Differences in life history strategies between an invasive and a competing resident seed predator (original) (raw)
Related papers
Ecosphere, 2020
Successful invasive species are often closely related to other invasive species, suggesting that shared traits contribute to their invasion success. Alternatively, related species can differ in invasiveness, where some are highly invasive yet congeners seem unable to invade. Here, we compared the traits and establishment abilities of two highly successful invasive species, Gambusia affinis and G. holbrooki, to those of two close relatives, G. geiseri and G. hispaniolae. Using laboratory experiments, we compared lowtemperature tolerances and life histories of the four species. In a semi-natural mesocosm experiment, we simulated the invasion of standardized, simple pond communities and examined the effects of these traits on each species' ability to become established. The invasive species, G. affinis and G. holbrooki, were more tolerant of low-temperature stress, had greater fecundities, higher growth rates, and reached maturity sooner than G. geiseri and G. hispaniolae. In mesocosms, the invasive Gambusia exhibited higher intrinsic growth rates and carrying capacities and thus achieved and maintained larger populations than the two congeners. Only G. affinis and G. holbrooki successfully established long-term populations in these experimental communities. G. geiseri and G. hispaniolae failed to establish as a result of 100% overwintering mortality. These results support the notion that the ability of invaders to cope with the abiotic conditions of target communities has a major effect on whether establishment occurs, while life histories play an important secondary role. Our results showed that invasiveness is likely not a trait of the entire genus Gambusia.
Biological Invasions, 2000
The seeds of both cedar-of-Lebanon (Cedrus libani) and Cyprus cedar (Cedrus brevifolia) are attacked in their natural range by a specialised chalcid, Megastigmus schimitscheki. From 1995 to 1999, seeds were screened for insect damage in the main cedar plantations of southern France, as well as in the stands where cedar is mixed with firs (Abies spp.). X-rays were used to identify chalcid-infested seeds from which the insects were then reared. The surveys revealed the presence of M. schimitscheki in all the stands of Atlas cedar, Cedrus atlantica, planted at Mt Ventoux, southeastern France. The chalcid also infested seeds of an exotic fir, Abies pinsapo, planted in the same area. However, it has not yet reached the cedar plantations in southwestern France, where the seeds are colonised by a related exotic insect, Megastigmus pinsapinis, originating from North Africa. The latter species was common in cedar seeds at Mt Ventoux in the early 1990s but seems to have been supplanted by M. schimitscheki in the invasion zone. A native chalcid species, Megastigmus suspectus, was also shown to have shifted to a slight extent from a native fir, A. alba, onto cedar. The presence of three chalcid species competing for cedar seed resources may result in a substantial decline of the regeneration potential of that tree species. At Mt Ventoux, up to 92.6% of the cedar seeds were attacked, with 86.8% due to M. schimitscheki. The survey also revealed the widespread presence of another North American chalcid, Megastigmus rafni, in the fir stands of southern France.
2010
ABSTRACT This paper describes the reproductive characteristics of 93 neophytes (alien species introduced after 1500 A.D.) of the flora of the Czech Republic and compares trait values between naturalized inva-sive and naturalized non-invasive neophytes. Species were sampled and seed collected in the field from multiple localities in the Czech Republic. Traits related to seed production (propagule number per plant and per population), dispersal (propagule size, length/width ratio and weight; buoyancy; epizoochory; terminal velocity) and establishment (germination; seedling relative growth rate; seedling establishment) were measured for each species either in the field, in a common garden experiment or in the laboratory. Invasive species significantly differ from naturalized non-invasive species in propagule length/width ratio (by having lower ratio, i.e. more rounded propagules) and fecundity (invasive species are more fecund, both per individual plant and in terms of the population propagule production). Invasive species have proportionally fewer seedlings establishing in the autumn and better capacity for dispersal by wind than non-invasive species. The results for several traits differ depending on whether or not the effect of phylogeny is included in analytical models. Considering species relatedness expressed as a taxonomic hierarchy, invasive species have lighter propagules and higher population propagule numbers, and marginally significantly differ in produc-ing more propagules per plant and having higher capacity for dispersal by water. We found that most variation in invasiveness is linked to variation among species within genera. This distribution of relatedness means that predictions of whether a species will become invasive cannot be based on traits of the relatives of the given species at higher taxonomic levels. The distinction made in this paper, i.e. invasive species vs. naturalized but non-invasive species, can potentially contribute to a deeper understanding of the role of traits associated with invasiveness because the crucial transi-tion from the naturalized to invasion stage is rarely addressed in invasion ecology.
Biological Invasions, 2013
Acanthoscelides macrophthalmus is a seed predator that has become widely distributed along with its native host, Leucaena leucocephala (Mimosoideae), which is a neotropical leguminous tree and one of the most invasive plants worldwide. Previous studies revealed that A. macrophthalmus is able to host-shift to several mimosoid species. Here, we aim to test the host-shift potential to other mimosoid and nonmimosoid plants and possible roles of interspecific competition, genetic background, and plant chemistry in host-shift. First, we found that A. macrophthalmus predator completed development on two new hosts: pigeon pea Cajanus cajan and Cajanus scarabaeoides (Faboideae), by rearing from seeds collected in South/ Southeast Asia and Hawaii. In contrast, in most regions, both Cajanus species were infested only by other beetle species. Second, we performed no-choice tests using 11 leguminous plants, covering all three subfamilies as potential hosts, including the two new hosts. A Taiwanese A. macrophthalmus population reared in the laboratory on Leucaena did not deposit eggs on any of the seeds of each tested species. To compare host-shift responses between populations, we also used a Hawaiian A. macrophthalmus population that had completed its development on freshly M. Tuda, L.-H. Wu and N. Yamada have equally contributed to this study.
Plant Ecology
Although closely related, Impatiens glandulifera and Impatiens balfourii differ in their invasiveness in Europe; only the former is highly invasive there. Following the assumptions of the enemy release hypothesis (ERH), we tested whether these differences may be explained by the levels of seed infestation by pathogenic fungi. Using seeds collected along the Swiss-Italian border, we recorded four true pathogens of seeds: Fusarium culmorum, F. oxysporum, F. sporotrichoides, and Giberella avenacea. In Italy the seeds of I. balfourii were infected by fungal pathogens more often than those of I. glandulifera, while in Switzerland both species were under the same level of pressure. However, the overall differences in pathogen abundance were consistent with the ERH: seeds of the more invasive species were attacked less. This could be a result of differences between the communities of fungal pathogens attacking the seeds of both species in each country. The number of colonies of secondary pathogens (Cladosporium cladosporioides, Alternaria alternata) correlated negatively with the number of colonies of true pathogens; we suggest that the secondary pathogens may have prevented the occurrence of the true pathogens. The reason for the between-country differences in the fungal pathogen communities is unclear. A possible explanation is that Italy and Switzerland differ in their road and greenarea maintenance work schemes, which may have influenced pathogen pressure on seeds. This study is one of the few that offers results indicating that release from enemies may be crucial to the invasion success of plants as early as the seed stage. Keywords Biological invasions Á Seed enemies Á Seedborne fungi Á Seed antagonists Á Obligatory pathogens Á Enemy release hypothesis Communicated by Timothy Bell.
Molecular ecology, 2012
Most invasive species established in Europe originate from either Asia or North America, but little is currently known about the potential of the Anatolian Peninsula (Asia Minor) and/or the Near East to constitute invasion sources. Mediterranean forests are generally fragile ecosystems that can be threatened by invasive organisms coming from different regions of the Mediterranean Basin, but for which historical data are difficult to gather and the phylogeographic patterns are still poorly understood for most terrestrial organisms. In this study, we characterized the genetic structure of Megastigmus schimitscheki, an invasive seed-feeding insect species originating from the Near East, and elucidated its invasion route in South-eastern France in the mid 1990s. To disentangle the evolutionary history of this introduction, we gathered samples from the main native regions (Taurus Mountains in Turkey, Lebanon and Cyprus) and from the invaded region that we genotyped using five microsatell...