Changes In Interspecific Competition Research Articles

The Influence of the Interaction between Climate and Competition on the Distributional Limits of European Shrews.

Simple SummaryIt is known that species’ distributions are influenced by several ecological factors. Nonetheless, the geographical scale upon which the influence of these factors is perceived is largely undefined. We assessed the importance of competition in regulating the distributional limits of species at large geographical scales. We studied European Soricidae shrews, because their species have similar diets, and focused on how interspecific competition changes along climatic gradients. We used presence data for the seven most widespread terrestrial species of Soricidae in Europe, gathered from online repositories, European museums, and gridded climate data. Using two different methods, we analysed the correlations between species’ presences, aiming to understand the distinct roles of climate and competition in shaping species’ distributions. Our results support three key conclusions: (i) climate alone does not explain all species’ distributions at large scales; (ii) negative interactions, such as competition, seem to play a strong role in defining species’ range limits, even at large scales; and (iii) the impact of competition on a species’ distribution varies along a climatic gradient, becoming stronger at the climatic extremes. Our conclusions support previous research, highlighting the importance of considering biotic interactions when studying species’ distributions, regardless of geographical scale.It is known that species’ distributions are influenced by several ecological factors. Nonetheless, the geographical scale upon which the influence of these factors is perceived is largely undefined. We assessed the importance of competition in regulating the distributional limits of species at large geographical scales. We focus on species with similar diets, the European Soricidae shrews, and how interspecific competition changes along climatic gradients. We used presence data for the seven most widespread terrestrial species of Soricidae in Europe, gathered from GBIF, European museums, and climate data from WorldClim. We made use of two Joint Species Distribution Models to analyse the correlations between species’ presences, aiming to understand the distinct roles of climate and competition in shaping species’ distributions. Our results support three key conclusions: (i) climate alone does not explain all species’ distributions at large scales; (ii) negative interactions, such as competition, seem to play a strong role in defining species’ range limits, even at large scales; and (iii) the impact of competition on a species’ distribution varies along a climatic gradient, becoming stronger at the climatic extremes. Our conclusions support previous research, highlighting the importance of considering biotic interactions when studying species’ distributions, regardless of geographical scale.

Interspecific competition changes nutrient : nutrient ratios of weeds and maize

AbstractThe elemental ratios of plant tissues are associated with the adaptive and competitive success of a plant species in an ecosystem. So far, no study has evaluated if and how crop–weed competition influences the elemental ratios of competing populations, although such information is important to understand weed infestation dynamics and to improve weed management in agroecosystems. The objective of this study was to analyze weed–crop elemental ratios during interspecific competition between weeds and crops in greenhouse experiments. For this, maize (Zea mays L.) and the weeds Amaranthus viridis L, Bidens pilosa L., and Ipomoea grandifolia (Dammer) O'Donell were grown under seven treatments: maize and weed monocultures, and maize in competition with weeds. Competition between plants practically did not influence growth and nutrient contents of maize but reduced weed growth and nutrient uptake. Maize showed few changes in elemental ratios. In contrast, B. pilosa and I. grandifolia were very sensitive to competition and showed significant increases in C : N, C : P, C : K, N : P, and N : K ratios when grown with maize. A. viridis showed low flexibility of nutrient : nutrient ratios under the same competitive pressure as that faced by B. pilosa and I. grandifolia. The interspecific competition led to increases only in the C : P ratio of A. viridis shoots. Therefore, interspecific competition changes the elemental ratios, mainly of the weeds, and the magnitude of this change is dependent on the plant species involved. Interspecific competition changes plant biomass quality (higher C : nutrient ratios), mainly for B. pilosa and I. grandifolia.

Biogeographic differences between native and non-native populations of crayfish alter species coexistence and trophic interactions in mesocosms

Biogeographical comparisons of native and non-native populations allow researchers to understand the degree to which traits contributing to invasion success are intrinsic or change during the invasion process. Here, we investigate whether traits underlying interspecific competition change following invasion and whether these alter the impacts of two crayfish congeners that have invaded into each other’s native ranges. Specifically, we compared native and non-native populations of rusty (Faxonius rusticus) and virile crayfish (F. virilis). We compared native and non-native populations of each species using laboratory assays to examine aggression and large mesocosms with the congeners in sympatry to examine growth and survival as well as impacts on lower trophic levels. We found that non-native virile crayfish were more aggressive in response to a threat than native virile crayfish and exhibited greater growth and survival in sympatry with rusty crayfish. These intraspecific differences were large enough to alter coexistence between species in the mesocosm experiment, which is consistent with patterns of coexistence between these species in the field. We did not observe differences in traits between native and non-native rusty crayfish, but rusty crayfish were consistently competitively dominant over virile crayfish in paired laboratory assays. Non-native populations of both species had greater impacts on lower trophic levels than native populations. Taken together, these findings provide new evidence that trait changes during invasions may enhance ecological impacts of invasive animals and their ability to compete with closely related native species.

Interspecific competition changes photosynthetic and oxidative stress response of barley and barnyard grass to elevated CO2 and temperature

This work focuses on the investigation of competition interaction between C3 crop barley (Hordeum vulgare L.) and C4 weed barnyard grass (Echinochloa crus-galli L.) at 2 times higher than ambient [CO2] and +4 0C higher ambient temperature climate conditions. It was hypothesized that interspecific competition will change the response of the investigated plants to increased [CO2] and temperature. The obtained results showed that in the current climate conditions, a higher biomass and photosynthetic rate and a lower antioxidant activity were detected for barley grown under interspecific competition effect. While in the warmed climate and under competition conditions opposite results were detected: a higher water use efficiency, a higher photosynthetic performance, a lower dissipated energy flux and a lower antioxidant enzymes activity were detected for barnyard grass plants. This study highlights that in the future climate conditions, barnyard grass will become more efficient in performance of the photosynthetic apparatus and it will suffer from lower oxidative stress caused by interspecific competition as compared to barley.

High competition between ant species at intermediate temperatures

Living organisms have been moving rapidly toward their favorable thermal regions as climate warms. Their competitive interactions will change significantly as a result of changes in distribution, abundance, and species composition. This study examines the relationship of competition intensity (frequency of competitive interactions) with temperature and the influence of competition on the occurrence of ant species. Competition between ants was surveyed at six different temperature sites using baits and the abundance of ants was surveyed using pitfall traps. The intensity of interspecific competition (abundance-corrected bait species displacement) was high at intermediate temperature sites (unimodal). Ant species are hierarchically organized in behavioral dominance. Two low-temperature ant species had decreased in the rank of behavioral dominance at warmer temperature sites because of the abundance of dominant intermediate temperature ant species. Ant species co-occurred randomly at the local scale. However, they were segregated at regional scale because of environmental filtering (temperature). Ant competition did not influence the occurrence of ant species at local or regional scale. These results suggest that the influence of changes in interspecific competition because of climate warming might not be great for ants in temperate regions.

Climatic turning point for beech and oak under climate change in Central Europe

The growth behavior of coexisting tree species under climate change is important from an ecological, silvicultural and economic perspective. While many previous studies are concerned with climatic limits for species occurrence, we focus on climate related shifts in interspecific competition. A landmark for these changes in competition is the ‘climatic turning point' (CTP): those climate conditions under which a rank reversal between key tree species occurs. Here, we used a common type of temperate mixed forest in Central Europe with European beech (Fagus sylvaticaL.) and sessile oak (Quercus petraea(Matt.) Liebl.) to explore the CTP under a future climate projection of increasing temperature and aridity. We selected a dry region where the prerequisite of differential climate sensitivity in mixed beech‐oak forests was fulfilled: In‐situ dendrochronological analyses demonstrated that the currently more competitive beech was more drought sensitive than sessile oak. We then used two complementary forest growth models, namely SILVA and LandClim, to investigate the climate induced rank‐reversal in species dominance and to quantify it as the CTP from beech to oak by simulating future forest development from the WETTREG 2010 A1B climate projection. Utilizing two models allowed us to draw conclusions robust against the assumptions of a particular model. Both models projected a CTP at a mean annual temperature of 11–12°C (July temperature >18°C) and a precipitation sum of 500–530 mm. However, the change in tree species composition can exhibit a time‐lag of several decades depending on past stand development and current stand structure. We conclude that the climatic turning point is a simple yet effective reference measure to study climate related changes in interspecific competition, and confirm the importance of competition sensitivity in climate change modeling.

Intra and interspecific competition among invasive and native species during early stages of plant growth

Plant competition is a primary ecological process limiting grassland restoration success. Appropriate restoration techniques require an understanding of the degree to which intra and interspecific competition control invasive and native plant growth. The objective of this study was to determine how the intensity of intra and interspecific competition changes during early stages of plant growth. Two invasive (Bromustectorum and Taeniatherum caput-medusae) and two native (Pseudoroegneriaspicata and Poasecunda) species were grown in a diallel competition experiment, either alone or in 1:1 binary combinations and exposed to two levels of N (no N or 400 mg N kg−1 soil added) in a greenhouse. Total biomass for each species was quantified over four harvests and competitive effects were calculated. Our results show that the relative magnitude of intra and interspecific competition changes through time. Intraspecific competition was intense for native species at the initial harvests and therefore important in contributing to the outcome of final size of native species seedlings. Interestingly, bluebunch wheatgrass imposed interspecific competition on annual grasses at the first two harvests and appeared to be a better competitor than Sandberg’s bluegrass. We found that fast growing invasive species became more competitive compared to slow growing native species with increasing N and appear to establish a positive feedback mechanism between size and resource uptake. Opportunities to improve restoration success exist from determining the optimum combination of density, species proportion, and their spatial arrangement in various ecosystems and environments.

Reduced horn size in two wild trophy‐hunted species of Caprinae

AbstractFactors affecting horn size in wild Caprinae are of biological and socio‐economic interest because several species are selectively harvested on the basis of this heritable character. We analysed temporal trends in horn size in two mountain ungulates from south‐eastern Spain, the Iberian wild goat Capra pyrenaica and the aoudad Ammotragus lervia. Trophy harvest is the main way in which these two species are exploited, although ‘poor‐quality’ aoudads are also selectively removed. In recent years, both populations have suffered drastic decreases in number due to outbreaks of sarcoptic mange that led to the suspension of hunting for several years. Horn length in harvested male wild goats and aoudads declined during our study period. Over an 18‐year period, the mean age of male goats shot as trophies rose by four years, while the age of trophy‐harvested aoudads decreased by around six months over a 9‐year period. Age and environmental conditions during the first few years of life explained 20% of variance in horn size in Iberian wild goat and 53% in aoudad. Population density early in life explained much of the reduction in goat horn size over time. Nevertheless, the major fall in population densities after the sarcoptic mange outbreaks did not lead to a recovery in horn size in either species. We suggest that the selective removal of large‐horned animals may contribute to a decline in horn size. Other factors that may also explain the observed pattern include changes in interspecific competition, long‐lasting maternal effects and reduced carrying capacity due to overgrazing during high density periods. Unfortunately, our data sets did not allow us to account for the possible effects of these factors.

Testing for allelopathic effects in plant competition: does activated carbon disrupt plant symbioses?

Activated carbon (AC) is widely used in ecological studies to elucidate the role of allelopathic substances in interspecific plant competition. However, by adsorbing chemical signalling compounds AC may also have negative effects on plants with symbiosis partners such as arbuscular mycorrhizal fungi and rhizobia. Here we test whether addition of AC has detrimental effects on the mycorrhizal root colonization of the native forb Plantago lanceolata and the exotic legume Lupinus polyphyllus, the nodulation of L. polyphyllus, and the nutrient uptake and growth of the plants growing in intra- and interspecific competition. Allelopathic effects probably occurred in the germination and seedling establishment phase when P. lanceolata suffered from the presence of L. polyphyllus. However, this negative effect of L. polyphyllus on P. lanceolata was not ameliorated by AC addition. AC negatively affected L. polyphyllus root biomass in week 4, and root and shoot biomass of P. lanceolata in week 9 of the experiment; both effects were independent of the presence and absence of the competing plant species. Mycorrhizal root colonization of both plant species was reduced in the presence of AC, although the effect tended to be stronger for L. polyphyllus. No significant effect of AC on the nodulation of L. polyphyllus was detected. P. lanceolata was the superior competitor and led to reduced biomasses of L. polyphyllus in interspecific competition. We conclude that AC can reduce the mycorrhization and performance of plants which may lead to changes in interspecific competition without the involvement of allelopathy. Contrary to former studies the AC used in our study did not enhance the nutrient availability for the plants, but reduced plant growth and mycorrhization. We suggest that the nutrient properties of the used AC are of crucial importance for the direction and the mechanisms of the effects and should always be reported.

Interspecific competition changes reproductive output but does not increase reproductive costs in a grassland perennial

Abstract In plants, it is hypothesized that allocation trade-offs may appear only when expenditures like seed production are high or external resources are scarce. In this study, we tested whether reproductive costs are more pronounced under enhanced interspecific competition. In a common garden, we investigated phenotypic correlations between sexual reproduction, clonal growth and storage structures in the grassland perennial, Succisa pratensis . During the past 50 years, habitats of this species have faced an expansion of clonal grasses that increase competition intensity. We simulated this process by growing five populations of Succisa from high- and low-production habitats with its clipped and non-clipped competitor, Agrostis capillaris . In addition, we experimentally removed flower heads of Succisa plants from one population grown with and without A. capillaris . We demonstrated costs of sexual reproduction by flower-head removal (resulting in increased plant size and relative allocation to belowground structures) but not by phenotypic correlations. We found no evidence that reproductive costs increase in a competitive environment and the opposite pattern was shown in both approaches used. However, high competition intensity reduced relative investment to flower-head production. In plants from low-production habitats, competition also reduced the absolute number of flower heads and belowground biomass as a result of smaller plant size. We assume that populations from low-production habitats are more prone to extinction as they have a reduced likelihood of local persistence and of escape to more suitable habitats during advancing succession.

The arctic fox Alopex lagopus in Fennoscandia: a victim of human-induced changes in interspecific competition and predation?

After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid 1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations.

Breeding suppression in the bank vole as antipredatory adaptation in a predictable environment

In northern Fennoscandia, microtine rodent populations fluctuate cyclically. The environment of an individual vole can be considered to be predictable when the risks of predation and intra- and interspecific competition change with the cycle, such that both are high during the population highs of voles. The risk of predation is also high during the vole crash. After the crash, the vole population is characterized by low intra- and interspecific competition and low predation pressure. The main predators affecting voles during the crash are the small mustelids, least weasel and stoat. The density of these specialist predators declines drastically during the winter after the vole crash. We studied experimentally the impact of the perceived presence of stoats on the breeding and mating behaviour of voles. In a series of breeding experiments with bank voles,Clethrionomys glareolus, both old and young females suppressed breeding when exposed to the odour of stoats,Mustela erminea. The weights of females decreased in both experimental and control groups, but more among the voles under odour exposition. It seems that females actively avoided copulations under high predation risk and that breeding suppression is mediated by a change in female mating behaviour. There was no change in male behaviour or physical condition between the experimental and control treatments. An alternative mechanism for the observed breeding suppression could be the one caused by decreased feeding in females mediated with low energy intake which does not allow breeding. Regardless of its mechanism, delay of breeding should increase the probability of non-breeding females to survive to the next breeding season. The females surviving the crash should gain a strong selective advantage in a predator-free environment of the subsequent breeding season, which could explain the adaptive function of this antipredatory strategy.