Browsing by Subject "predator-prey interactions"
Now showing items 1-2 of 2
-
(2022)Populations of forest grouse – capercaillie (Tetrao urogallus), black grouse (Lyurus tetrix) and hazel grouse (Tetrastes bonasia) - have been declining through all of Europe. Habitat loss, fragmentation and degradation are recognized to be the most important ultimate causes behind this trend. In Fennoscandia, there is a general consensus that forestry practices have a primary role, even though the mechanisms are still not fully understood. Nest predation is generally thought to be an important proximate cause of the declines, but how nest predation relates to habitat changes remains poorly understood. I combined long-term data provided by the Natural Resources Institute Finland (LUKE) from inventory studies, both for grouses and predators, with an artificial nest experiment. I investigated a) how predation rate varies with forest age and landscape structure; b) what is the possible role of non-native mesopredator species as predators; c) how nest predation rate relates to larger scale reproductive success. In spring 2021, I placed 141 nests with two hen eggs each, in the regions of Kainuu and North Karelia for 14 days with camera traps. The nests were equally divided between mature forests (>80 years), young forests (<40 years) and edges of mature forests (in a mature forest 5m from a clearcut or a field). I found that the overall predation rate was low (~13 %) and similar in the three sites, but predation time was faster in mature forests, suggesting that when these are scarce, they can act as an ecological trap by increasing nest detectability. However, nest predation decreased with the increasing of mature forests in the landscape around the nest, supporting the hypothesis that on a larger scale forestry may increase generalist predator densities. Areas with higher predator densities suffered higher nest losses. The main predators were pine martens, badgers and magpies, followed by bears and ravens. No nests were predated by raccoon dogs or American minks. There was no correlation between areas with higher nest predation and areas where grouse had lower reproductive success which may result from other factors, e.g., chick predation. My results add to the diverse outcomes of several studies of grouse nest predation in Europe, which together indicate large variation in nest predation, no consistency in predatory species, and weak effects of landscape composition on nest predation.
-
(2024)As a result of habitat degradation, prey depletion, and human-wildlife conflict, African lion (Panther leo) population has been decreasing rapidly in the past decades. Via top-down regulation, lions maintain trophic balance by controlling herbivore populations, and consequently affecting vegetation. Due to their important role in ecosystems, reintroducing lions to small, fenced reserves has become an increasingly important tool in biodiversity conservation and ecosystem restoration, especially in South Africa. However, introducing lions into small systems can negatively affect prey populations as well as smaller carnivores if lion populations are not actively managed, and these impacts can vary depending on prey selection of introduced lions. Prey selection of lions provide valuable information for managers, but currently the knowledge of the impacts of population management on the diet of lions is very limited. Therefore, with this study I was aiming to investigate the influence of sex and management interventions, such as lion removals and introductions, and group size control on the prey preferences of lions in a small, fenced reserve. The study was conducted by using long-term data from the past 30 years on the lion population in the Munywana Conservancy in South Africa. In particular, I used the data on lions’ diet and their history (including management interventions and group sizes), and data on prey abundances. First, I used Jacob’s index to determine prey preferences and specific prey selection of Munywana’s lions in general, per lion unit per year, as well as per sex and lion unit size. Eight main prey species (nyala, warthog, giraffe, wildebeest, impala, kudu, zebra, buffalo) of lions in Munywana were considered in this study. To evaluate the influence of management interventions, group size, and sex on the prey preferences of lions, I used generalized linear mixed models with zero-inflated beta-regression at the level of whole Munywana and at the level of lion unit. Lastly, I used chi-square test to evaluate the impact of lion origin by comparing the diets of introduced and native lions, and to determine whether population management has longer term impacts on prey selection by comparing within lion unit variation in prey selection across years. It was observed that lions are not opportunistic feeders, and they had overall strong prey preferences: some prey species were fed upon more often than others regardless of the abundance of the available prey species. The most preferred prey species in Munywana were warthog and wildebeest, followed by giraffe and zebra, while impala, nyala, and buffalo were generally avoided. The results of this study showed that lion management interventions and lion origin have independent impacts on prey preferences even when sex and group size were accounted for. Introduction of new lions resulted in higher preference for wildebeest and zebra, and lower preference for warthog and nyala, while introduced lions preferred kudu, giraffe, buffalo, and wildebeest significantly more compared to native lions. Sex and group size also had an impact on prey selection: the preference for zebra increased as group size increased, and male lions preferred giraffe, warthog and nyala more compared to female lions, and the removal of male lions resulted in decreased preference for zebra and giraffe. The results of my study supported hypotheses that lion management interventions, lion origin, group size, and sex have an impact on prey selection, but the most significant factors differed between prey species. In addition, the interaction between management interventions, and sex, and their impact on population characteristics of lions appeared to be extremely important, but due to limitations in the data, the relationship between lion translocations, changes in group compositions, and their results in prey choices could not be assessed in a required detail, highlighting the importance for further investigations. My findings reflect the importance of taking prey selection of the apex predator into consideration when planning management interventions and reintroduction projects since it has a potential to substantially alter prey populations, and indirectly vegetation. However, prey selection is a complex process consisting of several factors and their interactions, and therefore further research would be required to enhance our understanding of this process. Management of lion populations is essential in small, fenced reserves, and wider understanding of the impacts of management interventions on the prey preferences would allow conservationists to create better management plans and ensure effective predator conservation as well as the long-term sustainability of predator-prey systems.
Now showing items 1-2 of 2