Dispersal Ecology

Current fossil, genetic, and archeological data indicate that Homo sapiens originated in Africa in the late Middle Pleistocene. By the end of the Late Pleistocene, our species was distributed across every continent except Antarctica, setting the foundations for the subsequent demographic and cultural changes of the Holocene. The intervening processes remain intensely debated and a key theme in hominin evolutionary studies. We review archeological, fossil, environmental, and genetic data to evaluate the current state of knowledge on the dispersal of Homo sapiens out of Africa. The emerging picture of the dispersal process suggests dynamic behavioral variability, complex interactions between populations, and an intricate genetic and cultural legacy. This evolutionary and historical complexity challenges simple narratives and suggests that hybrid models and the testing of explicit hypotheses are required to understand the expansion of Homo sapiens into Eurasia.

Landscape configuration and dispersal characteristics are major determinants of population distribution and persistence in fragmented habitat. An individual-based spatially explicit population model was developed to investigate these factors using the distribution of nuthatches in an area of eastern England as an example. The effects of immigration and increasing the area of breeding quality habitat were explored. Predictions were compared with observed population sizes in the study area. Our model combined a nuthatch population simulator based on individual behaviour with a grid-based representation of the landscape; nuthatch life cycle and immigration parameters were user selectable. A novel aspect of the model is user-selection of habitat perceptual range. Using a realistic set of parameters, the number of breeding pairs predicted by the model matched observed numbers. According to model simulations, the main cause of nuthatch scarcity in the study area was the inability of patches to support viable populations without immigration from elsewhere. Modelled habitat management, which increased breeding quality habitat in existing woods, lowered the threshold above which the study area population became self-sustaining. The existence of a large core habitat area was critical in producing a self-sustaining population in this landscape, the same area in dispersed small woods failed to sustain populations.

We reviewed follow-up studies from Finnish and Swedish streams that have been restored after timber floating to assess the abiotic and biotic responses to restoration. More specifically, from a review of 18 case studies (16 published and 2 unpublished), we determined whether different taxonomic groups react differently or require different periods of time to respond to the same type of restoration. Restoration entailed returning coarse sediment (cobbles and boulders) and sometimes large wood to previously channelized turbulent reaches, primarily with the objective of meeting habitat requirements of naturally reproducing salmonid fish. The restored streams showed a consistent increase in channel complexity and retention capacity, but the biotic responses were weak or absent in most species groups. Aquatic mosses growing on boulders were drastically reduced shortly
after restoration, but in most studies, they recovered after a few years. Riparian plants, macroinvertebrates and fish did not
show any consistent trends in response. We discuss seven alternative explanations to these inconsistent results and conclude that two decades is probably too short a time for most organisms to recover. We recommend long-term monitoring using standardized methods, a landscape-scale perspective and a wider range of organisms to improve the basis for judging to what extent restoration in boreal streams has achieved its goal of reducing the impacts from timber floating.

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 southwest Spain, northwest 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.

A thin, white coloured ash/pumice layer on top of the poor macrofossil units at the Selárgil locality yields a rich late Messinian palynoflora that was deposited under a markedly different taphonomic setting than most other late Cainozoic floras discussed in this book. Pollen contained in this volcanic sediment apparently was deposited in a very short time during the actual ash fall, whereas in most other Cainozoic formations in Iceland pollen was deposited in clastic sediments over a longer time interval. The unusual taphonomy of the Selárgil pollen and spores assemblage possibly acted as filter against insect pollinated woody species such as Rhododendron subsect. Pontica and other tree taxa that would otherwise be expected (Juglandaceae, Ulmaceae). Overall, the arboreal flora at Selárgil contains a number of partly warmth-loving relict taxa from older formations (Cathaya, Scyadopitys, Tetracentron) and some newcomers (Quercus, two types of Ericaceae). The occurrence of a new type of Quercus with clear biogeographic affinities to North America points to a functioning land bridge between Iceland and Greenland during the Late Miocene and to climatic conditions in northern North America and Greenland that would have allowed for migration of oaks to Iceland.

Fruit-eating bats play a fundamental role in animal seed dispersal and should be considered key actors in tropical forest restoration. We explored the use of commercial fruits as attractants for bats to increase seed dispersal to areas affected by forest fires in southern Mexico. We captured bats and collected seeds from feces and seed rain at perturbed sample sites where mature bananas and mangos were placed, and from non-treated control sites. Bat and bat-dispersed plant species richness and abundance were analyzed, and the importance of each bat species as a disperser was evaluated. Additionally, germination boxes were set up to evaluate the germination of seeds found in bat feces. We captured 724 individuals of 16 frugivorous bat species, 15 spp in treated
and 12 spp in control sites. Sowell’s Short-tailed bat, Toltec Fruit-eating bat and the Western Long-tongued bat showed higher abundances in treated sites, suggesting that these three species were attracted by fruits. The most important disperser was the Sowell’s Short-tailed bat, followed by the Jamaican Fruit-eating and Toltec Fruit-eating bat. A greater proportion of pioneer species and trees, followed by shrubs, were found in the overall bat diet. The germination percentage was > 50%, suggesting that the use of fruits to attract bats can be a feasible wildlife management activity to encourage the succession process. We recommend further studies to test and improve this activity.

Dispersal distances of 17 species of butterflies in tropical Singapore were signifi- cantly greater in forest than in urban habitat. Butterflies in urban plots frequently moved within suitable habitat (park/grassland) patches but rarely crossed non-habi- tat patches suggesting potential isolation and a need for urban corridors.

Availability and dispersal of target plant propagules and applied management techniques can considerably affect the success of grassland restoration. In our study we explored the effect of sheep grazing on plant species composition of an early staged recovering grassland, which developed on newly created soil surfaces. We recorded the presence and cover of vascular plant species in 17 grazed and 6 ungrazed plots during three consecutive years after the restoration of a landfill in southern Italy. A DCA ordination based on species percentage cover was calculated to assess the species composition of the plots in the three years. Plant assemblages were compared to adjacent reference grassland in terms of species composition and cover of functional groups based on their role (i.e. target species or weeds) and their seed dispersal potential (i.e. high or low epizoochorous ranking index). For each parameter, Relative Response Indices (RRIs) were calculated to assess the relationship between the vegetation characteristics of the restored areas and the reference grassland. The DCA ordination of plant communities in the restored area revealed gradients of increasing similarity to reference grassland as a function of successional age and grazing. For most of the considered vegetation characteristics, RRIs in restored grassland became more similar to the reference grassland with increasing successional age and under grazed conditions. Besides underlining the role of passive restoration in supporting effective grassland recovery, our results revealed that extensive sheep grazing even from the early successional stages can improve target species dispersal and establishment, and enhance grassland restoration. Our results suggest that grazing can improve the feasibility and sustainability of restoration projects by saving costs of fence installation and providing forage for local animal husbandry.

Entomopathogenic nematodes (EPNs) are insect parasites used as biological control agents. Free-living infective juveniles (IJs) of EPNs employ host-seeking behaviors to locate suitable hosts for infection. We found that EPNs can differentiate between naïve and infected hosts, and that host attractiveness changes over time in a species-specific manner. We used solid-phase microextraction and gas chromatography/mass spectrometry to identify volatile chemical cues that may relay information about a potential host's infection status and resource availability. Among the chemicals identified from the headspace of infected hosts, 3-Methyl-2-buten-1-ol (prenol) and 3-Hydroxy-2-butanone (AMC) were selected for further behavioral assays due to their temporal correlation with the behavioral changes of IJs towards the infected hosts. Both compounds were repulsive to IJs of Steinernema glaseri and S. riobrave in a dose-dependent manner when applied on an agar substrate. Furthermore, the repulsive effects of prenol were maintained when co-presented with the uninfected host odors, overriding attraction to uninfected hosts. Prenol was attractive to dauers of some free-living nematodes and insect larvae. These data suggest that host-associated chemical cues may have several implications in EPN biology, not only as signals for avoidance and dispersal of conspecifics, but also as attractants for new potential hosts. Entomopathogenic nematodes (EPNs) are insect-killing parasites used in biological control and are a model system for studying host-parasite interactions. EPNs can infect and kill a host within 48 hours and are commercially available for use in home gardens and industrial agriculture 1, 2. In the EPN life cycle, free-living infective-juveniles (IJs) encounter a host (either uninfected or possibly at an early stage of infection) (Fig. 1A), and then decide whether or not to invade the host. Once an IJ invades a host it releases symbiotic bacteria (Fig. 1B), which proliferate and help to both kill the host and provide a food source for the growing nematodes 3 (Fig. 1C). Steinernema spp. are gonochoristic, requiring a male and female in order to produce offspring 4. Within the host approximately 2–3 generations of nematodes can be produced (Fig. 1D), but eventually resources begin to run out inside the insect cadaver 2. As resources are depleted, the L2 juveniles will associate once more with the bacteria and take an alternative developmental pathway, becoming infective juveniles (IJs) rather than L3 juveniles. These IJs will then emerge and search for a new host to infect 2, 5 (Fig. 1E). In their search for a new host there are two host-seeking strategies–employed by IJs–which represent endpoints of a continuous spectrum. The first is a cruise foraging strategy where the IJ spends the majority of its time actively moving in search of a host 6, 7. The second strategy is an ambush foraging strategy where the IJ employs a sit-and-wait approach, waiting for a potential host to pass close by, allowing the IJ to attach and invade 7, 8. Between these two endpoint foraging strategies there are species of EPNs that have been classified as intermediates 6, 9. These foraging strategies are employed by individuals within a population and it has been shown that even for a species like S. carpocapsae. which is described as an ambush forager, a small proportion of individuals are cruise foragers and have been referred to as " sprinters " 8. Here, we worked with four species of Steinernema: S. carpocapsae, an ambush forager 6, 8 ; S. glaseri, a cruise forager 6, 9 ; and S. riobrave and S. feltiae, which are described as intermediate foragers 6, 9. EPN foraging strategies and the decision of whether or not to infect certain hosts is informed by olfactory and mechanosensory cues. Previous work has shown that volatile odorants emitted by uninfected insects elicit host-seeking behavior in EPN IJs 10–12. IJs rely on chemical cues in the environment to locate, identify, and evaluate their hosts 7. It has been shown that EPNs can distinguish between uninfected and infected hosts, and even Published: xx xx xxxx OPEN

Dispersal can strongly influence the demographic and evolutionary trajectory of populations. For many species, little is known about dispersal, despite its importance to conservation. The Greater Sage-Grouse (Centrocercus urophasianus) is a species of conservation concern that ranges across 11 western U.S. states and 2 Canadian provinces. To investigate dispersal patterns among spring breeding congregations, we examined a 21-locus microsatellite DNA dataset of 3,244 Greater Sage-Grouse sampled from 763 leks throughout Idaho, Montana, North Dakota, and South Dakota, USA, across 7 yr. We recaptured ~2% of individuals, documenting 41 instances of breeding dispersal, with 7 dispersal events of 50 km, including 1 of 194 km. We identified 39 recaptures on the same lek up to 5 yr apart, which supports the long-held paradigm of philopatry in lekking species. We found no difference between the sexes in breeding dispersal distances or in the tendency to disperse vs. remain philopatric. We also documented movements within and among state-delineated priority areas of conservation importance, further supporting the need to identify movement corridors among these reserves. Our results can be used to better inform the assumptions of count-based population models and the dispersal thresholds used to model population connectivity.