in which foraging animals distribute themselves can have important impacts on community structure and ecosystem function (Huntly 1991; Duffy 2002).”

“The effects of plant diversity may be common and similar to those of terrestrial systems (DUARTE, 2000; BRUNO et al., 2005), and generally weaker than the effects of consumers (DUFFY, 2002).”

“It is necessary to study food web structure and complexity to detect the consequences of diversity changes thought the trophic cascade (Duffy, 2002).”

“Effects of biodiversity are just as likely, or more likely, to be driven by the consumer level as the level of plants (Petchey et al. 1999, Duffy 2002, 2003), and these effects will lead to further effects via trophic interactions (Naeem et al. 2000, Worm & Duffy 2003, Duffy et al. 2005).”

“First, depauperate ecological systems with low herbivore diversity are most likely to exhibit a trophic cascade when exposed to an apex predator, because fewer grazing species are available to compensate for the predation of preferred herbivore prey (Duffy 2002).”

“We show that the well-known positive (and negative) effects of horizontal (and vertical) diversity on consumer biomass (Duffy 2002; Cardinale et al. 2003) underpin these proposed effects.”

“The existence of multiple trophic levels in natural trophic webs generates complex BEF relationships [9,128].”

“…at the horizontal (within trophic level, e.g. competing filter feeders) or vertical (consumers, e.g. predatory mud crabs) levels of diversity (Duffy 2002); (2) Does the presence of adult invasive crabs facilitate recruitment; and (3) What role does propagule pressure play in invasion success?”

“Less clearly understood are the impacts of loss at higher trophic levels, such as large herbivores, on composition and structure of lower trophic-level communities (Duffy 2002).”

“In such a diverse community, interactions within and between trophic levels become important for the regulation of the producer assemblage (4, 5).”

“The complete evolutionary absence or disproportionate loss of functional groups, such as top predators ( Duffy 2002 ), may predispose habitats to decreased biotic resistance or increased ecological impact of introduced species.”

“Recently, the debate on the relationship between diversity and ecosystem stability has intensified, fuelled by concern about the consequences of worldwide biodiversity loss on ecosystems [3,14-21].”

“Research also shows increased associational resistance against consumers in prey alga assemblages (50) due to various possible mechanisms (51).”

“However, they tend to be the first to go due to their lower biomass and larger body size (Duffy, 2002), which is appreciated for human consumption (Jackson et al.”

“Overharvesting top marine consumers has led to the collapse of shallow-water marine ecosystems around the globe (Jackson et al. 2001; Duffy 2002), including coral reefs (Hughes et al. 2003), sea grass beds (Jackson 1997), and kelp forests (Estes et al. 1998).”

“89 2005) and the bias toward extirpation among higher-order consumers (Duffy 2002).”

“…seagrasses (e.g. kelps, corals, salt marsh grasses), the strong role of consumer control of producer biomass (Paine 2002), as well as changes in consumer abundance and diversity in these systems (Jackson et al. 2001, Duffy 2002, Byrnes et al. 2007), the phenomena we describe here may be widespread.”

“, 2001) and studies of ecosystem function using multitrophic communities have only rarely been reported (Duffy, 2002; Finke & Denno, 2002; Paine, 1966, 2002; Snyder & Wise, 2001).”

“…high population densities of green turtles in the Lakshadweep islands provide a unique opportunity to examine top-down control on the functioning of seagrass meadows (Duffy 2002) under the influence of high megaherbivore densities, comparable to putative historical estimates (Jackson 1997, 2001).”

“1995; Duffy 2002).”

“…(e.g., Schulze and Mooney 1993), more recent studies have started to address the effects of species diversity on trophic interactions (e.g., Duffy 2002, Cardinale et al. 2003, Schmitz 2003), for example, between plants and herbivorous insects (Weisser and Siemann 2004, van Ruijven et al.…”

“The transfer of energy (or carbon) through an ecosystem represents one such ecosystem process and interaction strengths provide a direct link between the diversity and ecosystem functioning of a community and its ecological stability (Duffy, 2002).”

“Diet complementarity among predators may increase overall effects on lower trophic levels (Duffy 2002; Hooper et al . 2005); however, effects of some complementary predators may be substitutable (Schmitz & Sokol-Hessner 2002).”