Patterns of impact of three invasive plant species on freshwater ecosystems Iris Stiers & Ludwig Triest Vrije Universiteit Brussel, Plant Biology and Nature Management, BELGIUM
freshwater ecosystem WITHOUT alien aquatic plants complex interactions between biological communities structure macrophyte assemblage determines composition of: macroinvertebrates and fish phyto and zooplankton pollinators and water birds
freshwater ecosystem WITH alien aquatic plants new interactions between almost every biological community identity and density of the alien will play a role Strong interdependence difficult to predict impacts
Overview of the ecological impacts of invasive aquatic plants on different biological communities Plants Invertebrates Fish
Overview of the ecological impacts of invasive aquatic plants on different biological communities +++ extensively documented; ++ fairly documented; + rarely documented;? not documented; / not applicable Invasive aquatic species growth form native plants fish macroinvertebrate s phytoplankton zooplankton pollinators water birds submerged +++ +++ +++? + / + free floating / floating leaved ++ + + + +? + emergent +++ + +? + ++ + amphibious +?????? studies that quantify community level impacts are still scarce minimal amount of studies that incorporate density effect The good, the bad, (the ugly ) ~ The white, the black, the grey
in will come the migrants, from lands of warmer hue, exotics, plant and animal, to make everywhere a zoo Name: Myriophyllum aquaticum Family: Haloragaceae Growth form: amphibious Origin: S America 1st observation Belgium: 1983 Name: Ludwigia grandiflora Family: Onagraceae Growth form: amphibious Origin: S America 1st observation Belgium: 1983 Name: Hydrocotyle ranunculoides Family: Apiaceae Growth form: amphibious Origin: N and S America 1st observation Belgium: 1992 Introduced through the aquarium trade Tolerance to wide range of nutrient levels Vegetative reproduction Rapid and extensive growth Ecological and economical impacts
AIM: 3 amphibious species community level impacts I. Impact on native plants What is the direction and magnitude of impact on native plant richness, cover, and composition? II. Impact on benthic macroinvertebrates (decomposed alien litter) What is the direction and magnitude of impact on taxa richness, invertebrate abundance and composition? III. Impact on pollinators (only L. grandiflora) What is the direction and magnitude of impact on pollinator abundance and composition? What is the impact on visitation rate and seed number of a native plant? density effect (% cover alien)
Belgium Hydrocotyle ranunculoides Ludwigia grandiflora Myriophyllum aquaticum Study sites 32 ponds 3 ponds, 2 consecutive years Located in nature reserves Small (< 1ha) Shallow (max. depth 3 4m)
Uninvaded ponds Invaded ponds I. Impact on native plants Not (yet) invaded plots (A) Semi invaded plots (B) Heavily invaded plots (C) POND Native plant cover PLOT Species richness Species composition
Uninvaded ponds II. Impact on benthic macroinvertebrates Invaded ponds POND Invertebrate abundance POND Taxa richness Taxa composition
No cover ponds III. Impact on pollinators Low cover ponds High cover ponds Native Lythrum salicaria POND Pollinator abundance Pollinator composition Visitation rate Seed number native
I. Impact on native plants plant species richness native plant cover 67% 70% 57% P O N D a Native species cover (% range) 1-5 5-25 25-50 50-75 75-100 5 4 3 2 1 Γ = -0.60, P < 0.01 P L O T 0 0 1-5 1 5-25 2 25-50 3 50-75 4 75-100 5 Invasive species cover (% range) Decrease in native plant cover with increasing alien cover Not (yet) invaded A plots harboured more species than heavily invaded C plots Stronger impact of L. grandiflora Stiers et al. (2011) Biol Invasions 13: 2715 2726
I. Impact on native plants plant composition P L O T Difference in species composition for H. ranunculoides and L. grandiflora Stiers et al. (2011) Biol Invasions 13: 2715 2726
I. Impact on native plants plant composition P L O T 4 out 14 tested species exhibited significant differences in abundance amongst the different invasion categories Submerged, floating and emergent species affected No species was more abundant in C plots Difference in native species composition due to changes in species presences rather than abundances Stiers et al. (2011) Biol Invasions 13: 2715 2726
II. Impact on benthic macroinvertebrates taxa richness and composition invertebrate abundance 17 10 9 14 Decrease of invertebrate abundance with increasing alien cover High similarity (range 52 80%) in dominant taxonomic groups higher taxon richness in uninvaded ponds Stiers et al. (2011) Biol Invasions 13: 2715 2726
II. Impact on benthic macroinvertebrates invertebrate composition Unchanged Aquatic worms Biting midges Non biting midges Proportions lower/ absent under alien vegetation absent Phantom midges Isopods Mayflies Amphipods Snails Clams Leeches Stiers et al. (2011) Biol Invasions 13: 2715 2726
III. Impact on pollinators pollinator abundance and composition With L. grandiflora present in low and high abundance, L. salicaria experiences respectively 1.7 and 2.6 times more pollinators Stiers et al. submitted
III. Impact on pollinators pollinator abundance and composition With L. grandiflora present in low and high abundance, L. salicaria experiences respectively 1.7 and 2.6 times more pollinators Change in composition for L. salicaria: No cover: absence Apis mellifera Low cover: presence Apis mellifera High cover: absence Apis mellifera Apis mellifera Stiers et al. submitted
III. Impact on pollinators Visitation rate 1.6 1.4 1.2 1 0.8 0.6 visitation rate c d L. grandiflora L. salicaria Low cover: due to A. mellifera more visits to native L. salicaria compared to control Weak facilitation effect 0.4 0.2 0 a b a no cover low cover high cover Stiers et al. submitted
III. Impact on pollinators visitation rate 1.6 1.4 1.2 d L. grandiflora L. salicaria Low cover: due to A. mellifera more visits to native L. salicaria compared to control Weak facilitation effect Visitation rate 1 0.8 0.6 0.4 0.2 0 c a b a no cover low cover high cover Dissapears at high cover A. mellifera prefers L. grandiflora Invasive more efficiently visited without turning other pollinators away from the native seed number L. salicaria no effect Stiers et al. submitted
With increasing alien cover: species native plants pollinators macroinvertebrates H. ranunculoides plant richness plant cover change compostion / abundance taxa richness change composition plant richness L. grandiflora plant cover seed number change composition M. aquaticum plant richness plant cover no change composition abundance visitation rate change composition abundance taxa richness change composition / abundance taxa richness change composition Impacts can be +,, or but are related to cover of the alien plant Magnitude is invasive species specific Competition for pollinator services are minor
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