Positive indirect effect of tadpoles on a detritivore through nutrient regeneration

Iwai, Noriko; Kagaya, Takashi

doi:10.1007/s00442-007-0682-6

Cited by 23 publications

(19 citation statements)

References 47 publications

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“…This suggests that the main resource for tadpoles in Birthday Creek should be leaf litter as we simulated in our experiments. However, nutrient concentrations are generally low in leaf litter (Bowen, 1987), and its consumption may not release sufficient nutrients to alter other system processes that influence leaf litter decomposition (Iwai & Kagaya, 2007). This may be why we did not detect any nutrient regeneration effect by consumers.…”

Section: Discussionmentioning

confidence: 99%

“…Because the biomass and activity of detritus‐associated microbes are often limited by nitrogen or phosphorus in the surrounding water (Suberkropp, 1998), increased nutrient concentrations can enhance microbial activity and subsequent production by invertebrates (Pearson & Connolly, 2000; Robinson & Gessner, 2000). Thus, nutrient‐releasing consumers can facilitate leaf litter consumers (Iwai & Kagaya, 2007), leading to higher leaf litter decomposition rates.…”

Section: Introductionmentioning

confidence: 99%

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Shredder–tadpole facilitation of leaf litter decomposition in a tropical stream

Iwai¹,

Pearson²,

Alford³

2009

Freshwater Biology

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1. Leaf litter decomposition is one of the most important ecosystem processes in streams. Recent studies suggest that facilitation, in which litter is processed by a succession of species with differing abilities and requirements, may be important in making the nutrients bound in litter available to the stream assemblage. 2. We predicted that stream invertebrates that feed on terrestrial leaf litter (shredders) and tadpoles would facilitate leaf litter decomposition by changing the quality of leaf material directly via physical contact or indirectly via nutrient release. We experimentally examined the ability of shredders and tadpoles to break down leaves, independently and together, in artificial streams beside a natural forest stream. 3. The decomposition rate was greater when shredders and tadpoles were together than was expected from rates in single-species treatments, indicating that facilitation occurred. This facilitation operated in one direction only: the rate of leaf breakdown by tadpoles was higher when leaves had been partly processed by shredders, but there was no similar effect when leaves previously occupied by tadpoles were processed by shredders. We did not detect facilitation caused by indirect nutrient release. 4. Shredders may have benefited tadpoles by roughening leaf surfaces, making them easier for the tadpoles to consume and enhancing leaf breakdown in the presence of both taxa. This indicates that the loss of a single species can have impacts on ecosystem functioning that go beyond the loss of its direct contribution.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Shredder–tadpole facilitation of leaf litter decomposition in a tropical stream

Iwai¹,

Pearson²,

Alford³

2009

Freshwater Biology

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“…However, influences of tadpoles on leaf decomposition may be related to functional traits. Iwai & Kagaya (2007) found that tadpole excretion decreased C : N ratios of leaves, resulting in a positive indirect effect on detritivores that enhanced decomposition. In contrast, Iwai et al (2009) found that tadpoles and invertebrates facilitated leaf decomposition.…”

Section: Introductionmentioning

confidence: 98%

“…Larval amphibians are abundant and diverse consumers in many neotropical streams, where they can influence organic and inorganic sediment dynamics (Flecker, 1996;Flecker, Feifarek & Taylor, 1999;Ranvestel et al, 2004), community structure and production of aquatic macroinvertebrates (Ranvestel et al, 2004;Coló n-Gaud et al, 2009, 2010a, and algal communities and primary production (Connelly et al, 2008). While their influences on some ecosystem processes have been quantified to some degree, there is little known of the potential roles of stream-dwelling tadpoles in leaf decomposition in neotropical streams (but see Iwai & Kagaya, 2007;Iwai, Pearson & Alford, 2009;and Connelly et al, 2011). While their influences on some ecosystem processes have been quantified to some degree, there is little known of the potential roles of stream-dwelling tadpoles in leaf decomposition in neotropical streams (but see Iwai & Kagaya, 2007;Iwai, Pearson & Alford, 2009;and Connelly et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Tadpoles enhance microbial activity and leaf decomposition in a neotropical headwater stream

2012

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Summary 1. Relationships between biodiversity and ecosystem function are of increasing interest, particularly in freshwater ecosystems where species losses are occurring at unprecedented rates. Amphibian declines have been associated with a loss of ecosystem function in neotropical streams, but little is known of the potential roles of stream‐dwelling tadpoles in leaf decomposition. Leaf litter is an important energy source to streams, and the breakdown of this material to fine particulate organic matter (FPOM) is a key ecosystem function. 2. We used mesocosms in a natural stream setting to quantify the effects of grazing tadpoles, shredding macroinvertebrates and a combination of the two on leaf decomposition and associated microbial activity. We measured respiration rates of decomposing leaves, particulate organic matter (POM) and leaf biofilm biomass and C : N : P ratios, and leaf area loss in 4 treatments: Control, tadpole only (TP), tadpole and shredding macroinvertebrates (TP + INV) and shredding macroinvertebrates only (INV). We hypothesised that tadpoles would enhance leaf decomposition by changing nutrient availability and stimulating microbial activity. 3. Respiration rates ranged from 3.1 to 6.0 mg O2 dry mass−1 h−1 and were significantly higher in the TP and TP + INV treatments than in the control. The TP + INV treatment had significantly higher POM in chambers than the control and INV treatments. The TP treatment had significantly lower leaf biofilm biomass than the control and INV treatments. 4. Tadpoles influenced the elemental balance of C and N in POM and leaf biofilm. In contrast to our prediction, molar C : N ratios were higher in the TP + INV treatment than in the control. Mean molar N : P ratios in POM were higher in the TP + INV treatment than in any other treatment. Leaf biofilm followed a similar pattern, but both TP and TP + INV had significantly higher N : P ratios than the control and INV treatments. Leaf area loss was greatest when tadpoles and invertebrates were together (TP + INV = 0.6% leaf area loss per mg organism) than separate (TP = 0.1%, INV = 3%), indicating facilitation. 5. Tadpoles indirectly affected leaf decomposition by influencing microbial communities and macroinvertebrate feeding. As such, ongoing amphibian declines may adversely affect a critical ecosystem function in freshwater habitats.

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“…Experimental nutrient enrichment in streams has often enhanced activity of microbes associated with leaf detritus, leading to increased N or P content (Elwood et al 1981, Gulis et al 2004) and/or faster mass loss by leaves (Bärlocher and Corkum 2003, Chadwick and Huryn 2003). Iwai and Kagaya (2007) demonstrated that nutrient regeneration by tadpoles led to decreased leaf C:N ratios. However, neither nutrient content increase nor mass‐loss acceleration by tadpoles occurred in this study.…”

Section: Discussionmentioning

confidence: 99%

Feeding by omnivores increases food available to consumers

Iwai

Kagaya

Alford

2011

Oikos

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Consumers are usually thought of as negatively affecting producers, but they can affect them positively by releasing nutrients (nutrient regeneration). The net effects of consumers on producers should depend on the balance between the effects of consumption and nutrient regeneration. In aquatic habitats, nutrient regeneration by consumers may increase microbial activity on leaf detritus as well as algal production, which in turn may stimulate further nutrient release and benefit herbivores or detritivores by increasing food quantity or quality. Omnivores can regenerate nutrients from animals, algae and detritus, creating diverse nutrient pathways. Many tadpoles are omnivores, and their nutrient regeneration may be important in aquatic food webs. To reveal the nutrient pathways created by tadpoles and examine whether omnivorous tadpoles can have positive effects on producers and consumers, we experimentally examined the effects of nutrient regeneration by three densities of tadpoles on primary producers, leaf litter, and other consumers in tank mesocosms. Tadpole exclosures were placed inside each mesocosm, allowing us to separate direct consumption effects from indirect nutrient regeneration effects. Nutrient regeneration caused by the herbivorous and carnivorous feeding activities of tadpoles positively affected rates of production of benthic algae, phytoplankton, and herbivorous benthic chironomid larvae, and rates of mineralization of leaf litter. The increased production of benthic algae and chironomid larvae was consumed by the tadpoles themselves, leaving no net change in the standing biomass of these resources. Our experiment thus demonstrated that omnivores created complicated nutrient pathways and accelerated rates of primary production and growth rates of other consumers, leading to increased rates of food availability to the omnivores themselves. Interactions of this nature may be common in many systems and could strongly moderate the effects of consumers on their resources and each other.

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Positive indirect effect of tadpoles on a detritivore through nutrient regeneration

Cited by 23 publications

References 47 publications

Shredder–tadpole facilitation of leaf litter decomposition in a tropical stream

Shredder–tadpole facilitation of leaf litter decomposition in a tropical stream

Tadpoles enhance microbial activity and leaf decomposition in a neotropical headwater stream

Feeding by omnivores increases food available to consumers

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