A native species does not prevent the colonization success of an introduced submerged macrophyte, even at low propagule pressure (original) (raw)
Related papers
2016
Hydrilla verticillata (L.f.) Royle is one of the most critical invasive macrophytes. Several abiotic characteristics are related to its invasion success, but it is still uncertain how biological interactions affect this success. In the Upper Paraná Freshwater ecoregion, hydrilla has invaded the main channel of Parana river but has been unable to establish in floodplain lakes. Along with abiotic filters, native and nonnative species in lakes can impose resistance to hydrilla invasion. Using empirical methods, we selected three species of aquatic organisms that potentially provide resistance to hydrilla establishment in floodplain lakes. These species were chosen to represent the most probable ecological interactions that can negatively impact hydrilla establishment: an herbivore fish and an herbivore gastropod, both natives; and an invasive non-native shredder fish. Both the isolated and joint effects of these species were evaluated experimentally using treatments that affect differe...
Journal of Applied Ecology, 2008
With biological invasions causing widespread problems in ecosystems, methods to curb the colonization success of invasive species are needed. The effective management of invasive species will require an integrated approach that restores community structure and ecosystem processes while controlling propagule pressure of non-native species. 2. We tested the hypotheses that restoring native vegetation and minimizing propagule pressure of invasive species slows the establishment of an invader. In field and greenhouse experiments, we evaluated (i) the effects of a native submersed aquatic plant species, Vallisneria americana , on the colonization success of a non-native species, Hydrilla verticillata ; and (ii) the effects of H. verticillata propagule density on its colonization success. 3. Results from the greenhouse experiment showed that V. americana decreased H. verticillata colonization through nutrient draw-down in the water column of closed mesocosms, although data from the field experiment, located in a tidal freshwater region of Chesapeake Bay that is open to nutrient fluxes, suggested that V. americana did not negatively impact H. verticillata colonization. However, H. verticillata colonization was greater in a treatment of plastic V. americana look-alikes, suggesting that the canopy of V. americana can physically capture H. verticillata fragments. Thus pre-emption effects may be less clear in the field experiment because of complex interactions between competitive and facilitative effects in combination with continuous nutrient inputs from tides and rivers that do not allow nutrient draw-down to levels experienced in the greenhouse. 4. Greenhouse and field tests differed in the timing, duration and density of propagule inputs. However, irrespective of these differences, propagule pressure of the invader affected colonization success except in situations when the native species could draw-down nutrients in closed greenhouse mesocosms. In that case, no propagules were able to colonize. 5. Synthesis and applications . We have shown that reducing propagule pressure through targeted management should be considered to slow the spread of invasive species. This, in combination with restoration of native species, may be the best defence against non-native species invasion. Thus a combined strategy of targeted control and promotion of native plant growth is likely to be the most sustainable and cost-effective form of invasive species management.
Propagule type influences competition between two submersed aquatic macrophytes
Oecologia, 1989
Glasshouse competition experiments with Hydrilla verticillata (L.f.) Royle indicate that plants grown from turions are weaker competitors than those grown from tubers, when compared to the widely distributed macrophyte, Potamogeton pectinatus L. These results support an earlier hypothesis about the importance of propagule size for predicting the outcome of plant competition . Results of outdoor growth experiments indicate that even though Hydrilla plants from turions are relatively weaker competitors, they are able to grow succesfully in an existing macrophyte bed composed of either, P. pectinatus or P. gramineus. During the early stages of Hydrilla invasion into an area of existing macrophytes, native plants may coexist with Hydrilla. However, once the abundance of Hydrilla tubers in the sediment increases, Hydrilla may displace existing plants.
Scientific Reports, 2018
Propagule pressure is considered a major driver of plant invasion success. Great propagule pressure would enable invasive species to colonize new areas overcoming the resistance of native species. Many highly invasive aquatic macrophytes regenerate from vegetative propagules, but few studies have experimentally investigated the importance of propagule pressure and biotic resistance, and their interaction, in determining invasion success. By manipulating both recipient habitat and the input of vegetative propagules of the invasive seaweed Caulerpa cylindracea in mesocosm, we examined whether higher propagule pressure would overcome the resistance of a native congeneric (Caulerpa prolifera) and influence its performance. With the native, C. cylindracea population frond number decreased irrespectively of pressure level. High propagule pressure did not increase stolon length and single plant size decreased due to the effects of intra-and interspecific competition. Native biomass decreased with increasing C. cylindracea propagule pressure. These results indicate that higher propagule pressure may fail in enhancing C. cylindracea invasion success in habitats colonized by the native species, and they suggest that biotic resistance and propagule pressure co-regulate the invasion process. These findings emphasize the need to preserve/restore native seaweed populations and may help to design effective management actions to prevent further C. cylindracea spread. The invasion of environments by non-native plant species (NNS) is an increasing threat to biodiversity and functioning of ecosystems globally 1,2. Numerous factors may individually affect the establishment of a NNS outside its native range 3,4. Understanding how these factors interact each other to determine the outcome of the invasion process is one of the main goals of ecology, and it is also highly relevant to improving our ability to manage invasive species. The number of propagules (e.g., individuals, seeds, plant fragments) of a NNS entering the new environment, also termed propagule pressure, is considered a major factor of plant invasion success in a wide range of ecosystems 5-7. A large propagule input theoretically would enhance the probability of successful invasion enabling an invader to overcome difficulties related to demographic, environmental or genetic stochasticity of a new location 4,8-10. Relatively few experimental studies, however, have investigated the relationship between propagule pressure and invasion success, and for many plant species it is still unclear whether they may actually gain increasing benefits from increasing propagule pressure 6,11,12. Moreover, the importance of the interaction between propagule pressure and local factors that can affect plant invasion 7,11,13-15 has been rarely tested, especially in aquatic environments 16-20 , probably because of the difficulty in measuring and directly controlling the number of propagules introduced in these environments. Evidence from studies conducted predominantly in terrestrial environments suggests that the nature of interactions between newly arriving species and those already established may play an important role in controlling plant invasion 13,21. For example, the presence of native species capable of exploiting available key resources (such as light, nutrients and space) may inhibit the establishment or limit the spread of an invader once it has established 21-23 (biotic resistance hypothesis). Native congeneric species are expected to be more resistant to NNS invasion based on the conjecture that closely related species have similar resource requirements 24. However, once the invader has established, the impact on the native congeneric may be strong foraging on the same resources.
Acta Botanica Brasilica, 2021
Submersed macrophytes have important ecological roles but non-native invasive species may affect biodiversity and water uses. We investigated the native macrophyte Egeria najas and the invasive Hydrilla verticillata and measured their maximum colonization depth and its relationship with Secchi disk depth, their biomass along the depth gradient and their preferred depths of occurrence. The Itaipu Reservoir was monitored for seven years, during which maximum colonization depth and Secchi disk depth were measured. During a separate sampling, plants were collected to determine biomass along the depth gradient. Ancova showed that the maximum colonization depth of both species increased with increasing Secchi disk depth, but the maximum colonization depth of H. verticillata increased faster with increasing water transparency than did that of E. najas. Quadratic regression revealed that the biomass of each species peaks at intermediate depths. Hydrilla verticillata colonizes deeper regions than does E. najas. The patterns found in the present study can be explained by underwater light and, probably, wave disturbances. The preference of H. verticillata for deeper sites indicates that the ecological niches of the two macrophytes differ, and that H. verticillata has great potential to spread and accumulate biomass in reservoirs.
An analysis of publications on invasive macrophytes in aquatic ecosystems
Aquatic Invasions, 2014
In this study, we performed a scientometric analysis of published scientific papers on the biological invasion of macrophytes in freshwater ecosystems to assess the main trends and gaps in research concerning this group of organisms. The analysis showed that publications on invasive macrophytes increased exponentially in the last decade. However, the activity index (a comparison of the quantitative trends of invasive macrophytes in relation to all of the papers on macrophytes) indicated that invasive macrophytes have not been consistently studied more than other topics in the field of limnology over the last decade. The most studied macrophyte species were Myriophyllum spicatum, Hydrilla verticillata, Phragmites australis and Eichhornia crassipes. Certain gaps were related to the limited number of studies on the important species threatening tropical ecosystems, under-representation of investigations on the impacts of invasive macrophytes on fish and lack of studies associating macrophytes with microorganisms (bacteria and fungi). Studies that encompassed several levels of biological complexity were also scarce, indicating that the studies were fragmented at specific levels. Finally, there was a clear geographical bias, with fewer studies occurring in Neotropical and Afrotropical regions. Identification of these gaps may be useful for addressing future studies that might help evaluate the causes of invasion by macrophytes and the impacts of such invasions on freshwater ecosystems.
Research Article An analysis of publications on invasive macrophytes in aquatic ecosystems
2015
In this study, we performed a scientometric analysis of published scientific papers on the biological invasion of macrophytes in freshwater ecosystems to assess the main trends and gaps in research concerning this group of organisms. The analysis showed that publications on invasive macrophytes increased exponentially in the last decade. However, the activity index (a comparison of the quantitative trends of invasive macrophytes in relation to all of the papers on macrophytes) indicated that invasive macrophytes have not been consistently studied more than other topics in the field of limnology over the last decade. The most studied macrophyte species were Myriophyllum spicatum, Hydrilla verticillata, Phragmites australis and Eichhornia crassipes. Certain gaps were related to the limited number of studies on the important species threatening tropical ecosystems, under-representation of investigations on the impacts of invasive macrophytes on fish and lack of studies associating macr...
2019
The deposition of plant detritus changes sediment features, but little is known about how the accumulation of detritus affects the colonization of invasive and native submerged macrophytes. We tested the predictions that (i) submerged macrophyte occurrences correlate positively with the presence of detritus over sediment; (ii) the colonization of submerged macrophytes increases in the presence of detritus; (iii) the invasive macrophyte Hydrilla verti-cillata grows faster than the native macrophyte Egeria najas independent of the presence of detritus and (iv) E. najas is affected by competition with H. verticil-lata, and competition is mediated by the presence of detritus. We evaluated the co-occurrences of submerged macrophytes and detritus in situ and experimentally tested the effects of detritus on submerged macrophyte growth with and without competition. The presence of submerged macrophytes and detritus was negatively correlated in situ. Our experiments indicate that the detritus of emergent macrophytes, including invasive macrophytes, enhances nutrients after reflooding and increases the early growth of submerged macrophytes but does not influence the outcome of competition. Thus, the facilitation of invasive success at the beginning of detritus decomposition (indicated by our experiments) may be counteracted by negative effects after a long decomposition period (indicated by our field data).
Aquatic Ecology, 2012
The propagation of most aquatic macrophytes occurs vegetatively, via fragments. After dispersal, the fragments may exhibit two survival strategies: colonization (the ability to develop roots) and regeneration (the ability to develop new propagules that can disperse). Invasive species, for example, Hydrilla verticillata, are known to have a high potential for dispersal and growth. We experimentally evaluated the colonization and regeneration abilities and growth rates of this species in the early stage of development and compared these properties to the corresponding characteristics of two native species of Hydrocharitaceae (Egeria densa and Egeria najas). The following hypotheses were tested: (1) fragments with apical tips have greater colonization and regeneration abilities and higher growth rates than fragments without apical tips and (2) H. verticillata has greater colonization and regeneration abilities and higher growth rates than other native species of Hydrocharitaceae. Our results showed that both types of fragments had the same ability to colonize, whereas fragments without tips had a higher ability to regenerate. However, fragments with apical tips showed higher growth rates. It is probable that these higher growth rates resulted from apical dominance. H. verticillata had the greatest propagation potential. Its colonization and regeneration abilities and growth rates were greater than those of the native species. These differences can produce competitive advantages for the exotic species in the early stages of development in new habitats and may contribute to understanding the success of the exotic compared to the native species.
The invasive submerged macrophyte Hydrilla verticillata as a foraging habitat for small-sized fish
Natureza & Conservação, 2014
Paraná River A B S T R A C T Several species of aquatic macrophytes have invaded ecosystems outside their ranges, producing a variety of impacts on native biota. In this study, we tested the role of the invasive macrophyte Hydrilla verticillata as a foraging habitat for small fish species. To achieve this goal, we assessed the feeding activity and diet composition of fish captured in patches of the invasive H. verticillata and of a similar native macrophyte (Egeria najas). Feeding activity did not differ significantly between H. verticillata and E. najas, indicating that foraging activity was not affected. However, differences in diet composition were significant in three out of five fish species and marginally significant in one species, suggesting that the invasive and native macrophytes provide different types of food resources for fish. Thus, although H. verticillata does not affect the foraging activity, it has the potential to affect the assemblages of small-sized fish through changes in the proportions of food resources.