Larger Propagules Research Articles

To disperse or compete? Coevolution of traits leads to a limited number of reproductive strategies

Reproductive strategies are defined by a combination of behavioural, morphological, and life‐history traits. Reproductive investment and offspring propagule size are two key traits defining reproductive strategies. While a substantial amount of work has been devoted to understanding the independent fitness effects of each of these traits, it remains unclear how coevolution between them ultimately affects the evolution of reproductive strategies, and how this might influence the relationship between dispersal and environmental factors. In this study we explore how the evolution of reproductive strategies defined by these two coevolving traits is influenced by resource availability and spatial structuring of the environment using a simulation model. We find three possible equilibrium strategies across all scenarios: a competitor strategy with high reproductive investment (producing large propagules which disperse short distances), and two coloniser strategies differing in reproductive investment (both producing small propagules which disperse long distances). The possible equilibrium strategies for each scenario depended on starting conditions, spatial structure and resource availability. Evolutionary transitions between these equilibrium strategies were more likely in heterogeneous than homogeneous landscapes and at higher resource levels. Transition from coloniser strategy to competitor strategy was usually a two‐step process, with changes in propagule size following initial evolution in investment. This highlights how the interaction between the two trait axes affects the evolution of reproductive strategies, particularly where fitness valleys preclude the simultaneous evolution of traits. Our results highlight the need to incorporate trait coevolution into evolutionary models to help develop a more integrative understanding of the structure of natural populations and how the interaction between traits constrains or hinders evolutionary processes.

SHORT NOTE Propagation of Bambusa vulgaris: a simplified method for use in display glasshouses

Horticulture staff at the Royal Botanic Garden Edinburgh have experimented with the propagation of Bambusa vulgaris by planting pieces of stem directly into the bed in which the plant is to grow. The success of the method means that both transportation time and space are saved by removing the stage where these large propagules are in the propagation unit.

Effects of Seasonality and Climate on the Propagule Deposition Patterns of the Chestnut Blight Pathogen Cryphonectria parasitica in Orchards of the Alpine District of North Western Italy

Chestnut blight is the major disease of chestnuts (Castanea spp.) cultivated worldwide for the production of edible nuts. The disease is caused by the pathogenic fungus Cryphonectria parasitica, which infects trees by means of airborne propagules penetrating through fresh wounds on stems and branches. The aims of this study were to (I) assess the temporal propagule deposition patterns of C. parasitica in the Alpine district of North Western Italy, (II) test and model the effects of seasonality and climate on the above patterns, and (III) investigate the spatial distribution of propagule deposition at the within-site scale. A two-year-long spore trapping experiment was conducted in three chestnut orchards. Approximately 1300 samples were collected and processed with a species-specific qPCR assay to quantitatively assess the propagule deposition of C. parasitica. Results showed that C. parasitica can release propagules all over the year, though with significant seasonal peaks in the spring and fall (p < 0.05). Large propagule loads were significantly correlated (p < 0.05) with an increasing number of rainy days of the week (days providing 1–10 mm/day of water). Models predicting periods at high risk of infection based on climate and seasonality were fitted and successfully validated (p < 0.05).

Trait divergence between endemic plants of Aegean islands and their widespread congeners

Evolutionary processes on islands, and the attributes of rare plant species restricted to islands have received increasing attention in the last decade, but most of the evidence comes from oceanic archipelagos while continental islands have been much less studied. We test if narrow endemic species of Aegean islands (E Mediterranean region) have evolved particular trait values and ecological attributes. In 64 pairs of congeneric species i.e., an island endemic and a congeneric widespread species, we compared morphological traits (both vegetative and reproductive), and altitudinal range using a phylogenetically constrained multilevel model. Island endemics had larger propagules, larger petals, shorter stems, shorter flowering duration, and they occupied a narrower altitudinal range. The results are interpreted in terms of lower competitive ability and lower dispersal capacity in Aegean endemics. Larger corolla could be accounted for by competition for pollinators in insect-rich ecosystems. Field observations are needed to test if island endemics and their widespread congeners occupy distinct niches when in sympatry on the same island.

Propagule size and sex ratio influence colonisation dynamics after introduction of a non-native lizard.

The composition of founding populations plays an important role in colonisation dynamics and can influence population growth during early stages of biological invasion. Specifically, founding populations with small propagules (i.e. low number of founders) are vulnerable to the Allee effect and have reduced likelihood of establishment compared to those with large propagules. The founding sex ratio can also impact establishment via its influence on mating success and offspring production. Our goal was to test the effects of propagule size and sex ratio on offspring production and annual population growth following introductions of a non-native lizard species (Anolis sagrei). We manipulated propagule composition on nine small islands, then examined offspring production, population growth and survival rate of founders and their descendants encompassing three generations. By the third reproductive season, per capita offspring production was higher on islands seeded with a relatively large propagule size, but population growth was not associated with propagule size. Propagule sex ratio did not affect offspring production, but populations with a female-biased propagule had positive growth, whereas those with a male-biased propagule had negative growth in the first year. Populations were not affected by propagule sex ratio in subsequent years, possibly due to rapid shifts towards balanced (or slightly female biased) population sex ratios. Overall, we show that different components of population fitness have different responses to propagule size and sex ratio in ways that could affect early stages of biological invasion. Despite these effects, the short life span and high fecundity of A. sagrei likely helped small populations to overcome Allee effects and enabled all populations to successfully establish. Our rare experimental manipulation of propagule size and sex ratio can inform predictions of colonisation dynamics in response to different compositions of founding populations, which is critical in the context of population ecology and invasion dynamics.

SEEDLING AND GROWTH OF Rhizophora mangle L. PROPAGULES AT A RESTORATION SITE (APA DE GUAPI-MIRIM - RJ)

One of the biggest mangrove forests in Rio de Janeiro is located at Guanabara Bay. However, a large part of this ecosystem is currently suppressed and only 1/3 of the original 261.90 km² of mangrove vegetation can be observed. Thus, several conservation and management actions are conducted in this ecosystem. Studying plantations and other restoration strategies for this biome is important to understand the dynamics of this ecosystem and enhance such strategies. Size can be one of the most important characteristics for propagules success. Some studies state that larger seedlings can resist more and have greater survival than smaller seedlings. Therefore, this study aims to analyze the germination and development of Rhizophora mangle L. propagules at an in situ plantation in the mangroves of the Guapi-Mirim Environmental Protection Area. A total of nine plots were delimited with spacing of 4 meters by 1 meter each in which Rhizophora mangle propagules were separated into small and large groups and planted. Their germination and development were subsequently monitored for a period of 6 months. The diameter, height and initial weight of the propagules and the increase in height and diameter at 76, 93 and 154 days after planting were measured. Periodic observations were made approximately every 20 days in order to quantify the rate and type of mortality (predation, water current carriage and drying) and to monitor time (in days) of pairs of leaves opening. There were no differences between the propagules according to the size for the opening time of leaf pairs, nor for the mortality rate. The increments in diameter and height were larger for the small propagules in the first development periods, but not in the last ones. The large and small propagules did not show significant differences in diameter or height at 154 days. There was high mortality of small propagules due to predation and/or water current carriage, while the mortality for large propagules was higher due to desiccation. The results generally suggest there is no difference in the survival and development of the propagules related to size, as they are more affected by local ecological conditions.

Improving breed‐and‐release programmes in the face of a threatening pathogen, Batrachochytrium dendrobatidis

Abstract As the proportion of threatened species increases, so too does the need for effective conservation strategies. In response, captive breed‐and‐release and habitat mitigation programmes are two conservation actions that are increasing in use and effectiveness. Success of these programmes is frequently hampered by the continued presence of threatening processes. In the case of amphibian reintroductions, a key threatening process that is difficult to eliminate is the deadly fungal pathogen, Batrachochytrium dendrobatidis (Bd). This pathogen is the proximate cause of decline for the threatened green and golden bell frog, Litoria aurea, and has contributed to the failure of previous breed‐and‐release programmes of this amphibian. To investigate whether is it possible to establish a captive‐bred population of L. aurea that could persist in the presence of Bd, a breed‐and‐release programme was conducted in a created habitat that included increased salinity to inhibit fungal growth rates, exclusion of potential reservoir hosts and source animals bred from parents ‘experienced’ with the strain of Bd present in the release environment. The population persisted in the created habitat for more than 4 years (the timescale of monitoring) but suffered higher infection levels compared with nearby extant populations of L. aurea. These infections significantly reduced apparent survival. Infection dynamics were linked to temperature, host density in the previous season, and size and age of the host, and these factors differed from those in extant populations and are likely to have contributed to the high levels of Bd infection at the created site. This article discusses how it may be possible to manipulate these factors to improve the success of future breed‐and‐release programmes, and recommends the construction of warm water bodies and a strategy of prioritizing the release of fewer, large propagules of high body condition and mixed‐age class, over large numbers of younger, smaller animals.

Functional packaging of seeds.

SummaryThe encapsulation of seeds in hard coats and fruit walls (pericarp layers) fulfils protective and dispersal functions in many plant families. In angiosperms, packaging structures possess a remarkable range of different morphologies and functionalities, as illustrated by thermo and hygro‐responsive seed pods and appendages, as well as mechanically strong and water‐impermeable shells. Key to these different functionalities are characteristic structural arrangements and chemical modifications of the underlying sclerenchymatous tissues. Although many ecological aspects of hard seed encapsulation have been well documented, a detailed understanding of the relationship between tissue structure and function only recently started to emerge, especially in the context of environmentally driven fruit opening and seed dispersal (responsive encapsulations) and the outstanding durability of some seed coats and indehiscent fruits (static encapsulations). In this review, we focus on the tissue properties of these two systems, with particular consideration of water interactions, mechanical resistance, and force generation. Common principles, as well as unique adaptations, are discussed in different plant species. Understanding how plants integrate a broad range of functions and properties for seed protection during storage and dispersal plays a central role for seed conservation, population dynamics, and plant‐based material developments.

A non-native agronomic legume (Astragalus cicer L.) alters multiple ecosystem-services in mixed prairie grassland

Cicer milkvetch (Astragalus cicer L.), and other non-native agronomic legumes, are used extensively for forage in North America, but, despite their abundance, few studies have examined their effects when they colonize native grasslands. Cicer milkvetch provides excellent forage for livestock, but given its large size and ability to fix nitrogen, it is likely to affect other ecosystem services provided by grasslands. We have observed cicer milkvetch in the dry mixed-grass prairie of southern Alberta, Canada. The objective of this study was to examine the effects of cicer milkvetch on forage production, carbon storage and plant community diversity after it colonizes native mixed prairie grasslands and further examine whether these effects increase with cicer milkvetch patch size. We compared the ecosystem functions among plots located within a cicer milkvetch patch, beside a patch and 5 m distant from the patch. The plant, as expected has positive effects on forage quantity and quality, reduced plant species diversity and richness, and altered numerous components of the carbon pool, as well as nitrogen availability. Furthermore, larger patches of cicer milkvetch had lower concentrations of soil carbon and nitrogen, and differentially affected other ecosystem properties. Given the potentially large propagule pressure of non-native legumes from agricultural lands, surrounding native grasslands in North America, and our results demonstrating effects on multiple grassland ecosystem services, further consideration and investigation of non-native legumes in grasslands is warranted.

Traits allowing Avicennia marina propagules to overcome seawater salinity

The present study investigated the mechanism by which propagules of Avicennia marina overcome the high surrounding salinity and how they withstand and establish in such a stressful environment. Mature propagules were collected from mother trees at two sites along the Saudi Read Sea shoreline. Based on their sizes, they were divided into small, medium and large propagules. Their morphological characterization and sodium, potassium, chloride and total sugar concentrations (TSC) in embryonic axis, cotyledons and coat were assessed. Toxic ions (Na+ and Cl−) were mainly accumulated in the propagule coat by which they were trapped away from the embryo. The high total sugar accumulation in cotyledons might help in embryonic axis growth. The early development of the embryonic axis inside the propagule before dispersing from the mother plant might help in overcoming high salinity during germination stage and seedling establishment. The large propagules from ‘Al Birk’ site which exhibited the highest TSC and K+/Na+ ratio in cotyledons and well-developed embryonic axis appeared promising for mangrove restoration programs along the Red Sea Shorelines.

Strangers Coming from the Sahara: An Update of the Worldwide Distribution, Potential Impacts and Conservation Opportunities of Alien Aoudad

Biological invasions are considered one of the main causes of the current global biodiversity crisis. Many ungulate species have been introduced worldwide, mainly as game animals or e.g. as an attraction in suburban parks. We compiled the available information on distribution, abundance and ecology of the aoudad Ammotragus lervia outside its native range. We showed that the aoudad has established a number of populations in many countries outside its natural range. Alien nuclei have been recorded in at least 10 countries in Europe, Africa and America but it may be an underestimation. Establishment success differs geographically. North American and Spanish populations are large and still expanding, whereas others are small. This difference might be related to a large propagule pressure, but we suggest it might be due to multiple introduction events or better niche suitability. Information on potential impacts of alien populations on natural systems, human activities and disease spread is still scarce. Despi...

At what scales does aggregated dispersal lead to coexistence?

Aggregation during dispersal can allow persistence of weak competitors, by creating conditions where stronger competitors are more likely to interact with conspecifics than with heterospecifics. However, aggregation mechanisms operate over a wide range of spatial scales, and species experience space in very different ways. The net effect of dispersal aggregation on coexistence will depend on how these scales interact. We show that it is possible to approximate the effects of aggregated dispersal on coexistence by considering three empirically measurable parameters: the spatial scale of interaction (how strongly competition drops off with distance), the spatial scale of aggregation (how large propagule packets are), and the temporal scale of aggregation (how frequently packets arrive). We use a novel metacommunity moment closure based on this approximation and stochastic simulations to show that aggregated dispersal allows for coexistence only when the stronger competitor is both aggregated and interacts at the same or a smaller spatial scale than the weaker competitor. When species interact and are aggregated at the same scales, coexistence outcomes are only weakly sensitive to the absolute scales of interaction and aggregation, as long as the scale of interaction is smaller than the scale of aggregation. However, coexistence is sensitive to the time‐scale of aggregation: increasing the frequency of packet arrival substantially reduces the region of fitness inequalities where both species persist. Finally, coexistence is less likely and global extinction of both competitors is more frequent when aggregation is fixed (with a constant number of propagules per packet), compared to density‐dependent (number of propagules increases with adult density).

Propagule quality mediates invasive plant establishment

Propagule pressure is commonly considered a primary driver of invasive plant establishment and spread. However, the physical size or condition (i.e., quality) of propagules may also affect establishment, particularly under unfavorable habitat conditions such as low light environments. We used an outdoor mesocosm experiment to test the relative contribution of propagule size (number of individuals introduced) and quality (number of rhizome nodes) to the establishment and performance of the highly invasive cogongrass (Imperata cylindrica) under experimental sun and shade treatments. We found that the introduction of higher quality propagules (rhizome segments ≥3 nodes in length) significantly enhanced establishment across both light treatments, and increased final tiller count in the sun treatment. The sun treatment also enhanced rhizome growth, an effect that could increase spread rates and invasion success. Thus, while cogongrass is likely to establish in both sun and shade, introductions of large propagule sizes or large rhizomes in high light environments likely poses the greatest threat to native habitats. Our results demonstrate that propagule quality promoted both establishment and performance of a highly invasive grass species and suggest that propagule quality may play an important but underappreciated role in the invasion process.

Marine invasions enter the genomic era: three lessons from the past, and the way forward.

The expanding scale and increasing rate of marine biological invasions have been documented since the early 20th century. Besides their global ecological and economic impacts, non-indigenous species (NIS) also have attracted much attention as opportunities to explore important eco-evolutionary processes such as rapid adaptation, long-distance dispersal and range expansion, and secondary contacts between divergent evolutionary lineages. In this context, genetic tools have been extensively used in the past 20 years. Three important issues appear to have emerged from such studies. First, the study of NIS has revealed unexpected cryptic diversity in what had previously been assumed homogeneous entities. Second, there has been surprisingly little evidence of strong founder events accompanying marine introductions, a pattern possibly driven by large propagule loads. Third, the evolutionary processes leading to successful invasion have been difficult to ascertain due to faint genetic signals. Here we explore the potential of novel tools associated with high-throughput sequencing (HTS) to address these still pressing issues. Dramatic increase in the number of loci accessible via HTS has the potential to radically increase the power of analyses aimed at species delineation, exploring the population genomic consequences of range expansions, and examining evolutionary processes such as admixture, introgression, and adaptation. Nevertheless, the value of this new wealth of genomic data will ultimately depend on the ability to couple it with expanded “traditional” efforts, including exhaustive sampling of marine populations over large geographic scales, integrated taxonomic analyses, and population level exploration of quantitative trait differentiation through common-garden and other laboratory experiments.

Patterns of plant invasions at small spatial scale correspond with that at the whole country scale

Invasions were studied at different spatial scales, however these scales were rarely compared. The aim of this study is to compare the rate of expansion of eight alien plant species within the borders of the city with expansion in the whole country and to analyse changes in distribution of these plant species in the last 30 years. We hypothesised that at the scale of the city, despite of stronger human impact, invasion processes will perform in a similar way as at the scale of whole country. Distribution changes of Bidens frondosa, Conyza canadensis, Echinocystis lobata, Helianthus tuberosus, Impatiens parviflora, Reynoutria japonica, Solidago canadensis and S. gigantea in 1 km squares grid was examined in the Warta River Valley in Poznań (W Poland) in 2013 and compared to data collected during 1980–1984. All species increased their distribution within the study area. E. lobata had the highest increment of occupied grid squares (from 0 in 1980’s to 28 in 2013), and S. gigantea had the lowest (from 8 to 9). Echinocystis lobata reached the highest invasion success, which results from species traits (hydrochory) and large propagule pressure from garden plots. Between species with different ecological traits residence time has relatively little influence on invasion success, however in cases of species with similar traits (S. canadensis and S. gigantea) residence time is a crucial factor determining invasion success. Although urban ecosystems are more vulnerable to biological invasions, this process occurs in a similar way as in the whole country. This similarity is connected with similar factors responsible for spread of invasive species: propagule pressure, time since introduction and spatial distributions of invasible habitats.

Propagule size and shape may promote local wind dispersal in freshwater zooplankton-a wind tunnel experiment

Current evidence supports that dormant eggs of many zooplankton species from inland waters can be transported by wind. However, little is known about variation in wind dispersal propensity among different species and propagule types. Here, we experimentally investigate the wind speed required to pick-up propagules of a wide range of freshwater zooplankton species on different substrates. Counter-intuitively, larger propagules were consistently picked-up at lower wind speeds than smaller propagules. Grain size of the substrate affected adhesion because propagules were more easily picked-up from fine grained than from coarse grained or smooth surfaces. Overall, these results suggest that propagule morphology affects wind dispersal propensity and propagule bank erosion, providing a possible explanation for the large interspecific and intraspecific variation in propagule size and shape observed in nature. Ultimately, a better understanding of the link between propagule morphology, habitat structure, and dispersal propensity will be useful to understand diversity patterns and temporal dynamics in lentic aquatic habitats. It could also help to predict range expansion of freshwater zooplankton species, many of which are invasive outside of their natural ranges.

Determinants of successful establishment and post‐translocation dispersal of a new population of the critically endangered St. Croix ground lizard (Ameiva polops)

Translocation to areas free of exotic predators, habitat degradation, or disease may be the most viable restoration option for many endangered species. We report on a successful translocation of the critically endangered St. Croix ground lizard, Ameiva polops, extirpated from St. Croix, U.S. Virgin Islands, Caribbean, by predation from introduced mongooses (Herpestes auropunctatus). We translocated 57 adult A. polops from Green Cay to Buck Island in May 2008. We placed 4 females and 3 males each in eight, 100 m2, enclosures on Buck Island for 71 days, then the enclosures were opened. During the enclosure period, 20 individuals were identified and 32 others were seen. The average number sighted per survey was only 5.28 (range = 2–10). One hatchling was sighted in an enclosure, indicating a translocated female successfully nested. Body condition of the translocated individuals increased significantly by the end of the enclosure period. Population monitoring surveys at 61 sites across Buck Island showed that 5 years after the initial translocation in June 2013, the new population had grown to an estimated 1,473 individuals and occupied 58.9% of the island. We attribute eradication of mongoose, life history of the species, large propagule size, condition of habitat, soft‐release, use of adults, interagency collaboration, and systematic assessment as primary factors that facilitated this successful translocation. Our findings provide meaningful insights on factors that enhance the potential for successful translocations, and point to new strategies aimed at restoring populations of endangered reptiles in their native ranges.

Long-term colonization ecology of forest-dwelling species in a fragmented rural landscape - dispersal versus establishment.

Species colonization in a new habitat patch is an efficiency indicator of biodiversity conservation. Colonization is a two-step process of dispersal and establishment, characterized by the compatibility of plant traits with landscape structure and habitat conditions. Therefore, ecological trait profiling of specialist species is initially required to estimate the relative importance of colonization filters. Old planted parks best satisfy the criteria of a newly created and structurally matured habitat for forest-dwelling plant species. We sampled species in 230 ancient deciduous forests (source habitat), 74 closed-canopy manor parks (target habitats), 151 linear wooded habitats (landscape corridors), and 97 open habitats (isolating matrix) in Estonia. We defined two species groups of interest: forest (107 species) and corridor specialists (53 species). An extra group of open habitat specialists was extracted for trait scaling. Differing from expectations, forest specialists have high plasticity in reproduction mechanisms: smaller seeds, larger dispersules, complementary selfing ability, and diversity of dispersal vectors. Forest specialists are shorter, less nutrient-demanding and mycorrhizal-dependent, stress-tolerant disturbance-sensitive competitors, while corridor specialists are large-seeded disturbance-tolerant competitors. About 40% of species from local species pools have immigrated into parks. The historic forest area, establishment-related traits, and stand quality enhance the colonization of forest specialists. The openness of landscape and mowing in the park facilitate corridor specialists. Species traits in parks vary between a forest and corridor specialist, except for earlier flowering and larger propagules. Forest species are not dispersal limited, but they continue to be limited by habitat properties even in the long term. Therefore, the shady parts of historic parks should be appreciated as important forest biodiversity-enhancing landscape structures. The habitat quality of secondary stands can be improved by nurturing a heterogeneous shrub and tree layer, and modest herb layer management.

Factors Influencing the Abundance of Pests in Production Fields and Rates of Interception of <I>Dracaena marginata</I> Imported From Costa Rica

Importation of live nursery plants, like Dracaena marginata Lamoureux (Ruscaceae), can provide a significant pathway for the entry of foliar pests from overseas into the United States. We studied the abundance of foliar pests of quarantine importance found on Costa Rican-grown D. marginata. These include five genera of leafhoppers (Heteroptera: Cicadellidae, Oncometopia, Caldweliola, Diestostema, Cypona, and Empoasca), Florida red scale (Heteroptera: Disapididae, Chrysomphalus aoinidum (L.)), katydids (Orthoptera: Tettigoniidae), and a snail (Succinea costarricana von Martens (Gastropoda, Stylommatophora, Succineidae)). In our first study, we examined the rationale behind size restrictions on Dracaena cuttings imported into the United States from Costa Rica. When comparing plant size, no differences were found in the abundance of quarantined pests on small (15-46 cm), medium (46-81 cm), and large (81-152 cm) propagules. In a second study, we estimated monthly abundances of pests in production plots for 1 yr to determine their relationship to rates of interception at U.S. ports. In any given month, < 6% of the marketable shoots standing in the field were infested with at least one quarantine pest. There was no relationship between the average monthly frequencies of pest detection in the field and in U.S. inspection ports. Pest detections increased during the 1 mo when average monthly shipments were abnormally high. Our data suggest that off-shore postprocessing efforts to remove pest-infested material from the market stream need to be adjusted to accommodate sharp increases in the volume of shipped plants.

The interacting effects of diversity and propagule pressure on early colonization and population size

We are now beginning to understand the role of intraspecific diversity on fundamental ecological phenomena. There exists a paucity of knowledge, however, regarding how intraspecific, or genetic diversity, may covary with other important factors such as propagule pressure. A combination of theoretical modelling and experimentation was used to explore the way propagule pressure and genetic richness may interact. We compare colonization rates of the Australian bivalve Saccostrea glomerata (Gould 1885). We cross propagule size and genetic richness in a factorial design in order to examine the generalities of our theoretical model. Modelling showed that diversity and propagule pressure should generally interact synergistically when positive feedbacks occur (e.g. aggregation). The strength of genotype effects depended on propagule size, or the numerical abundance of arriving individuals. When propagule size was very small (<4 individuals), however, greater genetic richness unexpectedly reduced colonization. The probability of S. glomerata colonization was 76% in genetically rich, larger propagules, almost 39 percentage points higher than in genetically poor propagules of similar size. This pattern was not observed in less dense, smaller propagules. We predict that density-dependent interactions between larvae in the water column may explain this pattern.