Estimating the invasion success of introduced plants

We present methods for estimating the base proportion of introduced alien species that will naturalize, and the distribution of time until naturalization occurs. The approach is Bayesian, incorporating prior estimates of the probability of naturalization and the time from introduction to naturalization. A worked example uses data on the introduction and time to recorded naturalization of woody perennials introduced to South Australia. Up until 2007, 188 of 2230 (8.4%) woody perennials listed in nursery catalogues between 1843 and 1985 were recorded as having naturalized. If prior information on naturalization rates from elsewhere is ignored, the available data suggest that the most likely proportion of introduced plants that will naturalize is large (0.93) though uncertain (95% CI 0.51–0.99), with the corresponding mean time to recorded naturalization being protracted (522 years) and similarly uncertain (95% CI 360–678 years). Alternatively, if informative prior estimates of both the naturalization probability and the time to recorded naturalization are incorporated, the most likely probability of naturalization is estimated to be 18.6% (95% CI 15.5–23.4%). For those plants that do naturalize, the most likely value for the mean time from importation to recorded naturalization is 149 years (95% CI 130–174 years). Our results illustrate the potentially long timescale of the naturalization process, and the challenges this presents for obtaining accurate estimates of naturalization parameters.     

Resident plant diversity and introduced earthworms have contrasting effects on the success of invasive plants

Theoretical predictions and empirical studies suggest that resident species diversity is an important driver of community invasibility. Through trait-based processes, plants in communities with high resident species diversity occupy a wider range of ecological niches and are more productive than low diversity communities, potentially reducing the opportunities for invasion through niche preemption. In terrestrial plant communities, biotic ecosystem engineers such as earthworms can also affect invasibility by reducing leaf litter stocks and influencing soil conditions. In a greenhouse experiment, we simultaneously manipulated resident species diversity and earthworm presence to investigate independent and interactive effects of these two variables on the success of several invasive plants. Higher diversity of resident species was associated with lower biomass of invasives, with the effect mediated through resident species biomass. The presence of earthworms had a strong positive effect on the biomass of invasive species across all levels of resident species diversity and a weaker indirect negative effect via decreased soil moisture. Earthworms also weakened the positive correlation between resident species diversity and productivity. We did not observe any interactive effects of resident species biomass and earthworms on invasive species success. Partitioning the net biodiversity effect indicated that selection effects increased with resident species diversity whereas complementarity effects did not. Results suggest that managing for diverse forest communities may decrease the susceptibility of these communities to invasions. However, the presence of introduced earthworms in previously earthworm-free sites may undermine these efforts. Furthermore, future studies of plant community invasibility should account for the effects of introduced earthworms.     

Infanticide in the evolution of reproductive synchrony: effects on reproductive success

Synchronous breeding in animals and plants has stimulated both a theoretical and empirical examination of the possible benefits of active synchronization. The selective pressures of predation and infanticide are the strongest candidates proposed to explain the evolution of reproductive synchrony. Alternatively, breeding asynchronously with conspecifics may ensure a greater availability of resources per breeder. However, the possible fitness benefits resulting from active asynchronization have not yet received attention in evolutionary ecology. Here we present a hypothesis, based on a graphical model, illustrating the costs and benefits of the two modes of reproduction. We tested the hypothesis empirically using a 2 x 2 full factorial study design, where reproductive synchrony and infanticide tactics were manipulated in enclosed populations of the bank vole. The results reveal a relationship between infanticide tactics and breeding synchrony as illustrated by our hypothesis. In general, female reproductive success (number and size of offspring surviving to weaning) was significantly lower in infanticidal populations. Moreover, an asynchronous breeding pattern proved to be advantageous in the noninfanticidal population but this advantage of asynchrony was lost as infanticide became common in the population. Our findings support the idea that synchronous reproduction could have evolved as a counterstrategy against infanticide.     

Invasion of an exotic forb impacts reproductive success and site fidelity of a migratory songbird

Although exotic plant invasions threaten natural systems worldwide, we know little about the specific ecological impacts of invaders, including the magnitude of effects and underlying mechanisms. Exotic plants are likely to impact higher trophic levels when they overrun native plant communities, affecting habitat quality for breeding songbirds by altering food availability and/or nest predation levels. We studied chipping sparrows (Spizella passerina) breeding in savannas that were either dominated by native vegetation or invaded by spotted knapweed (Centaurea maculosa), an exotic forb that substantially reduces diversity and abundance of native herbaceous plant species. Chipping sparrows primarily nest in trees but forage on the ground, consuming seeds and arthropods. We found that predation rates did not differ between nests at knapweed and native sites. However, initiation of first nests was delayed at knapweed versus native sites, an effect frequently associated with low food availability. Our seasonal fecundity model indicated that breeding delays could translate to diminished fecundity, including dramatic declines in the incidence of double brooding. Site fidelity of breeding adults was also substantially reduced in knapweed compared to native habitats, as measured by return rates and shifts in territory locations between years. Declines in reproductive success and site fidelity were greater for yearling versus older birds, and knapweed invasion appeared to exacerbate differences between age classes. In addition, grasshoppers, which represent an important prey resource, were substantially reduced in knapweed versus native habitats. Our results strongly suggest that knapweed invasion can impact chipping sparrow populations by reducing food availability. Food chain effects may be an important mechanism by which strong plant invaders impact songbirds and other consumers.     

Breeding timed to maximize reproductive success for a migratory songbird: the importance of phenological asynchrony

Phenological advances and trophic mismatches are frequently reported ecological consequences of climate warming. Trophic mismatches occur when phenological responses to environmental conditions differ among trophic levels such that the timing of resource demand by consumers becomes decoupled from supply. We used 25 years of demographic measurements of a migratory songbird (the black‐throated blue warbler Setophaga caerulescens) to compare its breeding phenology to the phenology of both its caterpillar prey and the foliage on which caterpillars feed. Caterpillar biomass in this forest did not show a predictable seasonal pulse. Nest initiation by warblers in this northern hardwood forest was therefore not timed to coincide with a peak in food availability for nestlings. Nonetheless, timing of first clutches was strongly associated with spring leaf expansion (slope ± SE = 0.56 ± 0.08 days per day of change in leaf phenology, R² = 0.66). Warblers adjusted the timing of breeding to early springs mainly by shortening the interval between arrival and clutch initiation, but this likely has limits because recent early springs are approaching the relatively inflexible dates when birds arrive on the breeding grounds. Although the timing of first nests did not match 1:1 with leaf‐out phenology, the adjustments in breeding time maximized mean annual reproductive success. Nest predation had the greatest effect on annual reproductive success, but the ability of nesting warblers to appropriately track leaf phenology accounted for effects on annual reproductive success comparable to the influence of variation in caterpillar abundance and conspecific density. Nesting phenology in black‐throated blue warblers was generally well matched to the timing of leaf‐out, even though the match was not 1:1. Without measurements of reproductive success, these unequal phenological shifts might otherwise have been interpreted as having negative ecological consequences.     

Some effects of mastectomy on reproductive success in the guinea-pig

Virgin guinea-pigs were mastectomized in two stages between 11 and 18 weeks of age and then mated, starting 19 weeks after final surgery. In the subsequent first pregnancy, the incidence of still-births and neonatal deaths was significantly higher in the mastectomized animals (6 out of 12 mothers (50%) and 14 out of 49 young (29%) compared with intact guinea-pigs (1 out of 15 mothers (7%) and 1 out of 58 young (2%)). There was no significant effect of mastectomy on litter size and weight or on gestation period. The still-born were not significantly different in weight from those born alive. A significant relation was found between maternal weight changes in the period 20 to 5 days before parturition and the occurrence of still-births and neonatal deaths; still-births were associated with a period of reduced weight gain. No effect of mastectomy on the length of the oestrous cycle was apparent but a significant increase in the incidence of non-pregnancy was found. The results provide further evidence that mastectomy influences reproductive success in the guinea-pig and suggest that parturition is a key process affected.     

The influence of parental relatedness on reproductive success

The relationship between fitness and parental similarity has been dominated by studies of how inbreeding depression lowers fecundity in incestuous matings. A widespread implicit assumption is that adult fitness (reproduction) of individuals born to parents who are not unusually closely related is more or less equal. Examination of three long-lived vertebrates, the long-finned pilot whale, the grey seal and the wandering albatross reveals significant negative relationships between parental similarity and genetic estimates of reproductive success. This effect could, in principle, be driven by a small number of low quality, inbred individuals. However, when the data are partitioned into individuals with above average and below average parental similarity, we find no evidence that the slopes differ, suggesting that the effect is more or less similar across the full range of parental similarity values. Our results thus uncover a selective pressure that favours not only inbreeding avoidance, but also the selection of maximally dissimilar mates.     

Divergent effects of leaf-cutting ant herbivory and soil engineering on the reproductive success of plants in a Caatinga dry forest

相似文献   

The reproductive success of wealthy Americans

The reproductive success of a sample of wealthy Americans exceeds that of the general U.S. population. These Americans have more children than do their age-matched counterparts, and the survivorship of these children is very high. These wealthy Americans appear equally likely to have sons as to have daughters.     

Impacts of nest predators and weather on reproductive success and population limitation in a long‐distance migratory songbird

Although avian nesting success is much studied, little is known about the relative importance of the factors that contribute to annual reproductive success and population limitation, especially for long‐distance migratory songbird species. We combined a field experiment limiting access to nests by mammalian predators with modeling of long‐term field data of American redstarts (Parulidae: Setophaga ruticilla) to assess the effects of multiple environmental variables on breeding success and population limitation. Experimental treatment (baffles placed around tree boles beneath active nests; n = 71) increased nesting success of this single‐brooded species significantly (77 vs 50% in controls; n = 343), demonstrating that scansorial mammals, primarily red squirrels Tamiasciurus hudsonicus and eastern chipmunks Tamias striatus, reduced reproductive success. Based on unbaffled nests (n = 466), daily nest survival varied annually, and was positively influenced by May temperature and negatively by sciurid nest predator abundance. Daily nest survival was also influenced positively by June rainfall, and declined with nest age but not with calendar date. Since nest failure was overwhelmingly caused by nest predation, these significant climate and nest‐age effects in our models are indirect, likely influencing nest predator and/or nesting bird behaviors that in turn influenced nest predation. Redstart population density had no effect on nesting success, after accounting for other factors. Annual reproductive success accounted for 34% of the variability in annual population change in redstarts in our study area. Our findings document 1) breeding season population limitation in this species, 2) a link between tree masting and bird population dynamics via mammal population fluctuations, 3) the independent contributions of summer versus winter population processes in a migratory species, and 4) the potential complexity of climate‐biotic interactions.     

The effects of a bumble bee nectar robber on plant reproductive success and pollinator behavior

Interactions between a plant species (Corydalis caseana), a bumble bee nectar robber (Bombus occidentalis), and a bumble bee pollinator (B. appositus) were studied. There were no significant differences between naturally robbed and unrobbed flowers in fruit set or mean seed set per fruit. Plots of C. caseana plants were subjected to treatments of robbing and no robbing using commercially available colonies of B. occidentalis. Robbers did not pollinate the flowers. Pollinator behavior was observed to determine (1) the number of bees attracted to each plot, (2) the number of inflorescences visited in a plot, (3) the number of flowers visited on each inflorescence, and (4) the distance flown between inflorescences. There were no significant differences in the number of inflorescences visited per bee or the number of flowers visited per inflorescence per bee when robbed and unrobbed treatments were compared. Of the parameters measured, only distance flown between inflorescences differed in the robbed and the unrobbed treatments. Bees flew significantly further between inflorescences in the robbed plots than in the unrobbed plots. The results indicate that the nectar robbers have no negative effect on fruit set or seed set in C. caseana and that they may cause increased pollen flow distances by changing the behavior of the pollinator.     

Indices of reproductive skew depend on average reproductive success

Several indices of reproductive skew, which quantify the degree of unequal partitioning of reproductive output among members in an animal society, have been proposed. Here we point out the drawbacks of these indices. The most serious problem is the dependence of the indices on mean reproductive success: skew values tend to be larger, as average numbers of offspring decrease, due to random sampling error in numbers of offspring. Thus it is difficult to compare societies with different average lifetime reproductive success using these indices, even though we have presented methods to calculate the expected reproductive skew caused by random sampling error, especially when average numbers of offspring are small, as is often the case with cooperatively breeding vertebrates. As an alternative, we propose using the spatial dispersion indices of population ecology (Morisita's index or its standardized version) for the measurement of reproductive skew. These indices are almost independent of average fecundity and have their own method of testing for random variation in offspring numbers. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of residential ecology on patterns of child work and mother's reproductive success among Indo-Fijians

A central question in human life history theory surrounds the rapid pace of reproduction of human mothers. Accordingly, evolutionary anthropologists have debated who provides assistance to human mothers and how. Here, we develop an embodied capital framework (i.e., a parental investment strategy focused on improving the adult productivity of offspring) to understand urban–rural differences in the extent to which children help to underwrite the costs of their dependence among Indo-Fijians. We employ multiple regression analysis to explore the relationships among various categories of helpful activity, residential ecology and mother's reproductive success and show that, while rural children work more overall compared to urban children, childcare is the only productive activity with any relationship to mother's reproductive success. We conclude by providing support for the general idea that children are potentially important sources of allomaternal help, but emphasize the need for more nuanced models of how such help is provided.     

Testing common assumptions in studies of songbird nest success

We studied Ovenbird Seiurus aurocapilla and Golden‐winged Warbler Vermivora chrysoptera populations in northern Minnesota, USA, to test two common assumptions in studies of songbird nest success: (1) that the condition of an empty nest on or near its expected fledge date is an indicator of nest fate; and (2) that the presence of a fledgling or family group within a territory confirms a successful nest in that territory. We monitored the condition of nests and used radiotelemetry to monitor juveniles through the expected fledging date and early post‐fledging period. Of nests that contained nestlings 1–2 days before the expected fledge date, fates were misidentified using nest condition alone for 9.5% of Ovenbird nests, but those misidentifications were made in both directions (succeeded or failed), yielding only a small bias in estimated nest success. However, 20% of Golden‐winged Warbler nests were misidentified as successful using nest condition during the final visit interval, biasing the nest success estimate upward by 21–28% depending on the treatment of uncertain nest fates. Fledgling Ovenbirds from 58% of nests travelled beyond their natal territory within 24 h, rising to 98% after 5 days, and those fledglings travelled up to 390 m from nests within 10 days of fledging. Fledgling Golden‐winged Warblers from 13% of nests travelled beyond their natal territory within 24 h, rising to 85% after 5 days, and those fledglings travelled up to 510 m from nests within 10 days of fledging. We conclude that nest condition and fledgling presence can be misleading indicators of nest fate, probably commonly biasing nest success estimates upward, and we recommend that these assumptions should be tested in additional species.     

A meta-analysis of impacts of alien vs. native plants on pollinator visitation and reproductive success of co-flowering native plants

Alien plant species can alter pollinator visitation and, in turn, the sexual reproduction of natives. Using a conventional and a phylogenetically controlled meta-analytical approach on a data set of 40 studies, we evaluated the effect of alien neighbour plant species (aliens) on visitation to and reproduction of native co-flowering focal species (focals), and compared such effect to that of native neighbours (natives). An overall significantly negative effect of aliens on visitation to and reproduction of focals was confirmed. Interestingly, aliens differed from natives in their effect on visitation, but not on reproductive success. The negative effect of aliens on visitation and reproductive success increased at high relative alien plant abundance, but this increase was proportionally lower than the increase in relative plant abundance. Likewise, effect of aliens on visitation and reproductive success was most detrimental when alien and focal species had similar flower symmetry or colour. The phylogenetic relatedness between alien neighbours and focals influenced the reproductive success effect size. Results of the phylogenetic meta-analysis were only partly consistent with those of the conventional meta-analysis, depending on the response variable and on whether we controlled for the phylogeny of neighbour or focal species, which calls for special attention to control for species relatedness in this type of review. This study demonstrates the predominant detrimental impact of alien plants on pollination and reproduction of natives, and highlights the importance of phenotypic similarity to the outcome of the interaction.     

Florally rich habitats reduce insect pollination and the reproductive success of isolated plants

Landscape heterogeneity in floral communities has the potential to modify pollinator behavior. Pollinator foraging varies with the diversity, abundance, and spatial configuration of floral resources. However, the implications of this variation for pollen transfer and ultimately the reproductive success of insect pollinated plants remains unclear, especially for species which are rare or isolated in the landscape. We used a landscape‐scale experiment, coupled with microsatellite genotyping, to explore how the floral richness of habitats affected pollinator behavior and pollination effectiveness. Small arrays of the partially self‐compatible plant Californian poppy (Eschscholzia californica) were introduced across a landscape gradient to simulate rare, spatially isolated populations. The effects on pollinator activity, outcrossing, and plant reproduction were measured. In florally rich habitats, we found reduced pollen movement between plants, leading to fewer long‐distance pollination events, lower plant outcrossing, and a higher incidence of pollen limitation. This pattern indicates a potential reduction in per capita pollinator visitation, as suggested by the lower activity densities and richness of pollinators observed within florally rich habitats. In addition, seed production reduced by a factor of 1.8 in plants within florally rich habitats and progeny germination reduced by a factor of 1.2. We show this to be a consequence of self‐fertilization within the partially self‐compatible plant, E. californica. These findings indicate that locally rare plants are at a competitive disadvantage within florally rich habitats because neighboring plant species disrupt conspecific mating by co‐opting pollinators. Ultimately, this Allee effect may play an important role in determining the long‐term persistence of rarer plants in the landscape, both in terms of seed production and viability. Community context therefore requires consideration when designing and implementing conservation management for plants which are comparatively rare in the landscape.     

Human-induced eutrophication enhances reproductive success through effects on parenting ability in sticklebacks

Human-induced processes are altering habitats at an unprecedented rate and scale. This has changed the biodiversity and biomass in many areas, but also led to phenotypic and genetic alterations of populations. Here we investigated the effects of the ongoing eutrophication in the Baltic Sea on the reproductive success of threespine stickleback males Gasterosteus aculeatus , through effects on reproductive behaviour and parenting ability. We allowed males to complete breeding cycles in a competitive setting under increased macro algae cover or increased turbidity caused by phytoplankton growth. Both environmental factors improved the parenting ability of the males and enhanced reproductive output. Increased alga growth and turbidity reduced aggressive interactions between males during the parental phase, probably due to reduced visibility, which slowed down a deterioration of condition. This increased the reproductive lifespan of the males and enabled them to complete more breeding cycles, as found when males were allowed to complete as many breeding cycles as they could under increased algae cover. In addition, increased turbidity improved oxygen conditions, which enhanced hatching success and reduced the need for vigorous fanning behaviour. Increased turbidity, however, relaxed selection on male size. Together with earlier results on relaxed sexual selection under changed environmental conditions, this suggests that the effect of eutrophication on stickleback populations is complex. It increases the reproductive output of populations, since more individuals are spawning within eutrophicated areas and their hatching success is increased, but it relaxes sexual and natural selection at the reproductive stage. Whether this will shift selection and population regulation to other life stages, such as the juvenile stage, deserves further investigations.     

Criteria of reproductive success

To determine reproductive success, it is necessary for the researcher to specify a criterion of success, such as the number of a parent's offspring living to the age of reproduction. A measurement model, which includes the researcher's choice of criterion, has been proposed to estimate the lifetime reproductive success (R) of long-lived animals from complete or incomplete knowledge of the reproductive life histories of mothers and the survival fates of offspring. This research uses R and data from female baboons of Mikumi National Park, Tanzania, as vehicles to investigate the relationship between reproductive success and several criteria. Secondarily, it also investigates the relationship between R and the number and rate of offspring production. Seven criteria of reproductive success, ranging in 12-month increments from 0 (birth) to 72 months of offspring life, were applied to 10.5 years of reproductive data from 61 Mikumi females. Theoretically, the best scenario for comparative purposes is an invariant R across different criteria; however, the mean R systematically increased as the criteria increased. This is more an inconvenience than a serious problem because high correlations indicate high predictability between Rs from pairs of criteria. R was modestly correlated with the rate of offspring production, indicating that rate can be employed as a rough index of reproductive success. The choice of a criterion is a trade off between theory, practicality, the strength of the criterion, and the effect of the choice upon sample representativeness and size. Am. J. Primatol. 41:87–101, 1997. © 1997 Wiley-Liss, Inc.