72 Matching Annotations
  1. Sep 2021
    1. J. Vizentin-Bugoni, P. K. Maruyama, C. S. de Souza, F. Ollerton, A. R. Rech, M. Sazima, “Plant-pollinator networks in the tropics: A review,” in Ecological Networks in the Tropics, W. Dáttilo, V. Rico-Gray, Eds. (Springer, 2018), pp. 73–91.

      This review summarizes current research on plant-pollinator networks, stressing the need to include more studies in tropical areas. Tropical areas have a richer diversity in plants and animals than non-tropical areas, resulting in the several network patterns such as low connectance and higher modularity. However, these patterns are overlooked when tropical areas are not equally analyzed, limiting accurate understanding of this relationships.

    2. P. J. Conry, R. Cannarella, “Hawaii statewide assessment of forest conditions and trends: 2010” (Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife, 2010).

      This statewide assessment details the forest conditions of Hawaii in hopes of developing strategies towards conservation. It includes information comparing the major changes in vegetation before and after the arrival of humans on the island.

    3. playback

      A recording of a bird's native calls is played to lure the species into an area.

    4. This would include outplanting commonly consumed native plants (e.g., Pipturus albidus) within plant restoration areas, removing commonly consumed introduced plants in sites with high densities of native fruits, and attracting (e.g., via playback) specific frugivores to restoration sites

      Researcher Sean McDonald placed speakers playing non-native bird calls near native plants in danger of extinction in hopes of attracting these birds to these plants and increasing seed dispersal.

      Read more in Inside Science: https://www.insidescience.org/news/playing-birdsongs-save-trees

    5. Therefore, functional characteristics (e.g., beak, seed, and fruit sizes) and species abundance (39) may be more important in the structure of mutualistic networks than species identity, supporting the role of ecological fitting (40)

      This study found that phenotypical traits such as the size of a bird's beak and the fruit's diameter were strong factors that determined the likelihood of successful interactions, along with species abundance.

    6. For example, in Hawai‘i, large frugivorous birds are absent, resulting in a lack of dispersal of large native fruits (38)

      Islands suffer significant losses of large frugivorous birds due to their small size, isolation from mainlands,and limited amount of species. These large birds tend to be flightless (making them an easy target for predation) and make it possible for large seeded plants, particularly trees, to be dispersed throughout the island.

      More information about the causes and consequences of large frugivorous bird extinction can be found in the Forbes article: https://www.forbes.com/sites/grrlscientist/2018/10/13/does-it-really-matter-if-just-one-species-goes-extinct/#48e3b358610b

    7. We found that specialization, modularity, nestedness, and the simulated robustness in all scenarios to species loss of the O‘ahu networks overlapped with the range of values observed in other networks.

      The results from the simulated extinction, along with the measurement of network interaction patterns (modularity, nestedness, and specialization), were all similar between O'hau and other tropical or non-tropical locations.

    8. We estimated robustness of animals to the extirpation of plants (assuming bottom-up control) and robustness of plants to the extirpation of animals (top-down control). We simulated two scenarios, one in which order of extirpation was random and another—more extreme—scenario in which order was from the most generalist to the most specialist species. After using a null model correction on each metric to account for variation in sampling intensity and network dimensions across studies (14), we compared the 95% confidence intervals for the O‘ahu networks with the global dataset.

      The authors designed hypothetical scenarios where generalist or specialist species in a network went extinct, then determined the severity of these extinctions by measuring the amount of additional species that would (theoretically) go extinct as a consequence.

      The use of a null model ensures that the results found by these simulations are not a coincidence, that is, not due to chance.

    9. weighted

      A weighted network assigns some form of quantitative value to each connection between two partners (an example is shown below in figure 4). In this case, the value assigned was the frequency of interaction.

    10. We assembled and analyzed a dataset of 42 avian SDNs encompassing a broad geographical range, with data from islands (n = 17) and continents (n = 25) in tropical (n = 18) and nontropical (n = 24) areas (table S12). Although some of the other SDNs in the analyses included introduced species [e.g., (7, 34)], SDNs on O‘ahu present an extreme case of dominance by introduced species (>50%), coupled with extinction of all native frugivorous birds

      The authors surveyed data from seed dispersal networks across a variety of habitats, noting that O'ahu was unique in that the majority of its population was mostly made up of introduced species, with the original bird species of the island going extinct.

    11. Abiotic factors

      Non-living parts of an ecosystem, such as elevation or rainfall

    12. Thus, plant-animal networks appear to have distinct links (high interaction rewiring) even when the same species are present in both sites, irrespective of whether networks are dominated by native or introduced species

      The authors conclude that plants and animals at different sites across the island develop their own unique pattern of interactions, whether the sites are populated by mostly native or novel species.

    13. Surprisingly, only 53% of the interaction dissimilarity was due to differences in species composition among sites (βST = 0.30 ± 0.09), whereas 47% was because pairs of species that interacted in one site did not interact in another site where they co-occurred (βOS = 0.27 ± 0.07; fig. S4

      Referring to figure 3, the majority of dissimilarity across sites was due to linkage turnover, represented as the gray bars. This means that even though the sites shared similar species, the interactions were different.

    14. [interaction dissimilarity (βWN) = 0.57 ± 0.11, mean ± SE; n = 21 pairwise sites; Fig. 3 and table S5], indicating that, on average, only 43% of interactions were shared between sites despite the most common bird and plant species occurring at all sites (tables S2 and S3)

      The authors found that the majority of the sites in O'ahu had different sets of interactions between plant and bird species.

    15. We decomposed this metric into two components: species turnover (βST—the proportion of interactions that are not shared owing to differences in species composition between two networks) and linkage turnover [βOS, also called rewiring—the proportion of interactions unique to a single network despite the occurrence of both partners in both networks (30)

      The authors measured the overall dissimilarity between different locations by two factors:

      species turnover when — two  locations do not share similar interaction patterns because they are inhabited by different species,

      and linkage turnover — when species found in both locations develop different interactions specific to their site

    16. The wider variety of partners used at the larger scale (regional network) corresponds to the “fundamental niche,” whereas the subset of partners found at local scales indicates that local populations have much more restricted “realized niches” (27, 28).

      A species' fundamental niche encompasses all of the possible roles it has in its environment, whereas the realized niches are the actual roles that a species plays in its environment, taking into account competition, predation, and other interactions with neighboring species.

      The video below further explains this: https://www.youtube.com/watch?v=-6COob_bymw

    17. Here we show that the interaction patterns recurrently identified in native-dominated networks also emerge in novel mutualistic networks composed of species with little or no shared evolutionary history. This result indicates that prolonged shared evolutionary history is not necessary for the emergence of complex network structure

      The authors concluded that introduced species do not necessarily have to be evolutionarily related to native species to form similar interaction networks. This conclusion was based on their results demonstrating that introduced species on the island successfully formed modular networks comparable to the networks that were formed between native species. 

    18. Furthermore, partner sharing (how distinct species share resources) in SDNs on Oʻahu is structured in a complementary way among bird and plant species, giving rise to distinct modules in which certain birds and plants interact preferentially. The emergence of such structures indicates that these novel SDNs largely reproduce the well-known patterns exhibited in mutualistic networks (18) and that SDN structure is highly conserved, regardless of variation in plant and bird communities.

      The introduced birds and plants integrate successfully into the ecosystem of O'ahu because they follow the same strategies used by the native plants and birds: creating beneficial relationships with specific species and carefully sharing the resources of the island with other organisms. 

    19. We found that despite all interactions being novel and primarily involving introduced species, networks were structurally complex and notably similar between scales (local versus regional) and across sites.

      The authors concluded that overall, the complex network structures of the island's ecosystem on both the local and regional scale remained the same, even though these networks were now infiltrated with invading plant and animal species.

    20. At the local scale, networks had low to intermediate connectance and, unlike the regional network, were not nested. Similar to the regional network, six of seven local networks were specialized and modular, presenting three or four modules (Fig. 2, fig. S3, and table S4)

      At individual sites, the authors again saw species mostly interact with only a subset of the total partners available. 

    21. Consequently, high connectance and nonmodular structures are expected, because both are linked to low specialization [e.g., (14, 23)]

      Dalsgaard and colleagues found that tropical areas have a lot of bird species that are obligate frugivores, meaning that they only eat fruited plants. Because fruit is their sole diet, these birds interact with a large variety of plants to ensure that they're consuming enough food to live.

      This type of behavior is commonly associated with a low specialized network because the birds are not displaying any preference toward any particular plant(s).

    22. supergeneralist

      A species that interacts with a wide number of species in ecological network. 

    23. To what extent are introduced species integrated into seed dispersal networks (SDNs), and do introduced dispersers replace extinct native animals? To investigate these questions, we examined interactions based on 3278 fecal samples from 21 bird species [tables S1 to S3 and (13)] collected over 3 years at seven sites encompassing broad environmental variation across Oʻahu (fig. S1 and table S1).

      With the original bird species extinct, how well does the introduced bird species spread the seeds of native plants? Does this newer bird species show a preference toward introduced species of plants?

      To address these questions, the authors collected poop samples over the course of 3 years from 21 different birds found in 7 different locations across the island of O'ahu. The supplemental figure 1 and table 1 describe the 7 locations' average rainfall, coordinates, and elevation to demonstrate the diversity of these areas. Another set of tables listed the different species and plants (introduced and native) found at each site.

    24. We assessed species interaction patterns via complex network analyses and used four complementary metrics known to vary geographically and reflect community-level responses to major drivers of biodiversity patterns, such as productivity, climatic seasonality, and historical climatic stability [e.g., (14–16)]

      Differences in geography affects the interaction patterns developed between species. Climate change, differences in species richness, and human impact were shown to dictate the types of networks that dominated those areas.

    25. Previous studies have focused on native-dominated communities in which few or no invasive species occur and mutualistic partners have interacted for prolonged periods of time, developing complex and often coevolved interactions (8, 9).

      Bascompte, Jordano, and Olsen investigated coevolutionary interactions across a wide range of locations, measuring the levels of dependence between various species of plants and animals. They showed that most of these interactions are asymmetric, meaning that one species depends more heavily on the relationship than the other. This asymmetry supports high biodiversity and coexistence of multiple species in an ecosystem.

    26. The statistical significance of the observed topological patterns was assessed by contrasting observed values for each metric with the confidence interval from null models (13)

      To determine if an observation is a consequence of a measured phenomenon, and not by chance, researchers must test (and reject) the null hypothesis. A null hypothesis states that a result or observation is due to chance, and so should be disregarded as insignificant. When researchers can reject the null hypothesis, that means their results from a study were not due by chance.

      In this case, the authors test the significance of the identified patterns in the network by comparing these values to a null model, a generated collection of values randomized to produce a pattern based on no ecological mechanism (Gotelli and Graves, 1996). If the observed values differ from the range of null values defined by the null model's confidence interval, they are considered significant.

    27. Thus, although introduced birds are critical for seed dispersal in the ecosystem, they are primarily dispersing introduced plants (only 6.7% of interactions involved native plants).

      The authors concluded that the majority of plants and animals involved in the seed dispersal networks of O'ahu are introduced species, and that the majority of seeds being dispersed by these birds are from introduced plant species.

    28. Oʻahu’s SDN included 15 bird and 44 plant species connected by 112 distinct links (Fig. 1)

      The authors identified 44 different plant species and 15 different birds in O'ahu. Figure 1 depicts each bird (left column) and each plant (right column) as rectangles. The lines connecting a bird to a plant represent a seed dispersal event.

    29. Oʻahu, in particular, is among the areas most affected by extinctions and biological invasions in the world (12)

      In a 2010 Hawaii statewide assessment of forest conditions and trends, a map illustrated that major vegetation types for multiple islands, especially O'ahu, experienced severe changes in comparison to before the arrival of humans.

    30. Most native Hawaiian forest plants are bird-dispersed, yet no native dispersers remain in most ecosystems (10, 11). Thus, seed dispersal is almost entirely dependent on a handful of introduced vertebrate dispersers, nearly all of which are birds (10, 11).

      The introduction of novel seed dispersers (aka birds) is an important factor regarding in the survival of native Hawaiian plant species. One study showed that the distribution of seeds from native plants is becoming increasingly dependent on not native but foreign birds. C. Chimera and D. Drake also found that these introduced birds tended to spread more seeds from non-native plants rather than native plants.

    31. Hawaiʻi provides an opportunity to investigate the consequences of an extreme scenario of loss of native species and their replacement by non-native species.

      Native plants on the Hawaiian island of Kauai are threatened by changing climate, invasive species, and destruction by feral pigs. Efforts led by the Plant Extinction Prevention Program (PEPP) are working toward saving these endangered species and preventing the loss of further species.

      Read more in the grist: https://grist.org/article/hawaiis-rarest-plants-are-in-crisis-meet-the-people-fighting-to-save-them/

    32. Mutualistic plant-animal networks are particularly susceptible to species loss (5) and invasions (4, 6, 7)

      A mutualistic network is a web of beneficial partnerships between organisms. Disturbances to that relationship, like from one of the organisms becoming extinct, or by the intrusion of another species, can be harmful for the original partners of that relationship.

    33. As a result, “novel communities” have emerged, characterized by a reshuffling of species, changes in species interactions, and, in some cases, alteration or disruption of ecosystem services maintained by these interactions (3, 4)

      Brodie et al. reviews the concept of secondary extinction, the idea that the extinction of a species, caused by human activity, can lead to the loss of additional species.

      Below is a diagram from the review depicting different types of secondary extinctions. Co-extinction is when the direct impact of humans (red arrow) leads to the loss of one species, causing the loss of another species, which can then cascade into a series of extinctions. Human activity (yellow arrows) also affects interactions between species (gray arrows).

    34. J. Memmott, N. M. Waser, M. V. Price, Tolerance of pollination networks to species extinctions. Proc. R. Soc. London Ser. B 271, 2605–2611 (2004). doi:10.1098/rspb.2004.2909pmid:15615687

      By simulating the network patterns between plants and pollinators, the authors demonstrated that plants were more resistant to extinction with the removal of specialized pollinators versus generalized pollinators. Specialized pollinators only interact with a few plant species, whereas generalized pollinators interact with a larger range of plant species. When a generalized pollinator is lost, more plants are affected.

    35. N. Blüthgen, F. Menzel, N. Blüthgen, Measuring specialization in species interaction networks. BMC Ecol. 6, 9 (2006). doi:10.1186/1472-6785-6-9pmid:16907983

      Previously, the majority of network analysis was qualitative. Blüthgen et al introduce two quantitative measurements that uses the frequency of interactions to describe specialization at the species level and across a network.

    36. S. Culliney, L. Pejchar, R. Switzer, V. Ruiz-Gutierrez, Seed dispersal by a captive corvid: The role of the ‘Alalā (Corvus hawaiiensis) in shaping Hawai‘i’s plant communities. Ecol. Appl. 22, 1718–1732 (2012). doi:10.1890/11-1613.1pmid:23092010

      This study provides evidence that ‘Alalā, an endangered, native bird species in Hawaii, displays seed dispersal behaviors and promotes seed germination of various native plants. Based on these results, the authors suggest that ‘Alalā can contribute towards the restoration of native fruiting plants in Hawaiian forest communities.

    37. E. C. Fricke, J. J. Tewksbury, E. M. Wandrag, H. S. Rogers, Mutualistic strategies minimize coextinction in plant-disperser networks. Proc. Biol. Sci. 284, 20162302 (2017). doi:10.1098/rspb.2016.2302pmid:28490622

      Fricke et al investigates how well mutualistic systems between plants and animals protect against coextinction. They find that the diversity in partners protects species in mutualistic interactions because they do not rely solely on one or few partners for survival.

    38. ↵ S. L. Lewis, M. A. Maslin, Defining the Anthropocene. Nature 519, 171–180 (2015). doi:10.1038/nature14258pmid:25762280

      The Anthropocene defines the epoch or geological time when human activity significantly impacted the global environment. Based on the criteria for defining a new epoch and supporting geological evidence, the authors propose two possible dates to mark the beginning of the Anthropocene: 1610 and 1964

    39. H. A. Mooney, E. E. Cleland, The evolutionary impact of invasive species. Proc. Natl. Acad. Sci. U.S.A. 98, 5446–5451 (2001). doi:10.1073/pnas.091093398pmid:11344292

      Mooney and Cleland describe the evolutionary consequences of invasive species on the invaders themselves and on native species. Modifying behavior to adapt to a new environment, competing for similar resources, predation, or creating hybrid progeny by breeding with natives species are just a few examples.

    40. A. de Almeida, S. B. Mikich, Combining plant–frugivore networks for describing the structure of neotropical communities. Oikos 127, 184–197 (2018). doi:10.1111/oik.04774

      The authors merged data sets from multiple studies investigating fruit-frugivore interactions and illustrated that most networks across various neotropical areas were significantly nested and modular. The authors also concluded that combining results from different studies can be useful for analyzing the ecological structures of broad regions, and supporting conservation efforts.

    41. E. Burgos, H. Ceva, R. P. J. Perazzo, M. Devoto, D. Medan, M. Zimmermann, A. María Delbue, Why nestedness in mutualistic networks? J. Theor. Biol. 249, 307–313 (2007). doi:10.1016/j.jtbi.2007.07.030pmid:17897679

      Nestedness can contribute towards the robustness of a network. If species that share fewer interactions are the first to go extinct, the remaining mutualistic system have a greater chance of survival. The authors also calculate a coefficient as a parameter of a network’s robustness.

    42. E. L. Rezende, J. E. Lavabre, P. R. Guimarães, P. Jordano, J. Bascompte, Non-random coextinctions in phylogenetically structured mutualistic networks. Nature 448, 925–928 (2007). doi:10.1038/nature05956pmid:17713534

      The phylogenetic or evolutionary relationship between species can predict the types and quantity of interaction patterns they exhibit in a network. Using a simulation of extinction events, the authors also demonstrated that the extinction of one species can result in the extinction of others species that are evolutionarily related.

    43. A. Traveset, J. M. Olesen, M. Nogales, P. Vargas, P. Jaramillo, E. Antolín, M. M. Trigo, R. Heleno, Bird-flower visitation networks in the Galápagos unveil a widespread interaction release. Nat. Commun. 6, 6376 (2015). doi:10.1038/ncomms7376pmid:25757227

      The authors studied the feeding behaviors of birds in the Galapagos island. They discovered that these birds ate a not just a select few, but a wide variety of plants on the island. They called this behavior interaction release, a survival tactic where animals expand their niche.

    44. C. G. Chimera, D. R. Drake, Patterns of seed dispersal and dispersal failure in a Hawaiian dry forest having only introduced birds. Biotropica 42, 493–502 (2010). doi:10.1111/j.1744-7429.2009.00610.x

      In contrast to Foster, Chimera found that introduced birds in Hawaii dispersed predominately the seeds of non-native plants. Possible explanations could be that the non-native plants produce larger fruit, that are more abundant and have a smaller seed size. These qualities are more enticing to birds and enhance the plants’ chances of getting eaten and later deposited.

    45. J. T. Foster, S. K. Robinson, Introduced birds and the fate of Hawaiian rainforests. Conserv. Biol. 21, 1248–1257 (2007). doi:10.1111/j.1523-1739.2007.00781.xpmid:17883490

      Foster and colleagues investigated how often introduced, fruit-eating birds on the islands of Hawaii consume and disperse seeds from native plants versus seeds from exotic plants. They found that seeds from native plants made up the majority of the introduced bird species’ diets. This supports the potential of introduced bird species playing a role in the conservation efforts of native habitats.

  2. Jul 2021
  3. Jun 2021
    1. Several studies suggest that the phylogenetic relationships of species contribute to structuring mutualistic networks

      Normally depicted as the "tree of life" (shown below), the phylogenetic tree traces the genetic lineage of organisms over time. Two species share a phylogenetic relationship when they share a common ancestor. An example of a phylogenetic tree can be found at https://www.nationalgeographic.org/media/tree-life/

      The authors of the cited paper found that phylogenetic relationships can influence the type of networks species build and explain the type of species involved in these interactions.

    2. The regional network had low connectance, moderate specialization, and nested and modular topologies, with three distinct modules (Fig. 1, fig. S2, and table S4).

      When studying larger areas of the island, the authors observed that species engaged in only a small portion of the possible interactions available, with groups of species specifically interacting amongst each other.

    3. niche broadening

      A niche is an organism's role in its ecosystem, describing how it utilizes the resources and interacts with living and nonliving factors of its environment.

      Niche broadening is when a species expands its roles in its habitat to enhance its chances of survival.

    4. seed dispersal events

      The distribution of a seed by being eaten by an animal and later excreted in its feces.

    5. mitigate the impacts of extinctions and invasions on ecosystem functions.

      In another study taking place in Hawaii, researchers are investigating invasive predators such as the black rat to implement protective measures for native bird populations of the Hawaii Volcanoes National Park. More on this study can be found here: https://www.usgs.gov/centers/pierc/science/monitoring-bird-and-rat-behavior-improve-invasive-species-management?qt-science_center_objects=0#qt-science_center_objects

    6. Our findings suggest that shared evolutionary history is not a necessary process for the emergence of complex network structure, and interaction patterns may be highly conserved, regardless of species identity and environment.

      Invasive species can maintain interactions and behaviors with their surroundings similar to the native species they replaced, even if both species are not related.

    7. introduced species

      A group of living organisms that has recently moved into a new ecosystem

    8. To investigate how such changes affect communities, we performed multiscale analyses of seed dispersal networks on Oʻahu, Hawaiʻi.

      The authors visited multiple areas in Hawai'i to study how seeds from plants (originally from the area or recently introduced) were being distributed by invasive birds.

    9. Increasing rates of human-caused species invasions and extinctions may reshape communities and modify the structure, dynamics, and stability of species interactions.

      The spread of invasive species (living organisms not originally found in a specific ecosystem) causes disruptions to wildlife in a variety of ways. Some examples include outcompeting native plants or animals for resources and food, or carrying diseases harmful to native species. More information on this topic can be found at NWF's "Invasive Species": https://www.nwf.org/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Invasive-Species

  4. Jul 2019
    1. High interaction dissimilarity has also been reported in specialized, native-dominated pollination networks, even between spatially close networks (33)

      D. Carstensen and others quantified the variability of interactions between plants and pollinators across different spaces. They found that these interactions vary greatly between different locations due to the abundance of species, which determined the likelihood of partners interacting with each other.

  5. Jun 2019
    1. For example, both fleshy-fruited plants and frugivores on islands tend to have wide niches owing to resource limitation

      Traveset and colleagues observed that bird-plant interactions on the Galápagos islands are highly generalized, meaning the birds developed relationships with a wide variety of plants, and vice versa. These broad interactions offer more opportunities for species to gain food. However, the authors also warn that these additional interactions promote the reproduction and survival of invasive plant species, at the cost of native species.

    2. interaction release

      In response to lack of food and increased populations, animals broaden the scope of species they interact with beyond their original interactions.

    3. frugivores

      An animal that eats primarily fruit

    4. interaction dissimilarity

      When the behavior between species in one area differs from the behaviors between species in another location.

    5. novel interactions

      A new relationship or pattern of behavior between plants and animals.

    6. This high degree of similarity between novel and native-dominated networks suggests that the processes that structure interactions in such communities are largely independent of species identity and that ecological filtering occurs over relatively short (ecological) time, leading to functionally similar sets of players as compared with systems that have long evolutionary histories

      The authors concluded that novel species' interactions, developed over a relatively short period of time, still resemble much older interactions between native species.

    7. binary

      Binary calculations are a straightforward form of measurement that states the presence or absence of an interaction.

    8. However, the lack of association between rewiring and examined factors indicates that birds and plants in the system are highly flexible and can switch partners, irrespective of abiotic conditions and the identity of species in the community.

      The authors found that neither abiotic (rainfall and elevation) nor biotic (invasive species) factors influenced the variations in plant and animal interactions measured from different sites with similar species populations.

    9. pecifically, interaction dissimilarity and the dissimilarity caused by species turnover were influenced by elevation and rainfall, but not by percent of introduced plant species (tables S6 to S9). This suggests that the environment indirectly influences interactions via effects on species distributions, including the distribution of introduced species.

      Results in the supplement section show that abiotic factors (rainfall and elevation) affected the composition of species found at a site, thereby creating different network interactions between sites.

    10. biotic factors

      Living parts of an ecosystem, in this case, invasive species on the island

    11. To examine interaction dynamics across sites and to test their association with environmental variables, we calculated the dissimilarity (interaction turnover) between pairs of networks, using data limited to species present in the networks.

      The authors compared the similarities and differences between species' interactions across different locations around the island, taking into account the unique environments of each site.

  6. May 2019