The association of Lantana camara with elephant (Elephas maximus), their food, habitat use and feeding behaviour in southern India

<p>Invasive exotic species pose an enormous threat to the world's biological diversity. Invasions can alter native communities, replacing local biotas with non-indigenous species introduced by humans. Exotic plant invasions can have negative effects on native flora, which can be in turn detrimental to the herbivores that depend on the vegetation. In this dissertation, I examined the association of an exotic invasive weed, Lantana camara L., with the Asian elephant (Elephas maximus), its food resources (grass and browse), habitat use and feeding behaviour in Mudumalai Tiger Reserve, southern India. Exotic plant invasions are often associated with alterations or declines in native floral species. I first examined the association of L. camara and measured environmental covariates with floral species assemblage and richness, elephant browse plants, percentage grass cover and percentage grass occupancy. A multivariate analysis revealed a significant association of L. camara with floral species assemblage and richness, some elephant browse plants and grass cover within the moist deciduous forest (MDF) and dry deciduous forest (DDF), but not in the thorn forest (TF) of Mudumalai. My results suggest that L. camara appears to be capable of altering the floral community in some habitats. These results also suggest that changes in the floral community and a reduction in grass cover due to L. camara invasion could be detrimental to elephant and other herbivores that depend on grass in this reserve. I then examined the association of L. camara with habitat use by elephant. Elephant dung density was used to assess elephant habitat use from 62 line transects, each 1-km in length. I found no evidence that L. camara was associated with elephant habitat use across habitats, although the interaction term between one habitat (DDF) and L. camara was significantly associated with elephant dung density suggesting that the effect of L. camara was different in different habitats. This indicates that L. camara is associated with elephant habitat use within certain habitats. Habitat and impact of human settlements were significantly associated with elephant habitat use across habitats within Mudumalai. In the DDF, however, only L. camara was associated with elephant habitat use. I conclude that while no significant effects of L. camara were seen across habitats, in specific habitats, negative associations of this invasive plant with elephant habitat use, possibly through the reduction of grass cover, are possible. These results indicate that L. camara appears detrimental to elephant in certain habitats and removal of L. camara in these habitats should be prioritised so as to facilitate growth of grass and native browse species, especially if elephant populations continue to expand. Lastly, I examined the association of elephant behaviour, assessed from feeding and stepping rates, with variation in L. camara invasion. Fifty-seven elephants were observed for a total of 64.3 hours using the focal-animal sampling method. Elephant were never observed to feed on L. camara, but rather fed on grass and browse that were present within and around L. camara patches. Feeding rates (number of trunksful·min⁻¹) were negatively associated with L. camara invasion. A path analysis, which assesses both direct and indirect effects of independent variables, indicated that the total effect of L. camara on feeding rates was 11% less than the direct negative association owing to a positive indirect relationship between L. camara and feeding rates through grass cover and browse density. Lantana camara was not significantly associated with variation in stepping rates (number of steps·min⁻¹). Rather, stepping rates were negatively associated with grass cover and positively associated with browse density. My results indicate that L. camara is potentially capable of changing elephant feeding rates, likely through a loss of grass areas due to L. camara invasion. Wild elephants do not eat L. camara, and this invasive plant appears to take the place of an important food source. My results indicate that managers should prioritize their focus on certain habitats to control the impact of L. camara on elephants and vegetation. However, this study was of a correlational nature based on observational data. Experimental work is therefore needed to test for causal relationships among the variables I measured, over multiple seasons and in different habitats. Experimental evidence will enhance our understanding of how invasive weeds modify floral communities, elephant habitat use and behaviour and help determine whether L. camara is a 'passenger' or 'driver' of these changes in this ecosystem.</p>

The association of Lantana camara with elephant (Elephas maximus), their food, habitat use and feeding behaviour in southern India

<p>Invasive exotic species pose an enormous threat to the world's biological diversity. Invasions can alter native communities, replacing local biotas with non-indigenous species introduced by humans. Exotic plant invasions can have negative effects on native flora, which can be in turn detrimental to the herbivores that depend on the vegetation. In this dissertation, I examined the association of an exotic invasive weed, Lantana camara L., with the Asian elephant (Elephas maximus), its food resources (grass and browse), habitat use and feeding behaviour in Mudumalai Tiger Reserve, southern India. Exotic plant invasions are often associated with alterations or declines in native floral species. I first examined the association of L. camara and measured environmental covariates with floral species assemblage and richness, elephant browse plants, percentage grass cover and percentage grass occupancy. A multivariate analysis revealed a significant association of L. camara with floral species assemblage and richness, some elephant browse plants and grass cover within the moist deciduous forest (MDF) and dry deciduous forest (DDF), but not in the thorn forest (TF) of Mudumalai. My results suggest that L. camara appears to be capable of altering the floral community in some habitats. These results also suggest that changes in the floral community and a reduction in grass cover due to L. camara invasion could be detrimental to elephant and other herbivores that depend on grass in this reserve. I then examined the association of L. camara with habitat use by elephant. Elephant dung density was used to assess elephant habitat use from 62 line transects, each 1-km in length. I found no evidence that L. camara was associated with elephant habitat use across habitats, although the interaction term between one habitat (DDF) and L. camara was significantly associated with elephant dung density suggesting that the effect of L. camara was different in different habitats. This indicates that L. camara is associated with elephant habitat use within certain habitats. Habitat and impact of human settlements were significantly associated with elephant habitat use across habitats within Mudumalai. In the DDF, however, only L. camara was associated with elephant habitat use. I conclude that while no significant effects of L. camara were seen across habitats, in specific habitats, negative associations of this invasive plant with elephant habitat use, possibly through the reduction of grass cover, are possible. These results indicate that L. camara appears detrimental to elephant in certain habitats and removal of L. camara in these habitats should be prioritised so as to facilitate growth of grass and native browse species, especially if elephant populations continue to expand. Lastly, I examined the association of elephant behaviour, assessed from feeding and stepping rates, with variation in L. camara invasion. Fifty-seven elephants were observed for a total of 64.3 hours using the focal-animal sampling method. Elephant were never observed to feed on L. camara, but rather fed on grass and browse that were present within and around L. camara patches. Feeding rates (number of trunksful·min⁻¹) were negatively associated with L. camara invasion. A path analysis, which assesses both direct and indirect effects of independent variables, indicated that the total effect of L. camara on feeding rates was 11% less than the direct negative association owing to a positive indirect relationship between L. camara and feeding rates through grass cover and browse density. Lantana camara was not significantly associated with variation in stepping rates (number of steps·min⁻¹). Rather, stepping rates were negatively associated with grass cover and positively associated with browse density. My results indicate that L. camara is potentially capable of changing elephant feeding rates, likely through a loss of grass areas due to L. camara invasion. Wild elephants do not eat L. camara, and this invasive plant appears to take the place of an important food source. My results indicate that managers should prioritize their focus on certain habitats to control the impact of L. camara on elephants and vegetation. However, this study was of a correlational nature based on observational data. Experimental work is therefore needed to test for causal relationships among the variables I measured, over multiple seasons and in different habitats. Experimental evidence will enhance our understanding of how invasive weeds modify floral communities, elephant habitat use and behaviour and help determine whether L. camara is a 'passenger' or 'driver' of these changes in this ecosystem.</p>

Erosion of tropical bird diversity over a century is influenced by abundance, diet and subtle climatic tolerances

Human alteration of landscapes leads to attrition of biodiversity. Recommendations for maximizing retention of species richness typically focus on protection and preservation of large habitat patches. Despite a century of protection from human disturbance, 27% of the 228 bird species initially detected on Barro Colorado Island (BCI), Panama, a large hilltop forest fragment isolated by waters of Gatun Lake, are now absent. Lost species were more likely to be initially uncommon and terrestrial insectivores. Analyses of the regional avifauna, exhaustively inventoried and mapped across 24 subregions, identified strong geographical discontinuities in species distributions associated with a steep transisthmian rainfall gradient. Having lost mostly species preferring humid forests, the BCI species assemblage continues to shift from one originally typical of wetter forests toward one now resembling bird communities in drier forests. Even when habitat remnants are large and protected for 100 years, altered habitat characteristics resulting from isolation produce non-random loss of species linked with their commonness, dietary preferences and subtle climatic sensitivities.

State of Satiation Partially Regulates the Dynamics of Vertical Migration

Vertical migrations into shallower waters at night are beneficial for migrators as they reduce predation risk and allow migrators to encounter a higher density of prey. Nevertheless, ocean acoustics data and trawl data have shown that a portion of some vertically migrating populations remain at depth and do not migrate. One hypothesis for this phenomenon is the Hunger-Satiation hypothesis, which in part states that the non-migrating portion of the migrating species-assemblage refrains from migrating if they have full or partially full stomachs from daytime or nocturnal feeding. However, stomach fullness of the non-migrating subpopulation compared to the migrating portion has rarely been studied, due to the difficulty in obtaining sufficient samples. The stomach fullness levels of numerically abundant crustacean and fish species with well-known depth distributions were quantified in the present study. Animals were captured during night trawls from discrete-depth intervals between 0 and 1,500 m. Stomach fullness indices were assigned from 0 to 5 and compared between migratory taxa caught in shallow and deep waters. Data from the crustaceansAcanthephyra purpurea, Gardinerosergia splendens, Plesionika richardi, andSystellaspsis debilis, as well as the fishesLampanyctus alatus, Lepidophanes guentheri, andNotolychnus valdiviae, provided support for the Hunger-Satiation hypothesis, while data from the crustaceansGennadas capensisandGennadas valensand the fishBenthosema suborbitaledid not. These findings suggest that stomach vacancy may be just one of several factors regulating the dynamics of vertical migration in those species whose behavioral plasticity suggests daily “choices” in whether or not to vertically migrate.