Biocrusts and the ecosystem services they provide are becoming more susceptible to fire as exotic annual grass invasions facilitate the spread of desert wildfires. Further, precipitation patterns across the western United States are predicted to change over the next century, and have the potential to dramatically influence fire regimes and the recovery of burned biocrusts. Despite these changes to desert fire and precipitation cycles, our understanding of post-fire biocrust recovery is limited, especially regarding the first two years after fire. To investigate biocrust recovery, we created burn manipulations (i.e., unburned and burned) and tracked crust form and function over two years in one cold and one hot desert ecosystem (UT, USA). We evaluated the entire bacterial community, but focused on Cyanobacteria species that confer soil stability and N fixation capabilities to biocrusts. Specifically, we quantified shifts in biocrust bacterial community composition using target metagenomics of 16S rDNA; monitored biocrust moss and lichen cover; measured N fixation potential; and assessed soil infiltration rates and soil stability. We found little evidence that biocrust form or function recovered from fire within two years. Based on pyrosequencing results, fire altered biocrust community composition in interspace and shrub biocrusts. Cyanobacteria species were almost completely eliminated by fire, constituting 9-21% of unburned plots and less than 0.01% of burned interspace and shrub biocrust communities. Based on cover estimates, no lichen or moss species survived the fire or recovered within two years. N fixation potentials decreased by at least six-fold in burned interspace biocrusts, representing a reduction in soil N inputs into already N-limited desert soils. Soil infiltration rates also drastically declined in burned biocrusts and remained depressed, but only remained depressed for one year. To investigate the interactions between biocrust recovery, fire, and precipitation, we nested precipitation treatments manipulating the amount of monthly rainfall (i.e., ambient, plus 30% and minus 30%) within burn treatments during the second year. Soil NH4+ was the only parameter to be affected by precipitation, and exhibited a positive relationship with precipitation magnitude at the end of one year. Our results demonstrate that fire is a strong destabilizer of the bacterial components of biocrust communities and that the ecosystem services provided by crusts recover at different rates, with N dynamics recovering more slowly than soil ecohydrology.

No description available.

No description available.

No description available.

Le lac Tonle Sap (TSL) est l'un des plus grands lacs du monde et est connu comme un hot-spot de la biodiversité en Asie du Sud-Est. En raison de la grande diversité ainsi que de la productivité élevée de poissons, le lac contribue à un apport important en protéines pour la population cambodgienne. Cette étude vise principalement à étudier (1) la dynamique spatiale et temporelle de la composition des communautés de poissons, (2) les effets des facteurs environnementaux sur la distribution des espèces et (3) l'effet de l'abolition des lots de pêche sur la biomasse, les communautés de poissions et le structure des poissons. En utilisant des méthodes statistiques multivariées sur les données de poissons et de variables environnementales, je suis en mesure de mettre en évidence les principales conclusions suivantes: * Les communautés de poissons du TSL étaient composées de deux assemblages de poissons: l'assemblage du nord, principalement caractérisé par des poissons noirs, et l'assemblage du sud, principalement lié aux poissons blancs, gris et estuariens. Les assemblages de poissons de la période 1994-1995 étaient représentés par l'abondance de tous les groupes fonctionnels, c'est-à-dire les poissons noirs, blancs et gris, et pour la période de 1996 à 1999, les assemblages étaient liés aux poissons blancs et gris. * Les distributions des abondances espèces de poissons n'étaient pas homogènes dans le TSL. De plus, les aires de distributions des espèces étaient différentes et étaient régies par des combinaisons distinctes de caractéristiques de l'habitat et de facteurs climatiques. * H. lobatus et H. siamensis peuvent coexister ensemble, mais la synchronisation et la migration de H. lobatus conduisent toujours à celles de H. siamensis. Ces résultats suggèrent que la population de H. lobatus est plus sensible aux variations d'impulsion de flux que celles de H. siamensis. Ceci indique que les variations des impulsions d'écoulement sont les principaux déterminants responsables de la dynamique temporelle de chaque espèce.[...] / Tonle Sap Lake (TSL) is one of the world's largest lakes and is a biodiversity hotspot in Southeast Asia. It supports high fish productivity which sustains protein supply for millions of people in the region. This study aims to investigate (1) spatial and temporal dynamics of fish community composition, (2) the effects of environmental factors on fish distribution and (3) effects of fishing lot abolishment on fish biomass, community and structure in TSL. By using multivariate statistical methods on fish and environmental data, the thesis highlights that: * There were two fish assemblages in TSL: the northern assemblage, mostly characterised by black fishes, and the southern assemblage, mainly linked to white, grey and estuarine fishes. Fish assemblages from earlier years (1994 and 1995) were represented by the abundances of all functional groups, i.e. black, white and grey fishes, and from 1996 to 1999, the assemblages were linked only to white and grey fishes. * Fish species distributions were not homogeneous within TSL. In addition, species distribution areas were different and were governed by distinct combinations of the local habitat characteristics and regional climatic factors. * H. lobatus and H. siamensis can co-occur together, but synchronisation and migration of H. lobatus always lead those of H. siamensis. These results suggest that the population of H. lobatus is more responsive to flow pulse variations than those of H. siamensis.[...]

Rain forest canopies are renowned for their very high biodiversity and the critical role they play in key ecological processes and their influence on global climate. Despite that New Zealand supports one of the most diverse and extensive epiphyte flora of any temperate forest system, few studies have investigated epiphyte communities and their invertebrate fauna along with factors that influence their distribution and composition. This thesis represents the first comprehensive study of entire epiphyte communities and their resident invertebrate fauna in the canopy of New Zealand’s indigenous forests. The aim of this study was to determine spatial patterns of epiphyte and invertebrate species richness, abundance and community composition in relation to abiotic variables, and in particular, the responses of these communities to elevated temperature and rainfall. This study was carried out in coastal lowland podocarp-broadleaved forests at two sites on the West Coast of the South Island of New Zealand. Samples from 120 mat-forming epiphyte assemblages located on inner canopy branches of 40 northern rata (Metrosideros robusta) trees were studied to characterise the component flora and fauna. Additionally, biomass, branch and tree characteristics and community responses to treatments designed to elevate temperature and rainfall to simulate predicted climate change were measured. This investigation revealed astonishing diversity and functional complexity of epiphyte and invertebrate life in this ecosystem. The 30.6 kg (dry weight) of epiphyte material collected contained a total of 567 species, 170 epiphyte and 397 invertebrate (excluding immature specimens and mites) species, including at least 10 species new to science and many undescribed species Epiphyte communities were found to be dominated by non-vascular plants (80 % of the total species richness), particularly liverworts and invertebrate communities were dominated with respect to abundance (~ 80 % of the total individuals) by Acari, Collembola and Hymenoptera (primarily ants) and functionally by scavengers and ants. Epiphyte and invertebrate communities were highly variable with respect to spatial patterning of species richness, abundance and composition across sites, among trees within sites and among branches within trees. Overall, a highly significant proportion, > 75 %, of the variance could be attributed to differences at the branch level, but these differences could not be explained by the environmental factors measured. There were no consistent relationships between the spatial pattern of epiphytes and invertebrates, or between vascular and non-vascular plants. However, there were significant positive correlations between epiphyte biomass and invertebrate species richness (r = 0.472; p < 0.0001) and abundance (r = -0.395; p < 0.0001), as well as non-living epiphyte biomass and scavenger species richness (r = 0.4; p < 0.0001). Microclimatic measurements taken on epiphyte mats were also highly variable with respect to temperature and relative humidity at similar physical locations within the same tree as well as across trees within sites. There was also considerable variation in the intensity and frequency of climatic extremes, although potentially harmful climatic conditions were experienced by all the epiphyte mats for which weather variables were measured. Negative correlations existed between both epiphyte and invertebrate community composition and increased temperatures expressed as cumulative degree days above 5˚C. However, variability was such that there was no direct evidence that increased temperature and rainfall treatments had an effect on invertebrate species richness, abundance or diversity. Northern rata host trees harbour an astonishingly diverse and complex canopy flora and fauna that is characterised by high spatial variability. Such variability highlights that to determine species distribution and community dynamics in canopy habitats in response to disturbance caused either by climate change or invasive species the structure of entire communities at different taxonomic and spatial scales, along with their responses to microclimatic factors, need to be studied. If such complexities are not taken into account, inappropriate interpretation may result in poor decisions concerning the conservation status, vulnerability and subsequent management of such unique ecosystems.

Landnutzungsänderungen, Habitatverlust und Fragmentierung gehören zu den Hauptursachen des weltweiten Biodiversitätsrückgangs. In Mitteleuropa zählen Kalkmagerrasen zu den artenreichsten Lebensräumen. Sie weisen eine hohe Vielfalt an xero- und thermophilen Pflanzen- und Invertebratenarten auf, sind jedoch zunehmend durch landwirtschaftliche Intensivierung und Nutzungsaufgabe gefährdet. Sie sind auf Beweidung und Mahd angewiesen, was jedoch für die Landwirte heutzutage unwirtschaftlich geworden ist. Daher finden sich zunehmend kleine Fragmente innerhalb einer für die meisten der spezialisierten Magerrasenarten ungeeigneten, von intensiver Landwirtschaft geprägten Umgebung. Der erste Teil dieser Arbeit untersucht den Einfluss der Fragmentgröße, der Habitatkonnektivität, der Zusammensetzung der umgebenden Landschaft und der Pflanzenartenzahl auf die Zusammensetzung der Zikadengemeinschaft. Zikaden sind eine überaus artenreiche Gruppe phytophager Insekten mit enger Bindung an die Vegetationsstruktur und -zusammensetzung. In der Umgebung von Göttingen wählten wir 14 große (>1 ha) und 14 kleine (<1 ha) Kalkmagerrasenflächen entlang von Gradienten zunehmender Konnektivität mit anderen Magerrasenflächen, zunehmender Pflanzenartenzahl und zunehmender Landschaftskomplexität, d.h. dem Prozentsatz Ackerfläche innerhalb eines 500 m-Radius, aus. Zunehmende Isolation verringerte die Zikadenartenzahl in einfachen (von Feldern geprägten), jedoch nicht in komplexen Landschaften. Dieser Effekt wurde von den Generalisten getrieben. Die Artenzahl der Generalisten nahm auf kleinen Fragmenten mit zunehmender Konnektivität zu, wogegen sie auf großen Flächen unverändert blieb. Weiterhin nahm die Artenzahl der Generalisten mit steigender Pflanzenartenzahl auf vernetzten Magerrasen stärker zu als auf unvernetzten. Unsere Ergebnisse zeigen, dass die Insektenartenvielfalt auf Kalkmagerrasenfragmenten nicht nur durch Konnektivität allein geprägt wird, sondern vielmehr von einem Zusammenspiel aus Konnektivität, Landschaftszusammensetzung und Pflanzenartenzahl bestimmt wird. Im zweiten Teil dieser Arbeit verfolgen wir das Ziel, zur Lösung der sogenannten SLOSS-Debatte (“Single Large Or Several Small”) beizutragen, in der diskutiert wird, ob es besser ist, wenige große oder mehrere kleine Fragmente eines Habitattyps zu erhalten. Man nimmt an, dass kleine Fragmente aufgrund der größeren abgedeckten geographischen Distanzen eine größere Heterogenität und dadurch eine höhere Gesamtartenzahl aufweisen. Dagegen weisen große Fragmente stabilere Lebensraumbedingungen und größere Populationen auf. Neben Zikaden und Pflanzen wurden auch Daten zu Wanzen und 114 Schnecken aufgenommen. Sowohl die Gesamtartenzahl aller vier Taxa als auch die Zahl der Spezialisten war auf mehreren kleinen Fragmenten wesentlich höher als auf einem oder zwei großen Fragmenten gleicher Gesamtgröße. Jedoch war die Artenzusammensetzung auf großen und kleinen Fragmenten unterschiedlich und einige der seltensten Spezialisten waren an große Flächen gebunden. Hingegen spielte die Zusammensetzung der umgebenden Landschaft keine wichtige Rolle für Artenzahl und -zusammensetzung. Diese Ergebnisse stellen den Fokus auf entweder große oder kleine Habitatfragmente infrage. Für einen erfolgreichen Biodiversitätserhalt ist daher der Schutz sowohl großer als auch kleiner Habitatfragmente zwingend notwendig. Im dritten Teil dieser Arbeit untersuchen wir den Einfluss der Bewirtschaftungsart (Beweidung, Mahd, Nutzungsaufgabe), der Landschaftszusammensetzung und Konnektivität auf die Artenzahl, Artenzusammensetzung und merkmalsbasierte Reaktionen (Körpergröße und Rote Liste-Status) von neun Taxa: Pflanzen, Schmetterlinge, Bienen, Heuschrecken, Schwebfliegen, Spinnen, Wanzen, Kurzflügler und Zikaden. Wir wählten 30 kleine Kalkmagerrasenfragmente (<1 ha) entlang von unabhängigen Konnektivitäts- und Landschaftskomplexitätsgradienten aus. Ein zunehmender Prozentsatz an Ackerfläche in der Umgebung der Fragmente führte zu einem Verlust von 29 % der Gesamtartenzahl. Wir nehmen an, dass Landschaften, die von Ackerfläche dominiert werden, weniger Alternativhabitat und Nahrungsressourcen bieten, was zu einer verringerten Artenzahl führt. Habitatkonnektivität erhöhte im Allgemeinen die Artenzahl. Dieser Effekt war bei den großen, vermutlich ausbreitungsfähigeren Arten eines Taxons stärker ausgeprägt als bei den kleinen Arten. Beweidung hatte einen deutlich negativeren Einfluss auf die Artenzahl als Mahd (einmal jährlich) oder kurzzeitige Nutzungsaufgabe (5-15 Jahre). Der Grund dafür könnte der durch Beweidung verursachte größere Schaden und die Entnahme der Nahrungsressourcen phytophager Insekten sein. Zudem führte jeder der drei Bewirtschaftungsweisen zu einer unterschiedlichen Artenzusammensetzung aller Taxa. Daher sollte die bevorzugte Bewirtschaftungsoption kleiner Kalkmagerrasenfragmente ein Wechsel zwischen Mahd und kurzzeitiger Nutzungsaufgabe in Kombination mit einer Diversifizierung der umgebenden Landschaft sein. Zusammenfassend lässt sich sagen, dass die allgemein verbreitete Konzentration auf große Habitatfragmente überdacht werden sollte, da der Schutz sowohl kleiner als auch großer Fragmente unerlässlich ist. Bei der Planung von Schutzmaßnahmen für fragmentierte Offenlandlebensräume sind lokale Einflüsse wie Fragmentgröße und Bewirtschaftung zwar wichtig, aber nicht ausreichend: Landschaftsfaktoren wie Habitatkonnektivität und Landschaftszusammensetzung müssen ebenfalls in die Schutzbemühungen mit einbezogen werden um das langfristige Überleben von spezialisierten Pflanzen- und Invertebratenarten zu sichern.

Rain forest canopies are renowned for their very high biodiversity and the critical role they play in key ecological processes and their influence on global climate. Despite that New Zealand supports one of the most diverse and extensive epiphyte flora of any temperate forest system, few studies have investigated epiphyte communities and their invertebrate fauna along with factors that influence their distribution and composition. This thesis represents the first comprehensive study of entire epiphyte communities and their resident invertebrate fauna in the canopy of New Zealand’s indigenous forests. The aim of this study was to determine spatial patterns of epiphyte and invertebrate species richness, abundance and community composition in relation to abiotic variables, and in particular, the responses of these communities to elevated temperature and rainfall. This study was carried out in coastal lowland podocarp-broadleaved forests at two sites on the West Coast of the South Island of New Zealand. Samples from 120 mat-forming epiphyte assemblages located on inner canopy branches of 40 northern rata (Metrosideros robusta) trees were studied to characterise the component flora and fauna. Additionally, biomass, branch and tree characteristics and community responses to treatments designed to elevate temperature and rainfall to simulate predicted climate change were measured. This investigation revealed astonishing diversity and functional complexity of epiphyte and invertebrate life in this ecosystem. The 30.6 kg (dry weight) of epiphyte material collected contained a total of 567 species, 170 epiphyte and 397 invertebrate (excluding immature specimens and mites) species, including at least 10 species new to science and many undescribed species Epiphyte communities were found to be dominated by non-vascular plants (80 % of the total species richness), particularly liverworts and invertebrate communities were dominated with respect to abundance (~ 80 % of the total individuals) by Acari, Collembola and Hymenoptera (primarily ants) and functionally by scavengers and ants. Epiphyte and invertebrate communities were highly variable with respect to spatial patterning of species richness, abundance and composition across sites, among trees within sites and among branches within trees. Overall, a highly significant proportion, > 75 %, of the variance could be attributed to differences at the branch level, but these differences could not be explained by the environmental factors measured. There were no consistent relationships between the spatial pattern of epiphytes and invertebrates, or between vascular and non-vascular plants. However, there were significant positive correlations between epiphyte biomass and invertebrate species richness (r = 0.472; p < 0.0001) and abundance (r = -0.395; p < 0.0001), as well as non-living epiphyte biomass and scavenger species richness (r = 0.4; p < 0.0001). Microclimatic measurements taken on epiphyte mats were also highly variable with respect to temperature and relative humidity at similar physical locations within the same tree as well as across trees within sites. There was also considerable variation in the intensity and frequency of climatic extremes, although potentially harmful climatic conditions were experienced by all the epiphyte mats for which weather variables were measured. Negative correlations existed between both epiphyte and invertebrate community composition and increased temperatures expressed as cumulative degree days above 5˚C. However, variability was such that there was no direct evidence that increased temperature and rainfall treatments had an effect on invertebrate species richness, abundance or diversity. Northern rata host trees harbour an astonishingly diverse and complex canopy flora and fauna that is characterised by high spatial variability. Such variability highlights that to determine species distribution and community dynamics in canopy habitats in response to disturbance caused either by climate change or invasive species the structure of entire communities at different taxonomic and spatial scales, along with their responses to microclimatic factors, need to be studied. If such complexities are not taken into account, inappropriate interpretation may result in poor decisions concerning the conservation status, vulnerability and subsequent management of such unique ecosystems.

Biological invasions are reportedly one of the major contributory factors to biodiversity loss worldwide. The impacts of invasive alien plant (IAP) species on native communities are widely documented in the scientific literature, however, there is still a lack of detailed information on their impacts within the most vulnerable habitats. Riparian habitats are highly dynamic systems and naturally disturbed, making them particularly vulnerable to invasion. Climate change, directly or indirectly, is also predicted to adversely impact river systems, which may subsequently alter invasion rates and the impacts of IAPs. However, the interactions between climate and IAPs and their combined effects on vegetation have rarely been examined. To address these knowledge gaps, this thesis investigates: (1) the role of environmental variables, such as sediment loading or climate-related changes to river flow regime, on the abundance of IAPs within riparian zones; (2) how variation in IAP abundance impacts native vegetation, relative to the effects of native dominant plant species and (3) some of the mechanisms underlying the effects of IAPs in riparian habitats. Historic and recent field survey data were used to investigate changes in riparian vegetation on British rivers during the last 20 years. Analyses indicate that IAPs had a negative but small effect on native plant diversity. Overall, changes in land use and differences in flow regime between recording periods were the most important predictors of plant community change. Specifically, IAPs had a greater probability of being present along lowland rivers that experienced increased frequency of high flow events. On a local scale across rivers in Scotland, the abundance of IAPs was constrained by greater soil moisture in summer, whilst greater abundance was associated with tree-lined banks. Both native dominant species and IAPs negatively affected subordinate species abundance to a greater extent than species richness, although this effect varied spatially with bank elevation. Artificial turf mats were used to quantify viable propagules within riverine sediment deposited over-winter along invaded riverbanks. The data indicate that there is a legacy effect of IAP abundance, with the most invaded sites being associated with higher sediment loading the following year, though, contrary to the general pattern, 12 sediment associated propagules were scarcer at invaded sites. Moreover, lower above-ground native diversity was associated with sites which had been previously invaded. Plant species composition in the propagule bank and above-ground vegetation were highly dissimilar, particularly closest to the water’s edge at highly invaded sites. This suggests that mono-specific stands of IAPs proliferate best under less disturbed environmental conditions, although fluvial disturbance events may be required to create opportunities for initial establishment. The propagule bank contributed very little to the above-ground vegetation, nor did it limit invasion, suggesting that above-ground plant composition is largely dictated by competitive interactions. The findings presented in this thesis suggest that invasion by IAPs is an additional stressor for native vegetation within riparian habitats, modifying above-ground plant communities via competition and suppressing recruitment from the propagule bank. However, native dominant species common in riparian habitats also negatively impact, subordinate species via competition, in some cases equalling the effect of IAPs. Native dominant and IAP species are differently affected by environmental factors operating in the riparian zone, which may provide future opportunities for reducing and managing invasions.

Abstract Describing how and why species composition of ecological communities varies across spatial and temporal scales is a primary objective for ecological research. A key challenge is to distinguish changes in community composition resulting from external factors from the natural background variability. In this thesis I aimed to study: 1) the level of temporal variation in community composition of stream macroinvertebrates, 2) the role of different environmental factors to temporal variability, 3) the effect of temporal variability on bioassessment outcomes, and 4) comparability of different approaches to study community variability through time. A majority of the studied macroinvertebrate communities showed lower level of inter-annual variation, i.e. temporal turnover, than expected by chance. The observation of high community stability was further supported by the low level of inter-annual variation in taxonomic completeness (quotient of observed and expected number of species, O/E). Despite the low absolute variation in O/E, ecological status assessments varied annually. Thus the use of one year data may bias management decisions. Macroinvertebrate communities experienced similar dynamics across several spatial extents, from riffles within a stream to streams among regions, suggesting that large-scale extrinsic factors are the major driver of community dynamics. Especially climatically exceptional years may have a strong imprint on community variability. However, at the within-stream scale, coherence was lower than expected, indicating that community dynamics may be driven by different processes at different spatial extents. Stream macroinvertebrate community dynamics were strongly related to in-stream vegetation, temporal variability decreasing with increasing macrophyte cover. Importantly, the effect of in-stream vegetation on temporal turnover of macroinvertebrate communities was masked by the stochastic effect of habitat connectivity, suggesting that unless stochastic effects are controlled for, the role of deterministic processes may be obscured, thus affecting our ability to understand and predict community changes through time. In addition, different approaches to study temporal variability may disagree on estimates for the level of temporal turnover and factors explaining it – a fact that should be taken into account when planning and comparing studies. / Tiivistelmä Yksi ekologisen tutkimuksen keskeisistä tavoitteista on kuvata, miten ja miksi eliöyhteisöjen koostumus muuttuu paikasta ja ajankohdasta toiseen. On tärkeää pystyä erottamaan erilaisten ulkoisten tekijöiden aiheuttamat muutokset luonnollisesta taustavaihtelusta. Väitöskirjani tavoitteena oli selvittää 1) miten paljon virtavesien pohjaeläinyhteisöissä tapahtuu ajallista vaihtelua 2) mitkä ympäristötekijät vaikuttavat yhteisöjen ajalliseen vaihteluun 3) miten ajallinen vaihtelu vaikuttaa ympäristön tilan arviointiin ja 4) kuinka vertailukelpoisia ovat eri lähestymistavat ajallista vaihtelua tutkittaessa. Valtaosa tutkituista pohjaeläinyhteisöistä vaihteli vuosien välillä vähemmän kuin olisi sattumalta odotettavissa osoittaen varsin suurta ajallista pysyvyyttä. Käsitystä yhteisöjen pysyvyydestä tuki myös vähäinen vuosittainen vaihtelu ekologista tilaa kuvaavassa taksonomisessa eheydessä (=havaitun ja odotetun lajiston suhde O/E). Huolimatta näennäisen pienestä vaihtelusta O/E suhteessa paikkakohtaiset tilaluokka-arviot saattoivat vaihtua vuodesta toiseen. Yhden vuoden aineistoon perustuvat tilan arvioinnit voivat siis johtaa virheellisiin johtopäätöksiin. Pohjaeläinyhteisöjen ajallinen vaihtelu oli samankaltaista eri mittakaavoilla niin peräkkäisten koskipaikkojen kuin eri alueilla sijaitsevien purojen välillä. Suuren mittakaavan ympäristötekijät näyttävät siis säätelevän eliöyhteisöjen ajallista vaihtelua. Erityisesti ilmastotekijöiltään poikkeukselliset vuodet säätelevät eliöyhteisöjä, ja niiden vaikutus voi näkyä vielä useiden vuosien kuluttua. Vaihtelun samankaltaisuus peräkkäisten koskipaikkojen välillä oli kuitenkin odotettua pienempää. Yhteisöjä voivat siis säädellä osittain eri tekijät eri mittakaavoilla. Tutkittujen pohjaeläinyhteisöjen ajallisen vaihtelun voimakkuus liittyi erityisesti vesikasvillisuuden määrään: vaihtelu väheni kasvillisuuden lisääntyessä. Kasvillisuuden määrän vaikutus peittyi kuitenkin satunnaisten tekijöiden alle. Jos satunnaisia tekijöitä ei huomioida, deterministiset syy-seuraussuhteet voivat jäädä huomaamatta heikentäen mahdollisuuksiamme ymmärtää ja ennustaa eliöyhteisöjen vaihtelua. Lisäksi eri lähestymistavat ajallista vaihtelua tutkittaessa voivat johtaa erilaisiin arvioihin vaihtelun suuruudesta ja siihen vaikuttavista tekijöistä, mikä tulisi ottaa huomioon tutkimuksia suunnitellessa ja niiden tuloksia vertailtaessa.