Importance and Applications of Habitat Connectivity. As anthropogenic actions continue to impact populations, communities and ecosystems,

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1 Christine Caron NRS 534 Dr. August May 18, 2005 Importance and Applications of Habitat Connectivity As anthropogenic actions continue to impact populations, communities and ecosystems, habitat loss and increased habitat fragmentation make connectivity between these habitats crucial to examine for monitoring, maintaining, and managing species. There are many studies that show strong evidence that greater connectivity is beneficial to species. One example is Wilson s (2004) work in the Chilean rainforest studying Chucao Tapaculos (Scelorchilus rubecula). This particular bird species is unlikely to leave dense forest cover to use open fields to travel between habitats, but will use densely vegetated corridors. In this study, she examined well connected (> 20 m wide) and poorly connected (<5 m wide) habitats and found that juvenile retention was higher in poorly connected habitats (21% in poorly connected vs. 3% in well connected ) which may increase the risks of inbreeding. There was also an increased probability of unmated males in the forest fragments that were poorly connected (18% in poorly connected vs. 1% in well connected) which might be an indication that these areas suffer from high dispersal costs due to risk of predation (Wilson 2004). Conserving existing connections and managing for increased connectivity would clearly benefit this population. Clevenger et al. (2001) also address the importance of connectivity, but in this case via corridors not typical of natural habitats: culverts. As many roads become barriers to animal movement, exploring the functionality of culverts as passages between habitats becomes important. The authors found that traffic volume, noise levels and road width were highly ranked as factors affecting use of culverts by various species. To maximize the connectivity for many small and medium sized mammals, such as martens, snowshoe hares, red squirrels,

2 coyotes, and weasels, they suggest that road construction designs should factor in frequently spaced culverts of varying sizes with ample vegetation cover near the entrances (Clevenger et al. 2001). Berggren et al. (2001) note the importance of connectivity as well in their study of Roesel s bush-crickets (Metrioptera roeseli). By introducing members of this species in areas of varying connectivity that were not previously inhabited by this species, they discovered reduced population growth in isolated fragments and limits on individuals to return to the habitat at which they were introduced. The authors argue that greater connectivity can help reduce the negative effects of unsuitable habitats and that availability to move between habitats is especially important at this colonization stage (Berggren et al. 2001). In the work of Tiebout and Anderson (1997), their models of populations of the Florida Scrub Lizard (Scleoporus woodi) indicate that connectivity of fragments is important for these particular habitat specialists that require open, sunny scrub habitat. According to the models, scrub lizards in poorly connected habitats would only have a 26.5% chance of colonizing new habitat if the current habitat were to become unsuitable. The authors suggest that a staggered approach might be worth considering, altering the clear cutting regime, so that when one habitat becomes unsuitable, a corridor becomes available that connects to the next habitat, and the patch and the corridor do not become unavailable at the same time. The difficulty in this strategy is that it could compete with maintaining the connectivity between old-growth stands in the area. This study in part indicates that using corridors is not a general solution to current problems of reduced connectivity as the larger context may play a role as well as the way that species use the habitat (Tiebout and Anderson 1997). Connectivity not only has importance for existing adult populations, but also for movement between juvenile and adult habitats, as explored in Gillanders et al. (2003). As a result of their literature review, they found that little is known about the movement of marine fauna from juvenile to adult habitats, as few studies have focused directly on this topic. However, they note that with the continuing elimination of habitats and increased fragmentation

3 as a result of human activity, an understanding of the movement between these habitats and of which juvenile populations contribute the most to adult population is important for maintaining corridors and existing adult populations (Gillanders et al. 2003). In addition to maintaining population dynamics with connectivity, there may also be genetic consequences that arise from levels of connectivity in habitats. In a study of the bird species, capercaille (Tetrao urogallus), Segelbacher et al. (2003) found lower genetic diversity in isolated habitats, as anthropogenic disturbances have contributed to reduced gene flow between populations. In this case lower levels of connectivity may impact not only the sustainability of population size, but may have genetic consequences, such as inbreeding (Segelbacher et al. 2003). However, there may be other factors to consider when looking at the genetic effects of isolation. For example, the Oregon Chub on Oregon s Willamette River has larger populations that are supported in the isolated areas with lower connectivity, because flooding and connectivity promotes dispersal of nonnative species that lower the chub population density (Scheerer 2002). While this data indicates that connectivity has a negative effect on the population size of Oregon chub, these fish historically existed in flooding conditions that favored dispersal. In this case, there appears to be a tradeoff between population size and the possible genetic implications that could result from strategies that contradict their evolutionary life history in favor of population size (Scheerer 2002). Similar results were shown in zooplankton in experimental populations by manipulating habitat connectivity by Forbes and Chase (2002) where they found increased connectance resulted in a decrease in diversity of species regionally and an increase in percent similarity within the individual communities. The result may be due to greater establishment of common species with greater connectivity and a resulting extinction of rare species. A decrease in habitat diversity with increasing corridors is most likely where heterogeneous habitats are present (Forbes and Chase 2002). Another marine study that shows species benefiting from less habitat connectivity is Nanami and Nishihira s (2003) work on fishes in Okinawan coral reefs. Working at a small

4 spatial scale (within 32 m 2 ) and transplanting branching coral colonies to isolated sandy sea bottom and contiguous rocky reef flat habitats, they found that species richness, abundance and rate of increase were significantly greater in the isolated habitat. Although they admit that they are unsure if the same will be true at a duration longer than nine months or at a larger spatial scale (Nanami and Nishihira 2003). The trophic level being addressed may also be a factor in determining the potential benefits or consequences of habitat connectivity. While Steffan-Dewenter (2003) did find increase in density of bees with increased habitat connectivity, an important factor for habitat specialists, this pattern was not present in the plant species, suggesting that plants, at a lower trophic level were not as greatly affected by landscape context (Steffan-Dewenter 2003). In contrast to this idea, Lindborg and Eriksson (2004) show strong evidence that supports the impact of landscape context on plant species as well. However, in this case, the confounding variable was that of time. They found that habitat connectivity did not affect present day plant species richness or density, but that at large spatial scales (1 km and 2 km radius) and temporal scales of 50 and 100 years ago, connectivity did affect species richness and density, just with a time lag (Lindborg and Eriksson 2004). This gives managers and conservationists one more aspect to take into consideration, although the authors do speculate that this time lag would be less likely in shorter lived species and species at higher trophic levels (Lindborg and Eriksson 2004). The current literature gives those working on environmental monitoring, management and conservation much to think about. There is a vast amount of information that supports greater habitat connectivity to offset habitat loss and habitat fragmentation. However, there is also much evidence that shows how important it is to consider the context of the particular species that is being managed for, the habitat needs, genetic implications, presence of invasive species, spatial scale, population size, temporal scale, other species affected, and possibly even more factors to consider. Thus, continuing to gain a better understanding of species,

5 particularly those that may be at risk, and putting in place environmental monitoring to keep track of the effects of management actions are extremely important.

6 Annotated Bibliography Berggren, A., A. Carlson, and O. Kindvall The effect of landscape composition on colonization success, growth rate and dispersal in introduced bush-crickets Metrioptera roeseli. Journal of Animal Ecology 70: With increased habitat loss and fragmentation a continuing problem, this paper presents the classic connectivity is good argument, as decreased connectivity prevents movement between patches. In their study of Roesel s bush-crickets (Metrioptera roeseli), the crickets are introduced in 70 habitats of varying connectivity. They found that population growth was reduced in isolated areas, as the connectivity increases access to a wider habitat spectrum. The larger growth rates occurred in populations less isolated from good habitat initially. Isolation can also limit the ability of individuals to return back to the patch at which they were introduced. The authors argue that increasing connectivity for this species can also reduce the negative effects of unsuitable habitats, such as forest. Availability to move between patches proves especially important for introduced population survival and establishment. Clevenger, A. P., B. Chruszcz, and K. Gunson Drainage culverts as habitat linkages and factors affecting passage by animals. Journal of Applied Ecology 38: This study addresses an increasingly important issue with increasing urbanization: the effects of roads on populations and the potential usefulness of culverts as corridors for mammals. The authors found that traffic volume, road width, and noise levels were most likely to affect a species use of culverts. American martens, snowshoe hares and red squirrels used the culverts more with greater traffic volume, although coyotes use culverts less with increased traffic volume. Coyotes, snowshoe hares, and red squirrels all showed negative influences of increasing noise and road width on their usage of culverts. Weasels and martens were also affected by the structure of culverts, such as height and openness and vegetation cover near culverts positively affected passage in culverts of weasels and snowshoe hares. In current situations where more and more roads are being built, creating road construction that includes culverts frequently spaced of different sizes with vegetation cover could maximize connectivity for small and medium sized animals in these habitats. Forbes, A. E. and J. M. Chase The role of habitat connectivity and landscape geometry in experimental zooplankton metacommunities. Oikos 96: This zooplankton study focuses on aquatic systems at the small scale. One of the interesting points that stands out here is the use of fuzzy tennis balls moved between plastic containers to manipulate habitat connectivity (via amount of dispersal among patches). The results of Forbes and Chase s work produced no effect on local species diversity with increased connectance, but an overall decrease in the diversity of species within regions of experimental communities that were connected. Percent similarity among communities also increased as connectance did the communities became more similar to each other, and species diversity within the entire region declined. This might be because increased connectance enabled common species to establish in all mesocosms, resulting in extinction of rare species. With increasing connectance, the population of Ceriodaphnia reticulata reached higher densities in all mesocosm types and may partially explain the increase in percent similarity. Based on this work, it is important to

7 note how corridors factor in to a particular conservation strategy, as regional diversity may decrease in areas where heterogeneity among habitat fragments is present. Gillanders, B. M., K. W. Able, J. A. Brown, D. B. Eggleston, and P. F. Sheridan Evidence of connectivity between juvenile and adult habitats for mobile marine fauna: an important component of nurseries. Marine Ecology Progress Series 247: The focus of this paper was a review of the literature on movement between juvenile and adult habitats, an interesting deviation from a number of other connectivity papers. The authors included 110 studies, but came up with only 13 that showed good evidence of movement between juvenile and adult habitats. The reasons for such a low number were because not all studies were directed at answering these types of questions or focused on only one stage of life history, not both juvenile and adult. They note that just because organisms are no longer found in juvenile habitats does not necessarily mean that they have successfully moved to adult habitats. As human activities lead to continued elimination and fragmentation of habitats, it becomes increasing important to understand the connectivity between and movement from juvenile to adult habitats, as failing to protect these corridors could have significant consequences on adult populations. The major need for monitoring and assessment to maintain adult populations is to measure the movement of individuals to understand the life cycle better and to determine which juvenile habitats contribute the most to adult populations to help direct conservation efforts. Lindborg, R. and O. Eriksson Historical landscape connectivity affects present plant species diversity. Ecology 85: This particular paper is one of very few that examines connectivity in plant communities and is also unique in its focus on the temporal scale in addition to just the spatial scale. The authors note that colonization and extinction rates may be affected by site connectivity. They examined the total species richness and species density of 30 grassland sites, analyzing present maps and maps from 50 and 100 years ago at 1 km and 2 km radius scales. The findings showed that the present landscape was not related to species richness or density at either spatial scale, but rather that both richness and density were related to the connectivity of the landscape 50 years ago (at the 1 km scale) and 100 years ago at the 1 km and 2 km spatial scale. This paper points out that considerable time lags can occur between changing habitats and response of the populations in that habitat, causing extinctions in the future, or perhaps giving threatened species time to recover. Although this time lag may not be present in short lived or more mobile organisms, the paper points out the importance of assessing landscape transformation at temporal, as well as spatial, scales, a concept lacking from most other studies. Nanami, A., and M. Nishihira Effects of habitat connectivity on the abundance and species richness of coral reef fishes: Comparison of an experimental habitat established at a rocky reef flat and at a sandy sea bottom. Environmental Biology of Fishes 68: This study stands out from some of the other studies of habitat connectivity for a number of reasons. First, the authors find that isolated patches (rather than continuous with greater connectivity) are preferred by coral reef fish in Okinawa, at least at a small spatial scale (within 32m 2 ). Second, this study focuses on a marine environment which is less commonly found in

8 the literature than terrestrial habitats. Finally, for this research, they transplanted branching coral colonies to better compare the differences between isolated sandy sea bottom and contiguous rocky reef flat habitats, as these particular habitats would be difficult to compare objectively in their natural conditions. The authors found that species richness, abundance and rate of increase in abundance were significantly greater in the isolated habitat, although they note that others have found that this trend does not exist at larger spatial scales (>200 m 2 ) and that they are unsure whether or not a duration longer than the 9 months of this study would produce the same results. Regardless, this study is important in pointing out that connectivity of coral reef habitats affects species richness and abundance for the fish species there, and that at least at a small scale, isolated habitats are more attractive. Scheerer, P. D Implications of floodplain isolation and connectivity on the conservation of an endangered minnow, Oregon Chub, in the Willamette River, Oregon. Transactions of the American Fisheries Society 131: Population sizes of Oregon chub on the Willamette River in Oregon were examined in isolated and connected habitats, and in these populations, the author found that the fish were most abundant in isolated habitats. This study is interesting because it seems counterintuitive to the idea that greater connectivity increases population size. However, in this area, human practices have created a situation where flooding events and greater connectivity of floodplains allows for invasion of habitats by nonnative fish species that result in substantial declines of Oregon chub, without recolonization. Historically, the Oregon chub used floods as an opportunity for dispersal and genetic exchange before the conditions favored instead the dispersal of nonnative species. This study shows that Oregon chub will maintain higher population sizes in isolated habitats, but that there may be genetically implications, as isolation is contrary to their evolutionary life history. This work demonstrates how important an understanding of the effect of each habitat characteristic is on a particular species in a particular area, given all the influencing factors. Segelbacher, G., J. Hoglund, and I. Storch From connectivity to isolation: genetic consequences of population fragmentation in capercaille across Europe. Molecular Ecology 12: Connectivity of habitats was shown in this study to have significant effects on the genetics of the population of a particular bird species, the capercaille (Tetrao urogallus) in fragmented habitats in Europe. Isolated habitats showed the lowest allelic richness, indicating that maintaining connectedness is important to sustaining high levels of genetic diversity. Much of the habitat fragmentation in this region has been do to anthropogenic activities, reducing the gene flow between populations. Although demographic models indicated a population of 500 birds in the minimum viable size, the authors found obvious signs of reduction in genetic variation in populations of up to 1000 birds. The reduction of genetic diversity in isolated populations may have genetic (inbreeding) and evolutionary (formation of new species or subspecies) consequences, indicating the importance of maintaining connectivity between local fragmented populations, a major challenge. This paper makes an important contribution in that it clearly shows that the landscape context can affect species, not only at the population level, but on the molecular level as well.

9 Steffan-Dewenter, I Importance of habitat area and landscape context for species richness of bees and wasps in fragmented orchard meadows. Conservation Biology 17: In this study, several characteristics are examined: habitat area, habitat connectivity, and landscape context. Studies were conducted in 45 fragmented orchard meadows studying bees, wasps, and their natural enemies. Although the author shows habitat area to be the most important factor in this context, habitat connectivity did affect some groups. In this situation, effects were only seen at small spatial scales (250 m) radius, likely due to short foraging distances. In support of the trophic-level hypothesis, he finds that plants at the lowest trophic levels did not show species area relationships, suggesting that plants are less affected by landscape context. It is interesting that although habitat connectivity did not have significant effects on the species richness of bees, sphecid wasps, and natural enemies, connectivity did increase local population densities, and greater connectivity negatively impacted eumenid wasps, possibly due to greater competition for nesting sites with increasing bee abundance. The author notes that habitat specialists may depend more on the connectivity between local habitats, but that for habitat generalists, conservation of resources within the landscape matrix may be more related. Monitoring of bees and the consequences of habitat characteristics on their populations is important due to their importance as pollinators and potential of disruption in plant-pollinator dynamics. Tiebout III, H. M., and R. A. Anderson A comparison of corridors and intrinsic connectivity to promote dispersal in transient successional landscapes. Conservation Biology 11: Modeling the various impacts of intrinsic (natural) and extrinsic (artificially created) connectivity on the Florida Scrub Lizard (Scleoporus woodi) was the focus of Tiebout and Anderson s work in this study. As habitat specialists that require open, sunny scrub, the author s suggest that scrub lizards living in poorly connected landscapes would have only a 26.5% chance of colonizing a new habitat when the current patch became unsuitable; however, generalist species living in well connected habitats could always colonize new sites when needed. Of particular interest in this paper is the authors critique of typical corridor model conservation approaches, which might not apply if the patches and the corridors that connect them become unsuitable at the same time. They suggest that in this environment where clear cutting serves as a major disturbance factor, that staggering the timing so that as a patch becomes unsuitable, a corridor is created that leads to a newly created suitable habitat. The difficulty in this strategy is that it may compete with maintaining connectivity between old-growth stands. Even attempting to develop levels of intrinsic connectivity with management practices may be problematic as levels too low may strand populations and levels too high could produce edge effects. This work points out that the use of corridors is not a general solution as there are many logistical design problems to be resolved, but it demonstrates the need for monitoring and understanding the varying nature of connectivity in many complex landscape types. Wilson, M. F Loss of habitat connectivity hinders pair formation and juvenile dispersal of Chucao Tapaculos in Chilean rainforest. The Condor 106: This paper clearly shows some of the problems associated with poor habitat connectivity that can negatively impact population dynamics. In many situations, a consequence of forest fragmentation is loss of connectivity among the remaining forest patches, and in bird

10 populations corridors are often important for maintaining population structure. The author examines a population of Chucao Tapaculos (Scelorchilus rubecula) in Chile, a species that is usually reluctant to leave dense forest for open fields, but uses corridors. She examined well connected and poorly connected fragments and found higher juvenile retention and increased probability of unmated males in poorly connected fragments. Populations in the poorly connected fragments may have higher risk of inbreeding or suffer higher predation rates. The author suggests that greater connectivity can prevent some of the negative effects of fragmentation for this species and that creating networks of woodlots, wooded ravines, and sea cliffs would help the chucaos and other species to occupy more of the available habitats in the area.