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Title:Effects of fragmentation and invasion on ant communities
Author(s):Achury Morales, Rafael Andres
Director of Research:Suarez, Andrew V.
Doctoral Committee Chair(s):Suarez, Andrew V.
Doctoral Committee Member(s):Berenbaum, May R.; Harmon-Threatt, Alexandra; Allan, Brian F.
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Neotropical ant-fauna
indicator species
tropical forest
habitat fragmentation
beta diversity
Wasmannia auropunctata
interspecific competition
Neotropical dry forests
resource partitioning
co-occurrence patterns
discovery-dominance trade-offs
numerical dominance
biological invasions
long-term dynamics
Argentine ant
native communities
habitat loss and fragmentation
Linepithema humile
ant abundance
ecological impacts
southern California
Abstract:Human alteration of natural environments has triggered a sixth major extinction event. Activities such as land-use change, habitat loss and fragmentation, the transport and establishment of invasive species, overhunting, pollution and climate change have threatened tens of thousands of species worldwide. Moreover, these factors do not act independently and synergies among them often occur. For example, climate change and habitat fragmentation might promote the range expansion of invasive species, which in turn reduces diversity in remaining habitat. Despite the fact that habitat loss and biological invaders have been widely studied and received special attention due to a strong association between them, the relative contribution of each to biodiversity loss has not always been clear. Habitat fragmentation is a consequence of habitat destruction when continuous areas of natural habitats are divided into small, isolated fragments, and has detrimental consequences for the maintenance of biodiversity. Fragmentation can reduce habitats to a size that is too small to support viable populations, and also, force species into a metapopulation structure. Additionally, habitat fragmentation creates large amounts of degraded “edge” habitat generating difficult conditions for the survival of many species. These small and isolated populations can be subjected to species loss in fragmented landscapes as a result of stochastic and deterministic processes. Environmental, demographic and genetic stochasticity can arise because the remaining habitat may contain only a subset of the original fauna. Deterministic processes are also prominent when modifications occur at the landscape-level for example, increased edge and isolation, decreased fragment size, and degradation in the quality of the habitat. These landscape characteristics are especially problematic in tropical ecosystems where nutrient-poor soils do not easily meet the agricultural demands of growing human populations. A consequence of replacing tropical forests with agriculture is the creation of landscapes consisting of fragments of natural vegetation surrounded by a matrix of low-diversity land uses such as pastures, sugarcane and oil palm plantations. The resulting remnants generally maintain lower species diversity relative to unfragmented forest, and the species composition of what remains often includes generalist and invasive species. Another causative agent of extinction are introduced species, which have significant effects on biodiversity by directly competing with, preying upon, parasitizing, or otherwise indirectly affecting native populations. Successful invaders are often habitat generalists making them more likely to colonize habitats that are more susceptible to invasion, including simplified or species-poor communities, fragmented or edge habitats, and habitats with new niche opportunities generated by disturbance. To conserve biodiversity and minimize the negative consequences of habitat loss and invasion, it is a priority to measure how richness and species composition change in fragmented landscapes, and identify the mechanisms that drive biodiversity loss. To address those issues, I focused on ants due to their ecological dominance, sensitivity to habitat transformation and disturbance, and their success as invaders. Ants, with 16 subfamilies and almost 14,000 species, are distributed globally and stand out for their dominance in biomass among terrestrial environments. Most ants are omnivorous, but many are specialized predators or form obligate mutualisms with plants. Additionally, ants can be separated into guilds that occupy different strata (e.g., canopy, litter, hypogeics), and are relatively easily sampled for long-term monitoring and inventories. Their taxonomy and basic ecology is well described and they are often used as indicator species. In general, ant assemblages respond to habitat transformation with changes in community composition and loss of species richness, which in turn can lead to changes in competitive interactions, facilitating the invasion of introduced species. The general objective of my dissertation was to investigate the effects of habitat loss and fragmentation, and invasion on natural communities, and to identify mechanisms that promote changes in ant assemblages. To achieve these objectives, I first reviewed the literature evaluating the impacts of habitat fragmentation on ants in the tropical dry forest in Colombia (Chapter 1). Tropical dry forest ecosystems are threatened worldwide, but in Colombia they are critically endangered due to a variety of human activities, including logging, mining and the conversion of forest into agriculture and pasture for livestock. There are already comprehensive reviews evaluating the impacts of habitat fragmentation on native communities generally and for ants in particular. Consequently, I narrowed my literature search to this ecosystem and country because of the lack of information for this species-rich biogeographic region. In Colombia, tropical dry forests are located in three areas and there is little published information on their ant fauna. I used this research to identify detrimental effects on species richness and abundance of several ant species due to factors such as habitat loss, increased edge, and landscape context surrounding the forests. Conversely, some dominant ants increased in abundance and benefited from these same factors. Based on the available information, I highlighted research and management opportunities for this ecosystem that will potentially benefit the conservation and restoration of the ant fauna and the ecosystem services they provide. In Chapter 2, I examined whether changes in land use lead to modifications in richness and composition of ant species communities in tropical rain forests. Throughout the tropics, there have been cumulative losses of lowland forests over many decades, and studies evaluating the responses of habitat destruction have been focused on vertebrates, while insects are generally neglected by such surveys. By sampling landscape elements with different levels of disturbance in previously unexplored areas of tropical rain forest in Colombia, I demonstrated that ant richness decreased in landscape elements with higher disturbance levels (e.g., pastures and gallery forests). Moreover, a loss of structural complexity has the greatest effect on ant communities, with forest type habitats harboring more unique species that scored higher conservation values. I reported 11 new ant records for the Colombian inter-Andean region and two new records for the country (Mycocepurus curvispinosus and Rhopalothrix isthmica), showing that conservation even of small forest remnants is important due to their ability to retain high arthropod diversity in tropical landscapes.  Despite being a topic of contention, interspecific competition is considered a hallmark of ant ecology, and understanding the role of this interaction in the structure and dynamics of biological communities has been a longstanding goal of ecologists. I investigated whether habitat disturbance due to anthropogenic transformation modifies the outcome of competitive interactions, by examining a different set of predictions in relation to the structure of ant assemblages in a highly modified landscape in the Neotropics (Chapter 3). I described results based on ants collected using tuna fish baits, where forests with lower level of disturbance exhibited segregated patterns of co-occurrence compared to forests with higher disturbance and disassembled communities (i.e., random co-occurrence). A segregated community is assumed to be structured by competition. Furthermore, the lower the disturbance level, the more species had the opportunity to coexist at baits, and these had lower levels of monopolization by dominant ants (e.g., Wasmannia auropunctata, a global introduced species). Finally, I identified mechanisms of coexistence based on trade-offs of competitive abilities; most of the species showed a trade-off between discovery of the bait and domination of the bait, whereas the little fire ant (W. auropunctata) was able to be proficient at both, thus braking the trade-off that promotes coexistence. I discuss the importance of understanding interspecific interactions and associated factors that modify their outcome, especially in the context of disturbance and competitively dominant ants. In Chapter 4, I evaluated the long-term effects of habitat fragmentation and its interaction with invasive species on native epigeic ant communities. There are two contrasting hypotheses regarding the impacts of invasive species over time. First, impacts are initially high just after the introduction, but native populations have the capacity to adapt and subsequently the impacts will be reduced after evolution of the recipient community. Second, even after long periods of time, introduced species maintained an overall high impact on the native community with no changes through time. I used a well-structured survey carried out 21 years ago and resurveyed ants in fragments located in southern coastal California, to determine whether there is evidence of changes in the impact of the Argentine ant (Linepithema humile) in this area with time. I revisited each of the 40 fragments sampled previously and found that the abundance of this invader has increased while the native ant community has not rebounded to preinvasion levels, which supports the hypothesis of persistent effects over time. Nonetheless, habitat loss and fragmentation also are pervasive and interact with the ongoing invasion by promoting further decline in richness of native ants and local extinctions (e.g., army ants in the genus Neivamyrmex). In conclusion, I observed that invaders with high numerical dominance, in conjunction with high levels of perturbation, can maintain long-term invasion effects on native communities without apparent changes.
Issue Date:2019-04-17
Rights Information:Copyright 2019 Rafael Achury Morales
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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