How important is long‐distance seed dispersal for the regional survival of plant species?

Long‐distance seed dispersal is generally assumed to be important for the regional survival of plant species. In this study, we quantified the importance of long‐distance seed dispersal for regional survival of plant species using wind dispersal as an example. We did this using a new approach, by first relating plant species’ dispersal traits to seed dispersal kernels and then relating the kernels to regional survival of the species. We used a recently developed and tested mechanistic seed dispersal model to calculate dispersal kernels from dispersal traits. We used data on 190 plant species and calculated their regional survival in two ways, using species distribution data from 36,800 1 km²‐grid cells and 10,754 small plots covering the Netherlands during the largest part of the 20th century. We carried out correlation and stepwise multiple regression analyses to quantify the importance of long‐distance dispersal, expressed as the 99‐percentile dispersal distance of the dispersal kernels, relative to the importance of median‐distance dispersal and other plant traits that are likely to contribute to the explanation of regional survival: plant longevity (annual, biennial, perennial), seed longevity, and plant nutrient requirement. Results show that long‐distance dispersal plays a role in determining regional survival, and is more important than median‐distance dispersal and plant longevity. However, long‐distance dispersal by wind explains only 1–3% of the variation in regional survival between species and is equally important as seed longevity and much less important than nutrient requirement. In changing landscapes such as in the Netherlands, where large‐scale eutrophication and habitat destruction took place in the 20th century, plant traits indicating ability to grow under the changed, increasingly nutrient‐rich conditions turn out to be much more important for regional survival than seed dispersal.     

Shorebirds as important vectors for plant dispersal in Europe

Shorebirds (Charadriiformes) undergo rapid migrations with potential for long‐distance dispersal (LDD) of plants. We studied the frequency of endozoochory by shorebirds in different parts of Europe covering a broad latitudinal range and different seasons. We assessed whether plants dispersed conformed to morphological dispersal syndromes. A total of 409 excreta samples (271 faeces and 138 pellets) were collected from redshank Tringa totanus, black‐winged stilt Himantopus himantopus, pied avocet Recurvirostra avosetta, northern lapwing Vanellus vanellus, Eurasian curlew Numenius arquata and black‐tailed godwit Limosa limosa in south‐west Spain, north‐west England, southern Ireland and Iceland in 2005 and 2016, and intact seeds were extracted and identified. Godwits were sampled just before or after migratory movements between England and Iceland. The germinability of seeds was tested. Intact diaspores were recovered from all bird species and study areas, and were present in 13% of samples overall. Thirteen plant families were represented, including Charophyceae and 26 angiosperm taxa. Only four species had an ‘endozoochory syndrome’. Four alien species were recorded. Ellenberg values classified three species as aquatic and 20 as terrestrial. Overall, 89% of seeds were from terrestrial plants, and 11% from aquatic plants. Average seed length was higher in redshank pellets than in their faeces. Six species were germinated, none of which had an endozoochory syndrome. Seeds were recorded during spring and autumn migration. Plant species recorded have broad latitudinal ranges consistent with LDD via shorebirds. Crucially, morphological syndromes do not adequately predict LDD potential, and more empirical work is required to identify which plants are dispersed by shorebirds. Incorporating endozoochory by shorebirds and other migratory waterbirds into plant distribution models would allow us to better understand the natural processes that facilitated colonization of oceanic islands, or to improve predictions of how plants will respond to climate change, or how alien species spread.     

Widespread Indo-Pacific Shore-fish Species: A Challenge for Taxonomists, Biogeographers, Ecologists, and Fishery and Conservation Managers

Many shore-fish species are currently considered to have wide distributions; for example, perhaps as many as half of all Indo-Pacific reef-fish species have distributions that span or even extend beyond the Indo-West Pacific. However, wide distributions of some and perhaps many species may be an artefact, reflecting taxonomic practice and understanding. The reappraisal of widespread species represents a daunting task for taxonomists, particularly given the current trend of ever-reducing support for systematic ichthyology. Our poor understanding of widespread shore-fish species has serious implications for cladistic biogeographers, ecologists, fishery and conservation managers.     

The mismatch in distributions of vertebrates and the plants that they disperse

Little is known about how mutualistic interactions affect the distribution of species richness on broad geographic scales. Because mutualism positively affects the fitness of all species involved in the interaction, one hypothesis is that the richness of species involved should be positively correlated across their range, especially for obligate relationships. Alternatively, if mutualisms involve multiple mutualistic partners, the distribution of mutualists should not necessarily be related, and patterns in species distributions might be more strongly correlated with environmental factors. In this study, we compared the distributions of plants and vertebrate animals involved in seed‐dispersal mutualisms across the United States and Canada. We compiled geographic distributions of plants dispersed by frugivores and scatter‐hoarding animals, and compared their distribution of richness to the distribution in disperser richness. We found that the distribution of animal dispersers shows a negative relationship to the distribution of the plants that they disperse, and this is true whether the plants dispersed by frugivores or scatter‐hoarders are considered separately or combined. In fact, the mismatch in species richness between plants and the animals that disperse their seeds is dramatic, with plants species richness greatest in the in the eastern United States and the animal species richness greatest in the southwest United States. Environmental factors were corelated with the difference in the distribution of plants and their animal mutualists and likely are more important in the distribution of both plants and animals. This study is the first to describe the broad‐scale distribution of seed‐dispersing vertebrates and compare the distributions to the plants they disperse. With these data, we can now identify locations that warrant further study to understand the factors that influence the distribution of the plants and animals involved in these mutualisms.     

Spatial and environmental effects on a rock‐pool metacommunity depend on landscape setting and dispersal mode

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Life history influences the vulnerability of New Zealand galaxiids to invasive salmonids

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Evidence that Kenyan House Sparrows Passer domesticus invaded from multiple sites

Here we characterize genetic patterns across the range of House Sparrows in Kenya using six microsatellite markers. We screened House Sparrows from two remote locations in northern Kenya, Marsabit (n = 24) and Wajir (n = 27), which are separated from other colonized areas in Kenya by minimally developed, arid habitat, and then compared these birds with House Sparrows in 10 more central and longer established Kenyan cities (n = 233) in this range. House Sparrows from Marsabit and Wajir originated from a separate source, probably Somalia and/or Ethiopia, from other Kenyan House Sparrows, probably Mombasa. Furthermore, the genetic characteristics of northern and southern populations indicate that they have not yet mixed, supporting a hypothesis that the large, minimally (human) developed, arid landscape spanning nearly all of northern Kenya, including the 100 000 km² Chalbi Desert, is a barrier to dispersal for House Sparrows.     

Riverine networks constrain β‐diversity patterns among fish assemblages in a large Neotropical river

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Non-native freshwater fishes in Norway: history, consequences and perspectives

At present, there are 43 self-sustaining fish species in Norwegian fresh waters, 11 (26%) of which are non-native, representing four families (Salmonidae, Cyprinidae, Centrarchidae and Ictaluridae). Human-mediated fish introductions probably began in the 15th century with common carp Cyprinus carpio, but most have occurred between the late 1800s and late 1900s. The number of known established populations varies from one (goldfish Carassius auratus ) to nearly 250 (tench Tinca tinca ). Dispersal risk is also highest with tench, which is being spread by anglers for its appeal as a trophy fish. Intentional introductions to improve amenity angling have been part of fisheries management programmes ( e.g. brook trout Salvelinus fontinalis ), so this appears to be an increasingly common introduction vector despite the prohibition under legislation of introducing any species of non-native fishes. Some introduced species, such as brook trout, have declined in abundance and number of populations as the quality of acidified waters has been restored, being replaced by native brown trout Salmo trutta . Further range expansion by some species ( e.g. common carp, goldfish and pumpkinseed Lepomis gibbosus ) is probably restricted by current climatic conditions.     

Predicting potential impacts of environmental flows on weedy riparian vegetation of the Hawkesbury–Nepean River,south‐eastern Australia

Remnants of native riparian vegetation on the floodplain of the Hawkesbury–Nepean River near Sydney, have significant conservation value, but contain a large component of weeds (i.e. exotic species that have become naturalized). A proposal for the introduction of environmental flows required an assessment of potential impacts on 242 native and 128 exotic species recorded along 215 km of the river. The likely effects of frequency, season, depth and duration of inundation were considered in relation to habitat, dispersal season and tolerance to waterlogging. Overseas studies provided only limited information applicable to the study area; however, comparisons with similarly highly modified riparian habitats in New Zealand were instructive. Depth and season of inundation appear to be the variables with the greatest potential for differential effects on weeds and native plants. Because of likely spread of propagules and enhancement of growth under the present nutrient‐enriched conditions, environmental flows that would cause more frequent flooding to higher levels of the riparian zone were judged to be of more benefit to weed species than native species, unless supported by bushland management including weeding. Predictions were limited by incomplete data on Hawkesbury–Nepean species, but two types of environmental flow were judged to be potentially beneficial for native water‐edge plants, and worth testing and monitoring: first, flows that maintain continuous low‐level flow in the river, and second, higher level environmental flows restricted to the river‐edge habitat in autumn (the season in which a greater proportion of native species than weed species are known to disperse propagules). In summary, the presence of environmental weeds in riparian vegetation constrain the potential for environmental flows to improve river health. However, with ongoing monitoring, careful choice of water level and season of flow may lead to environmental flows that add to our knowledge, and benefit riparian vegetation along with other river system components.     

Seed Dispersal by Avian Frugivores: Non‐random Heterogeneity at Fine Scales

Seed dispersal studies have primarily examined dispersal as a function of distance from the parent tree and/or heterogeneity in dispersal due to animal use of nesting, roosting and sleeping sites. However, non‐random heterogeneity in seed dispersal is also likely to result from the post‐foraging behavior and movement of frugivores which prefer certain trees. To characterize variation in seed rain at fine scales, we studied the dispersal curve of Prunus ceylanica, a primarily bird‐dispersed species. We compared seed rain at conspecifics, heterospecific fruiting trees with similar frugivore assemblages, emergent trees, and the landscape surrounding these trees. Seed rain of P. ceylanica was found to peak globally under the canopy of conspecifics but to peak locally under the canopy and immediate neighborhood of heterospecific fruiting trees. Our results demonstrate that seed rain is highly clumped even at fine spatial scales. A large proportion of seeds are dispersed in specific, localized regions. This variation can have important implications for plant population dynamics and might significantly alter the impact of post‐dispersal processes. Seed dispersal models may need to incorporate this heterogeneity to explain manifestations of spatially explicit dynamics like mixed species ‘orchards’.     

Raptors as legitimate secondary dispersers of weed seeds

Although raptors are not usually seen as seed dispersers, we demonstrate their important ecological role as legitimate seed dispersers of weeds. On the oceanic island of Fuerteventura in the Canary Islands, up to 11 000 weed seeds from a total of 39 and 62 different plant species, respectively, were found in 300 and 319 pellets, respectively, of two native predatory birds, the Common Buzzard Buteo buteo and the Eurasian Kestrel Falco tinnunculus, which consumed European Rabbits Oryctolagus cuniculus and Barbary Ground Squirrels Atlantoxerus getulus, both invasive mammals that carried these seeds in their guts. Four and seven weed species appeared with a frequency of occurrence greater than 10% in the pellets of Kestrels and Buzzards, respectively. Despite the time interval between pellet collection and germination experiments, almost 10% of planted seeds germinated, even after passing through two digestive processes, one inside the mammal and another inside the raptor. Our study encourages a change of perspective in this regard, as raptors may be involved in complex interactive dispersal processes on a wider geographical scale.     

Revegetation of an artificial cut-slope by seeds dispersed from the surrounding vegetation

We examined a method for revegetation of cut-slopes in Tochigi, Japan, using only natural plant dispersal from the surrounding vegetation. We examined plant establishment in six plots in a cut-slope in bedrock (inclination: 65°, direction: S45°W) treated with various types of netting and fertilizer. We surveyed the plant communities, individual trees, and seed rain on the cut-slope, as well as the plant community on the undisturbed upper slope. Revegetation method using polyethylene netting with fertilizer and water-retention material was the most effective. The resulting plant community was dominated by Pinus densiflora, with a cover of 49.0±11.4% after 5 years. This plant community consisted of 19 species, including ten tree species and a density of 26.2 trees/m². Revegetation method using palm-fiber netting with fertilizer also resulted in high plant cover after five years, although little revegetation grew on this plot in the earlier years. The roughness of the palm fiber may have inhibited revegetation. Application of fertilizer was essential for the success of this natural revegetation method. In addition, the revegetated plant community was strongly influenced by seed rain from the vegetation of the upper slope. The number of trees that became established was much lower than the number of tree seeds that were dispersed, possibly because of the absence of soil. We recommend that soil is allowed to accumulate or that a base of material to facilitate plant growth is added. Successful revegetation was achieved even under the harsh conditions of this cut-slope.     

The invasion of Argentina by the European wild rabbit Oryctolagus cuniculus

• 1 We provide an updated distribution and dispersal rate of the introduced European rabbit Oryctolagus cuniculus in Argentina.
• 2 According to our results this invasive species is currently colonizing parts of Mendoza and Neuquén Provinces, where rivers are very important in the spread of the rabbits, especially in unfavourable areas. The maximun rate of dispersal registered in this study was 9 km/year.
• 3 Some information was obtained to indicate that the presence of this exotic species threatens agriculture, livestock, forestry, and natural ecosystems of the Patagonia region.

     

Movement and dispersal of the invasive signal crayfish Pacifastacus leniusculus in upland rivers

1. The American signal crayfish Pacifastacus leniusculus, an invasive species widely introduced throughout Europe, is a major threat to native European crayfish species and is causing increasing concern because of its wide impact on aquatic ecosystems. 2. Whilst various control and management methods have been proposed, very little is known about the factors influencing dispersal and movements of signal crayfish. 3. Sixty‐four adult signal crayfish (carapace length 31.9–63.8 mm) were radiotagged in upland rivers in northern England, during four periods. Tracking was carried out at two sites, a low‐density establishing population and a high‐density established population. Tracking was carried out at both sites concurrently during midsummer (June to August 2002), during late summer (August to September 2001) at the low‐density population site and during autumn to winter (October to February 2000/01) at the high‐density population site. 4. Maximum movement occurred during midsummer. Temperature appeared to be a major factor influencing the timing and extent of movements between tracking periods. 5. The frequency distribution of the maximum distance moved upstream and downstream by radiotagged crayfish showed an inverse power relationship. The median maximal upstream and downstream distances moved were 13.5 m (range 0–283 m) and 15 m (range 0–417 m), respectively. There was a significant difference between the distributions of upstream and downstream ranges, with greater distances moved downstream. 6. All downstream movements made by crayfish appeared to be active movements and not the result of passive movement during periods of high discharge. There was no apparent influence of size, sex or density on the amount of movement recorded. 7. The study provides important information on the spatial and temporal behaviour of introduced crayfish in upland lotic systems. In contrast to lowland rivers, our results suggest that flow or gradient may influence the invasive potential of signal crayfish in an upstream direction in upland rivers.     

Distribution and range expansion of deer in Ireland

• 1 Throughout Europe, the range of many deer species is expanding. We provide current distribution maps for red deer Cervus elaphus, sika Cervus nippon, fallow deer Dama dama and muntjac deer Muntiacus sp. in Ireland, and estimates of range expansion rates for red deer, sika and fallow deer.
• 2 There was a considerable expansion in the ranges of red deer, sika and fallow deer between 1978 and 2008. The compound annual rate of expansion was 7% for red deer, 5% for sika and 3% for fallow deer. The total range increase was 565% for red deer, 353% for sika and 174% for fallow deer. The potential implications of these expansions are discussed.
• 3 There are unknown numbers of red‐sika hybrid deer in some parts of Ireland. Range expansion is likely to lead to further hybridizations with implications for the genetic integrity of deer stocks.
• 4 Sightings of free‐roaming muntjac deer were first recorded in 2007. The distribution of confirmed sightings of single and multiple animals in the eastern region of Ireland suggests multiple releases.
• 5 Deer are already impacting on both the economic and biodiversity values of habitats in Ireland, where, at present, no sustainable deer management policy exists.

     

Incursion and excursion of Antarctic biota: past, present and future

Aim To investigate the major paradigms of intense isolation and little anthropogenic influence around Antarctica and to examine the timings and scales of the modification of the southern polar biota. Location Antarctica and surrounding regions. Methods First, mechanisms of and evidence for long‐term isolation are reviewed. These include continental drift, the development of a surrounding deep‐water channel and the Antarctic Circumpolar Current (ACC). They also include levels of endemism, richness and distinctiveness of assemblages. Secondly, evidence for past and modern opportunities for species transport are investigated. Comparative levels of alien establishments are also examined around the Southern Ocean. Discussion On a Cenozoic time‐scale, it is clear that Gondwana's fragmentation led to increasing geographical isolation of Antarctica and the initiation of the ACC, which restricted biota exchange to low levels while still permitting some movement of biota. On a shorter Quaternary time‐scale, the continental ice‐sheet, influenced by solar (Milankovitch) cycles, has expanded and contracted periodically, covering and exposing terrestrial and continental shelf habitats. There were probably refugia for organisms during each glacial maxima. It is also likely that new taxa were introduced into Antarctica during cycles of ice sheet and oceanic front movement. The current situation (a glacial minimum) is not ‘normal’; full interglacials represent only 10% of the last 430 ka. On short (ecological) time‐scales, many natural dispersal processes (airborne, oceanic eddy, rafting and hitch‐hiking on migrants) enable the passage of biota to and from Antarctica. In recent years, humans have become influential both directly by transporting organisms and indirectly by increasing survival and establishment prospects via climate change. Main conclusions Patterns of endemism and alien establishment are very different across taxa, land and sea, and north vs. south of the Polar Frontal Zone. Establishment conditions, as much as transport, are important in limiting alien establishment. Three time‐scales emerge as important in the modification of Antarctica's biota. The natural ‘interglacial’ process of reinvasion of Antarctica is being influenced strongly by humans.     

Metacommunity organisation,spatial extent and dispersal in aquatic systems: patterns,processes and prospects

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