# How environmental variables shape wetland food webs

Camille Leclerc, Julie Crabot, Benjamin Bergerot, Olivier Gore, Anne Bonis,
J.M. Paillisson

► To cite this version:

Camille Leclerc, Julie Crabot, Benjamin Bergerot, Olivier Gore, Anne Bonis, et al.. How environmen-
tal variables shape wetland food webs. International Congress in Ecology & Evolution - SFE², Oct
2024, Lyon, France. hal-04954480

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# How Environmental Variables Shape Wetland Food Webs: Insights from Marais Poitevin Ditches

Camille Leclerc, Julie Crabot, Benjamin Bergerot, Olivier Gore, Anne Bonis, Jean-Marc Paillisson

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# Hydrology's role in wetlands

**Hydrology** – the amplitude of water levels, as well as the duration and timing of water presence

* plays an important role in **shaping wetland ecosystems** and their **biodiversity**

* is **influenced by both natural processes** and **human activities**

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© PNR Marais poitevin

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© Bernard Janneau

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© Pascal Trinh Van

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© PNR Marais poitevin
# Hydrology's role in wetlands

Research has focused on how specific aquatic organisms respond to fluctuating hydrological conditions in wetlands regarding their occurrence, abundance, biomass, and life history traits

The challenge of the duration and timing of water levels, a small part of the equation

Thecha driven factors, ecosystem

## Patterns of larval amphibian distribution along a wetland hydroperiod gradient

Kimberly J. Babbitt, Matthew J. Baber, and Tracy L. Tarr

**Abstract:** We investigated the response of pond-dominating amphibian assemblages to wet and predator changes (interventions) (abundance and richness) and fish (prosencephala) landscapes in southern New Hampshire, U.S.A. We sampled 42 wetlands for larval am (each with a sheet, intermediate, and permanent-hydroperiod wetlands) in 1998 and 1999. 16-hydroperiod wetlands (48 months) were separated (4 species only compared with permanent but ~4 months) and permanent wetlands, which included 7 species, no absence did not vary among hydroperiod categories. Species distributions along the line of the wet. *Rana catesbiana* dominated wetlands with short and intermediate hydroperiods, w americans, *Rana clavipes*, and *Pseudacris cricetus* dominated in those with a longer wetland, and wetlands with species richness and abundance did not differ with respect to the though there were species-compositional differences. Amphibian species richness and at the same time the abundance and richness of predator interventors, suggesting that both predator assemblages may be responding similarly in differences in wetland characteris cants. Our results are consistent with our expectations, and should be incorporated into equations and legislation designed to protect hydro

**Résumé:** Nous avons examiné la réaction d'un peuplement d'amphibians, qui se repère l'hydrophoride de terres humides et aux changements associés dans la flotte des prairies de l'Estrie (44 mois) en comparaison des terres humides à hydrophoride, en comparaison des terres humides à hydrophoride, en comparaison des terres humides à hydrophoride que *Rana catesbiana*, *Bufo americans*, *Rana clavipes* et *Pseudacris cricetus* le font hydrophoride plus long. Dans les terres humides permanentes, la richesse spécifique et l'abondance sont plus élevées que dans les terres humides temporaires (comparaison avec terres humides à hydrophoride). La richesse spécifique et l'abondance des amphibians sont en correlation positive et la richesse spécifique et l'abondance des terres humides sont en correlation négative. Des analyses de covariance ont montré que des variations de l'abondance des terres humides et des variations de la richesse et la abondance de terres humides, expérimentes de ce kind, can assist in predicting vege

[Traduit par la Révision]

### Introduction

In freshwater lens habitats, the hydrological gradient ranges from ephemeral pools to permanent ponds and lakes, and has long duration. It is important to understand the abundance and distribution of organisms. Numerous amphib-

ian species use these habitats. Larval growth and development of these species depend on a wide range of amphibian assemblages (Checa et al. 1996; Skelly 1997). This is due to the influence of the hydroperiod, which affects the specific differences in the tim

Received 2 January 2003. Accepted 15 July 2003. Published on the NRC Research Press Web site, 29 September 2003.

K.J. Babbitt, M.J. Baber, and T.L. Tarr. Department of Natural Resources, University of New York, 1100, 01324, U.S.A.

(Corresponding author: e-mail: kbbitt@comcast.net, U.S.A.)

Present address: NH Soil Consultants, Inc., Newmarket, NH 03857, U.S.A.

Cm. J. Zondi #1 1539-1552 (2003) 60.119.203-131

1530

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© Freshwater Biology 145: 237-260, 2003
© 2003 Blackwell Publishing Ltd, London, UK

### How do depth, duration and frequency of flooding influence the establishment of plant communities?

Michelle T. Casanova* & Margaret A. Brock

Bartolomé, School of Biology and Earth Sciences, University of New England, Armidale, N 2351, Australia. (*Current address: RMB 1620 Wemmer, Victoria 3351, Australia)

(Received 6 November 1998; accepted 6 November 1999)

Key words: Disturbance, Fluctuations, Seed bank, Water-level, Water regime, Zonation

### Abstract

In many temporary wetlands such as those on the Northern Tablelands of New South Wales Australia, plant community is largely the result of growth and establishment from a long-lived bank, and vegetation patterns that survive drought. In these wetlands the plant community, over a time span of 10 years to 20 years, is not always a good indicator of the plant community. Different wetlands have different hydroperiods, and the pattern of development of important in the development of plant communities an experiment using seed bank as undertaken over a 16 week period in late spring-early summer 1995-1996. Seed bank samples w 17 different water-level treatments with different depths, durations and frequencies of flooding. S and homas of the communities that established from the seed bank were assessed at the end of the data were examined to determine which aspects of water regime were important in the different communities. It was found that depth, duration and frequency of inundation influenced pH composition, but depth was least important, and also that the duration of individual flooding events in the wetland was important. Species composition, their ability to fluctuate in flooding and drying. The highest homas and species richness developed in pot t floods. Less than half of species richness in the understorey. Water regimes an promote regeneration and cover of structurally dominant taxa and increase richness in the understorey. The study demonstrates a strong association vegetation and the diverse water regimes that exist within a single wetland will be useful for modelling the effects of modified water regimes on wet

### Introduction

Water regime is a major determinant of plant community development and patterns of plant rotation in wetlands. It can be described by the depth, duration, frequency, rate of filling and drying, timing and predictability of flooded and dry phases in a wetland (Thorne et al. 1997). Wetlands on the Northern Tablelands of New South Wales, Australia have a range of different catchments, soil, rainfall and tem-

perature characteristics and so expert advice on plant community development and management is essential. This review provides a broad overview of the literature which dominantly in the winter from northern low-pressure systems in the summer and autumns, so the water regimes of flooded or droughts in any wetlands, and the larger inter-annual water regime produce a variety of p

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Freshwater Biology (2003) 88, 701-715

doi:10.1111/j.1365-2427.2003.02311.x

## The importance of water regimes operating at small spatial scales for the diversity and structure of wetland vegetation

ELISIA J. RAULINGS*, KAY MORRIS*, MICHAEL C. ROACHE* AND PAUL I. BOON

*Australian Centre for Biodiversity, School of Biological Sciences, Monash University, Clayton, Vic., Australia

*Institute for Sustainability and Innovation, Victoria University, St Alans, Vic., Australia

### SUMMARY

1. In most cases, the most important determinant of wetland vegetation is that although water regime is usually described and managed at the scale of the wet the patterning of vegetation is likely to be determined by water regimes that at much finer spatial scales. In this study, we investigated the effects of different hydroperiods along the hydroperiod gradient. In this study, we investigated the effects of different hydroperiod lengths on the functional structure of Odonata assemblages in non-persistent wetlands (positively classified as "short", "medium" and "long-hydroperiod" in southern Brazil) in 2013 and 2014. Biological traits related to life-history strategies in temporary waters were assessed according to seasonal patterns of occurrence of nymphal and adult stages of odonates. Following the rationale of an environmental filter produced by hydroperiod, we ex- pected to find (1) higher functional diversity in longer hydroperiods (2) trait-convergence patterns in odonate assemblages in shorter hydroperiods. Patterns of functional diversity were detected along the hydroperiod grad- en. More specifically, higher functional diversity was found in long-hydroperiod wetlands and trait-convergence patterns occurred in wetlands with short hydroperiods. Odonate taxa with life-history traits associated with shorter life cycles predominated in medium- and short-hydroperiod wetlands. Our results thus suggest that more pronounced reductions in wetland hydroperiod length should produce odonate assemblages functionally more similar, and these results gain special importance as climate change scenarios indicate that the hydrology of wetlands will be affected by variation in rainfall regimes.

2. The classification of water depth data indicated four distinct water regime wetland that were differentiated primarily by the duration of the dry period, of all PFGs co-existed over small spatial scales where topographical variants and the richness and cover of understorey species declined as tracts became and permanently flooded. Some PFGs (e.g. amphibians fluctuation tolerators) and amphibians fluctuation responder-morphologically plastic) were eliminated extended periods of flooding, which increased the cover but not richness of plants. Species richness and foliage projective cover declined as water regime shallow and frequently exposed conditions to regimes typified by deeper and more inundated. Cover of the structurally dominant woody species was compromised flooded conditions but vegetative regeneration occurred despite high water levels. 4. Internal topographical variation generates monospecific water regimes at f that allow plant species with different water regime requirements to co- distances. Deep water and an absence of dry periods result in decreased f and an overall loss of species richness in the understorey. Water regimes an promote regeneration and cover of structurally dominant taxa and increase richness in the understorey. The study demonstrates a strong association vegetation and the diverse water regimes that exist within a single wetland will be useful for modelling the effects of modified water regimes on wet

Keywords: plant functional groups, water regimes, wetland duration, wetlands

## Austral Entomology

Austral Entomology (2017) 11, 1-10

Matéus M Pires,¹* e Cristina Stener¹ and Leonardo Maltich¹

¹*Laboratory of Ecology and Evolution, Vida do Tanguay University, La Gallegos, RS, Brazil

²*Laboratory of Ecology and Conservation of Aquatic Ecosystems, UNSIDIN, São Leopoldo, RS, Brazil.

### Abstract

The role of hydroperiod as an environmental filter in structuring wetland assemblages is usually associated with trait selection in invertebrates. However, the effects of changes in the hydroperiod of non-persistent wetlands on intermediate assemblages are still unclear, and few studies have assessed the functional structure of insect as- semblages along the hydroperiod gradient. In this study, we investigated the effects of different hydroperiod lengths on the functional structure of Odonata assemblages in non-persistent wetlands (positively classified as "short", "medium" and "long-hydroperiod" in southern Brazil) in 2013 and 2014. Biological traits related to life-history strategies in temporary waters were assessed according to seasonal patterns of occurrence of nymphal and adult stages of odonates. Following the rationale of an environmental filter produced by hydroperiod, we ex- pected to find (1) higher functional diversity in longer hydroperiods (2) trait-convergence patterns in odonate assemblages in shorter hydroperiods. Patterns of functional diversity were detected along the hydroperiod grad- en. More specifically, higher functional diversity was found in long-hydroperiod wetlands and trait-convergence patterns occurred in wetlands with short hydroperiods. Odonate taxa with life-history traits associated with shorter life cycles predominated in medium- and short-hydroperiod wetlands. Our results thus suggest that more pronounced reductions in wetland hydroperiod length should produce odonate assemblages functionally more similar, and these results gain special importance as climate change scenarios indicate that the hydrology of wetlands will be affected by variation in rainfall regimes.

### Key words

### INTRODUCTION

Functional ecology relies on tab-based approaches to assess species' responses to environmental changes (Vilela et al. 2007; Verbeek et al. 2013). Traits may be considered "functional" if they impact organisms' times and if they are affected by the environment ("response traits", see Vilela et al. 2007). Therefore, the functional structure of communi- ties can be influenced by environmental changes, and consequently, trait-based approaches have been increasingly used to predict community-level responses to them (Verbeek et al. 2013). For instance, patterns like trait-convergence arise when species with similar traits predominate in specific habitat conditions produced by environmental filtering (Keddy 1992; Wilson 1999). On the other hand, species can be prevented from being functionally too similar by limiting similarity mechanisms, like biotic interactions, generating trai- d divergence patterns (Wilson & Sibbitts 2004; Wilson 2007).

Environmental differences can act in either on macroecosystem assemblages in freshwater ecosystems (Poff et al. 1997, 2006). However, functional approaches have largely focused on late systems (Doblete & Sznat 2010; Heins et al. 2013; Schenker et al. 2017). In wetlands, hydroperiod is considered the major driving force in macroecosystem trait selection

(Wellborn et al. 1996) and an environmental filter for investi- gated species (Rahi et al. 2014). Species with life-history traits associated with survival for dry periods are favored in non-persistent sites (Bater & Wrennig 1996; Wellborn et al. 1996, 2006), including shorter life cycles, develop- ment of diapause and active diapause (Rahi et al. 2013; Bater & Bater 2016). Also, the tendency of some macroecosystem to avoid specializing for specific hydroperiod types can be considered a strategy to overcome dry periods (generalist habit) (Bater et al. 2004; Bater & Shunt 2014).

General reviews have shown that macroecosystem assemblages are more functionally similar in non-persistent wetlands than in permanent ones, i.e. they have lower trait richness and show higher functional overlap (Rahi et al. 2012, 2013). Though, surprisingly, field studies on the functional structure of wetland macroecosystems are scarce in the literature. Additionally, the effects of different hydroperiod lengths of non-persistent wetlands on macroecosystem re- main much less studied (see review in Bater 2017). This lack of knowledge has special importance as climate change scenario indicate that variation in rainfall regimes should alter the hydrology of freshwater ecosystems like wetlands and thus affect their biodiversity (Jank 2013; Twiley & Britson 2014). Odonates occur along the whole hydroperiod gradient during their nymphal stage (Cobert 2003). Variation in 'response' life-history traits related to changes in hydroperiod length has been described in odonates. Shorter hydroperiods

*nemouris@paul.gmu.edu

© 2017 Australian Entomological Society

doi:10.1111/aen.12312
# Food webs: Key to analyzing environmental gradients in wetlands

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Barnes et al. 2018 [doi: 10.1016/j.tree.2017.12.007]

A **food-web approach** examines the network of feeding interactions between co-occurring species within a community

↔ promotes a **more comprehensive and integrated understanding** of the effects of **environmental changes on biodiversity and ecosystem functioning**
Investigate how food webs in drainage ditches of the Marais Poitevin, a large eutrophic agricultural marshland, respond to key environmental drivers

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EPMP®

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PNR Marais Poitevin ©
# Methods: Data set

## Study site & aquatic macrofauna

<figure><img src="image_13.png" /><figcaption>11 hydrological blocks × 5 ditch stations (intra-blocks) aquatic macrofauna (n = 55)
Monitoring over 8 years: 2014 – 2021</figcaption></figure>

Sources: IGG/D'Topo®, EPMP / Conception et réalisation: EPMP et ECOBIO, octobre 2017

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# Methods: Data set

## Study site & aquatic macrofauna

Localisation des unités hydrauliques retenues
Suivi biodiversité en lien avec la gestion de l'eau

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11 hydrological blocks × 5 ditch stations (intra-blocks) aquatic macrofauna (n = 55)
Monitoring over 8 years: 2014 – 2021

Sources: IGCN / BDTopo®, EPMP / Conception et réalisation: EPMP et ECOBIO, octobre 2021

<figure><img src="image_18.png" /></figure>

**Fish**
15 taxa
(from species to genus)

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**Amphibians**
3 taxa
(from species to genus)

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**Macroinvertebrates**
41 taxa
(from species to phylum)

+ 7 general taxonomic groups

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Zooplankton

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Phytoplankton

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Periphyton

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Macrophytes

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Protists

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Bacteria

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Detritus and
organic matter

Icons from Phytopic
# Methods: Food-web reconstruction and topology

## Metaweb

contains all the potential interactions between the 66 taxa identified in the 55 ditches of our dataset

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Trophic links were retrieved from the AquaticWeb database (developed by Gérard Lacroix), which compiles empirically proven links in aquatic ecosystems from peer-reviewed studies
# Methods: Food-web reconstruction and topology

## Metaweb

contains all the potential interactions between the 66 taxa identified in the 55 ditches of our dataset

<figure><img src="image_29.png" /></figure>

Trophic links were retrieved from the AquaticWeb database (developed by Gérard Lacroix), which compiles empirically proven links in aquatic ecosystems from peer-reviewed studies

## Local taxa pools

set of taxa in each sampled ditch

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Icons from Phytopic
# Methods: Food-web reconstruction and topology

## Metaweb

contains all the potential interactions between the 66 taxa identified in the 55 ditches of our dataset

<figure><img src="image_31.png" /></figure>

○ = 1 taxon

Trophic links were retrieved from the AquaticWeb database (developed by Gérard Lacroix), which compiles empirically proven links in aquatic ecosystems from peer-reviewed studies

## Local taxa pools

set of taxa in each sampled ditch

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<figure><img src="image_33.png" /></figure>

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Icons from Phylopic

...

## Local food webs

network of feeding relationships among taxa within each sampled ditch

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# Methods: Food-web reconstruction and topology

## Local food webs

network of feeding relationships among taxa within each sampled ditch

<figure><img src="image_38.png" /></figure>

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Four metrics were computed to characterize each ditch food web structure,

### Connectance

proportion of all possible links that are realized in the food web

### Maximum trophic level

highest trophic level occupied by a consumer in the food web

### Proportion of top predators

proportion of taxa that are not consumed by other taxa in the food web

### Proportion of omnivores

proportion of taxa that feed on more than one trophic level
# Methods: Investigating food-web responses to environmental variables using a SEM approach

## Structural Equation Model (SEM) Approach

* integrates multiple **predictor** and **response variables** into a causal network, where paths represent hypothesized relationships

* useful for analyzing **direct, indirect** (mediated by other variables), **and total effects** (sum of direct and indirect) of predictors on a response variable

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# Results: Structural variations among 55 ditches

## Proportion of top predators

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## Proportion of omnivores

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## Connectance

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## Maximum trophic level

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## Food webs in ditches:

* Predominantly composed of omnivores, with few top predators

* Low proportion of realized trophic links

* Vertically structured, supporting taxa at high trophic levels
# Results: The total effect of environmental variables on food web topology

From the SEM analysis

Response variable:

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Connectance

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Hydrology

adj. grasslands
flooding duration

water lev. fluct. /
drought duration

<figure><img src="image_48.png" /></figure>

Habitat size /
connectivity

ditch width /
mean water lev.

linear dens.
connect. ditches

<figure><img src="image_49.png" /></figure>

Aquatic
vegetation

vegetal cover /
species richness
of hydrophytes

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* Positive total effect of drought duration and water level fluctuations

* Negative total effect of habitat size and aquatic vegetation
# Results: The total effect of environmental variables on food web topology

From the SEM analysis

<figure><img src="image_51.png" /></figure>

Hydrology

adj. grasslands
flooding duration

water lev. fluct. /
drought duration

<figure><img src="image_52.png" /></figure>

Habitat size /
connectivity

ditch width /
mean water lev.

linear dens.
connect. ditches

<figure><img src="image_53.png" /></figure>

Aquatic
vegetation

vegetal cover /
species richness
of hydrophytes

Response variable:

<figure><img src="image_54.png" /></figure>

Connectance

<figure><img src="image_55.png" /></figure>

Response variable:

<figure><img src="image_56.png" /></figure>

Maximum
trophic level

<figure><img src="image_57.png" /></figure>

* Positive total effect of habitat size and aquatic vegetation

* Flooding's negative direct effect was offset by an indirect positive effect, especially by favoring more complex aquatic vegetation. As a result, its total effect was not significant
Take-home messages

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Large baseline aquatic habitats, complex vegetation, and stable hydrological conditions enhance food webs with long chains and low connectance

↔ These findings can guide management strategies, especially in highly human-modified systems
Thank you!

Any questions?

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camille.leclerc@uca.fr