Effects of territorial damselfish on an algal-dominated coastal coral reef

Territorial damselfish are important herbivores on coral reefs because they can occupy a large proportion of the substratum and modify the benthic community to promote the cover of food algae. However, on coastal coral reefs damselfish occupy habitats that are often dominated by unpalatable macroalgae. The aim of this study was to examine whether damselfish can maintain distinctive algal assemblages on a coastal reef that is seasonally dominated by Sargassum (Magnetic Island, Great Barrier Reef). Here, three abundant species (Pomacentrus tripunctatus, P. wardi and Stegastes apicalis) occupied up to 60% of the reef substrata. All three species promoted the abundance of food algae in their territories. The magnitudes of the effects varied among reef zones, but patterns were relatively stable over time. Damselfish appear to readily co-exist with large unpalatable macroalgae as they can use it as a substratum for promoting the growth of palatable epiphytes. Damselfish territories represent patches of increased epiphyte load on macroalgae, decreased sediment cover, and enhanced cover of palatable algal turf.     

Effects of territorial intrusions on eavesdropping neighbors: communication networks in nightingales

Animal communication often occurs in communication networksin which multiple signalers and receivers are within signalingrange of each other. In such networks, individuals can obtaininformation on the quality and motivation of territorial neighborsby eavesdropping on their signaling interactions. In songbirds,extracting information from interactions involving neighborsis thought to be an important factor in the evolution of strategiesof territory defense. In a playback experiment with radio-taggednightingales Luscinia megarhynchos we here demonstrate thatterritorial males use their familiar neighbors' performancein a vocal interaction with an unfamiliar intruder as a standardfor their own response. Males were attracted by a vocal interactionbetween their neighbor and a simulated stranger and intrudedinto the neighbor's territory. The more intensely the neighborhad interacted with playback, the earlier the intrusions weremade, indicating that males eavesdropped on the vocal contestinvolving a neighbor. However, males never intruded when wehad simulated by a second playback that the intruder had retreatedand sang outside the neighbor's territory. These results suggestthat territorial males use their neighbors' singing behavioras an early warning system when territorial integrity is threatened.Simultaneous responses by neighboring males towards unfamiliarrivals are likely to be beneficial to the individuals in maintainingterritorial integrity.     

Effects of environmental variation on extinction and establishment

Theoretical models predict that increasing environmental variation increases the probability of extinction, decreases the probability of establishment, and influences the distribution of times to extinction or establishment. We conducted an experiment with 281 independent populations of Daphnia magna under controlled laboratory conditions to test these predictions. Consistent with the theory, the fraction of populations going extinct increased and the fraction of populations establishing self‐sustaining populations decreased under higher levels of environmental variation compared with controls. Time to extinction decreased under higher levels of environmental variation, but we found no effect on time to establishment. These results are consistent with theoretical predictions from models of extinction. They therefore support the use of stochastic population models to predict the fates of introductions of non‐indigenous species or native endangered species based on historic fluctuations and/or expected future conditions.     

Effects of territorial damselfish on cryptic bioeroding organisms on dead Acropora formosa

Many damselfishes exclude other grazers from their territories and “farm” filamentous algae within their territories. In this study the indirect effect of damselfish territories on faunal composition and abundance of internal bioeroders of dead Acropora formosa (Dana, 1846) was investigated in territories of two damselfish species, Stegastes nigricans (Lacepède, 1802) and Plectroglyphidodon lacrymatus (Quoy and Gaimard, 1825). S. nigricans tends to be more protective and defend their territories more aggressively than P. lacrymatus. Newly killed branches of A. formosa were placed inside and outside damselfish territories, for 1 or 2 years, at a coral reef near Zanzibar, Tanzania. As predicted, the coral branches became covered with more filamentous algae in the S. nigricans territories than in the controls, with intermediate levels in the P. lacrymatus territories. Among the internal bioeroding fauna, polychaetes were by far the most common group. In total, there were significantly more borers in the first year than the second, which was mainly due to a high abundance of sabellids. Furthermore, sabellids were significantly more abundant in control areas and in the P. lacrymatus territories compared to the S. nigricans territories. However, many other genera showed the opposite pattern, with more polychaetes in the fish territories compared to the controls. There was also a clear difference in assemblage structure between S. nigricans territories and controls. Thus, we found strong effects of whether a piece of coral was placed inside or outside a damselfish territory on the abundance of many of the bioeroding taxa. We discuss multiple reasons for these indirect effects of the territories, including that deposit feeding bioeroders may benefit from the dense algal turf found inside the territories whereas suspension feeding bioeroders may benefit from substrate with less filamentous algae found outside territories. Considering our results in the context of the large areas of coral reefs that typically are defended as territories by damselfishes, these fish are likely to have a considerable impact on the boring community of a coral reef.     

Effects of exposure to predatory cues on territorial behaviour of male fathead minnows

We conducted a laboratory study to determine if male fathead minnows, Pimephales promelas, altered their territorial behaviour associated with reproduction in response to combinations of visual and chemical cues from northern pike, Esox lucius. We introduced the following stimuli to a territorial male: a brick (control), fathead minnow alarm pheromone, a pike fed brook stickleback, Culea inconstans, or a pike fed fathead minnow. The territorial behaviour of males did not change when the control was added. Male minnows experiencing threat from pike fed stickleback significantly reduced the frequency at which they performed three territorial behaviours, but, within 12 h, had returned to pre-exposure activity levels. Male minnows subjected to alarm pheromone alone and to pike fed fathead minnow significantly reduced their territorial behaviour, abandoned their nests, and did not return to pre-exposure levels of activity after 24 h. We suggest that because risk of predation triggers prolonged decreases in territorial defense, it may affect competition between nesting males and female mate choice. We conclude that fathead minnows can assess the severity of predatory threat and adjust their reproductive behaviour accordingly.     

Effects of tunnel structures of two termite species on territorial competition and territory size

The foraging territories of 2 subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), were simulated using a model to explore how territorial intraspecific competition changes with 4 variables characterizing the formation of territory: the number of primary tunnels, N₀; the branching probability, P_branch; the number of territories, N; and the blocking probability, P_block. The blocking probability P_block quantitatively describes the probability that a tunnel will be terminated when another tunnel is encountered; higher P_block values indicate more likely termination. Higher tunnel-tunnel encounters led to denser tunnel networks. We defined a territory as a convex polygon containing a tunnel pattern and explored the effects of competition among termite colonies on territory size distribution at steady state attained after sufficient simulation time. At the beginning of the simulation, N = 10, 20,…, 100 initial territory seeds were randomly distributed within a square area. In our previous study, we introduced an interference coefficient γ to characterize territorial competition. Higher γ values imply higher limitations on network growth. We theoretically derived γ as a function of P_block and N. In this study, we considered the constants in γ as functions of N₀ and P_branch so as to quantitatively examine the effect of tunnel structure on territorial competition. By applying statistical regression to the simulation data, we determined the generalized γ functions for both species. Under competitive conditions, territory size is most strongly affected by N₀, while the outcome of territorial competition is most strongly affected by N, followed by P_block and N₀.     

Effects of corticosterone on territorial behavior of free-living male song sparrows Melospiza melodia

A group of 10 territorial male song sparrows, Melospiza melodia, were given subcutaneous implants of corticosterone in Silastic tubing. A second group of 10 territorial males were given empty implants as controls. After 18-24 hr all males were then subjected to a simulated territorial intrusion (STI) by placing a caged male song sparrow in the center of the subject's territory, and playing tape recorded songs through a speaker placed alongside. Significantly fewer males with corticosterone implants responded to STI than to controls, and the latency to respond was longer. Of the 3 experimental males that did respond to STI, all had a lower frequency of songs and did not approach the simulated intruder as closely as controls. Many males were captured 2-7 days after implantation and blood samples collected for measurement of circulating hormone levels. As expected, plasma levels of corticosterone were high in the group given corticosterone implants. However, plasma levels of luteinizing hormone (LH) were not affected by treatment with corticosterone, and although circulating levels of testosterone were depressed slightly compared with controls, they were within the normal range for territorial and breeding males. There were no differences in body mass despite greatly increased fat depots in males treated with corticosterone. These data suggest that high levels of corticosterone, similar to those measured during stressful episodes both in the laboratory and field, may suppress territorial behavior independently of the adenohypophysial-gonad axis. Since plasma levels of LH and testosterone are not depressed markedly, thus maintaining the gonads in a near functional state, renesting can begin as soon as environmental conditions ameliorate. Such mechanisms could potentially increase the probability of raising viable young after unpredictable, severe weather resulted in failure of the previous breeding attempt.     

Effects of extreme temperature on seedling establishment of nonnative invasive plants

Climate change and plant invasion are two of the most important ecological issues facing the world today. Extreme events are likely to play an important role in plant invasion. For example, tolerance to temperature stress is critical for plant germination and survival of seedlings. Nonnative invasive species tend to differ from co-occurring native species in several traits. Increased mean temperatures are known to enhance the risk of plant invasions, but few experimental studies have linked plant invasion to both increasing mean temperature and extreme (low and high) temperatures. Ten plant species from Asteraceae (six nonnative invasive and four native species) were chosen and six temperatures (extremely low, average winter, average annual, average summer, high and extremely high) were used to test the effects of extreme temperatures on plant invasion in southern China. The results showed that nonnative invasive plant species (IS) germinated more readily and the seedlings grew better than those of native plant species (NS) at high temperatures, suggesting that global warming may facilitate invasion. Extreme temperatures decreased the seed germination rate and seedling growth of both IS and NS, although NS were more tolerant of extremely low temperatures (5/0 °C). IS, in turn, were more tolerant of extremely high temperatures (40/35 °C). Extreme high temperatures may increase the risk of plant invasion because IS seedlings are better able to become established, whereas low temperatures may hinder invasion. In addition, the species-specific differences in plant origin (IS and NS) and temperature tolerance were correlated with other climatic factors and should be considered in managing invasive species in a changing world.     

Effects of restoration strategies on vegetation establishment in retired cranberry bogs

Plant Ecology - The wetlands of the New Jersey Pine Barrens (USA) have historically been utilized for large-scale cranberry (Vaccinium macrocarpon) farming. In 2003, 3800 hectares of retired...     

Effects of increasing temperature on social behaviour in territorial groups of pumpkinseed sunfish,Lepomis gibbosus

To study the effect of thermal stress on their social behaviour, ten territorial groups of pumpkinseed sunfish, Lepomis gibbosus, were subjected to a 1°C temperature increase every other day until they succumbed. Social behaviour remained remarkably unchanged by thermal stress until nearly lethal levels. As temperature rose, ritualised behaviours increased in frequency, then fell off, probably reflecting changes in general activity.Behavioural and physiological signs of stress appeared from 31 to 38°C. Events during these social breakdowns are described and compared with the response of two other freshwater fishes with different social organisations subjected to the same thermal regime.     

Effects of territorial intrusions, courtship feedings and mate fidelity on the copulation behaviour of the osprey

We studied copulation behaviour of the osprey, Pandion haliaetus, a semicolonial, fish-eating raptor, in Corsica (Mediterranean). Pairs copulated over a long period (45 days) and at a high rate, with, on average, 288 within-pair copulations (WPCs) for a clutch. Pairs breeding at higher density faced more frequent territorial intrusions than others and were potentially at an increased cuckoldry risk. However, and contrary to predictions of the ‘paternity assurance’ hypothesis for frequent copulations, we found that WPC rate decreased with increasing frequency of territorial intrusions. Male territory attendance increased with territorial intrusion frequency, to the detriment of the food provisioning of the female. Both attempted and successful WPC rates were positively related to the amount of food delivered by the male. Thus, the more frequent the territorial intrusions, the more time the male spent within his territory, the less he courtship fed and the smaller the fish he delivered, and the less the pair copulated successfully. WPC rate was also higher in newly formed pairs than in established pairs, and decreased with increasing pair bond length. The results suggest that males rely on mate guarding rather than frequent copulations to ensure paternity, and do not support the idea that sperm competition is the main cause of frequent WPCs. Nonfertilization functions of frequent copulations, such as pair bonding, mate assessment and mate retention, were likely early in the prelaying period. The findings that WPC rate decreased with mate fidelity and that females traded copulations for food suggest that mate retention was a possible function of frequent copulations in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Historical landmarks of autophagy research

The year of 2013 marked the 50th anniversary of C de Duve''s coining of the term “autophagy” for the degradation process of cytoplasmic constituents in the lysosome/vacuole. This year we regretfully lost this great scientist, who contributed much during the early years of research to the field of autophagy. Soon after the discovery of lysosomes by de Duve, electron microscopy revealed autophagy as a means of delivering intracellular components to the lysosome. For a long time after the discovery of autophagy, studies failed to yield any significant advances at a molecular level in our understanding of this fundamental pathway of degradation. The first breakthrough was made in the early 1990s, as autophagy was discovered in yeast subjected to starvation by microscopic observation. Next, a genetic effort to address the poorly understood problem of autophagy led to the discovery of many autophagy-defective mutants. Subsequent identification of autophagy-related genes in yeast revealed unique sets of molecules involved in membrane dynamics during autophagy. ATG homologs were subsequently found in various organisms, indicating that the fundamental mechanism of autophagy is well conserved among eukaryotes. These findings brought revolutionary changes to research in this field. For instance, the last 10 years have seen remarkable progress in our understanding of autophagy, not only in terms of the molecular mechanisms of autophagy, but also with regard to its broad physiological roles and relevance to health and disease. Now our knowledge of autophagy is dramatically expanding day by day. Here, the historical landmarks underpinning the explosion of autophagy research are described with a particular focus on the contribution of yeast as a model organism.     

Effects of residence time on displays during territory establishment in a lizard

We know little about how signals are used during territory establishment, particularly when potential competitors are separated by distances that are typical of those between neighbours. I studied the effects of residence time on the display behaviour of male Anolis sagrei lizards in long- and short-distance contexts. In the long-distance context, the habitat patches of two male lizards were 5 m apart, separating the males by a distance typical of that in territorial neighbourhoods. For the short-distance context, I placed two males in one habitat patch. In both contexts, either 1-day residents were paired with new arrivals, or both individuals were new arrivals. In the long-distance contexts only, I also created situations in which both individuals were 1-day residents. Residence time affected the relative frequencies of headbob displays ('bobbing displays' and 'nodding displays'). However, the direction of the effect depended on opponent proximity. In long-distance contexts, 1-day residents performed fewer bobbing displays relative to nodding displays than did new arrivals; in short-distance contexts 1-day residents performed more bobbing displays relative to nodding displays than did new arrivals. The results suggest that signalling during territory establishment is governed by a qualitatively different set of rules when potential competitors are at short versus long distances. Copyright 2000 The Association for the Study of Animal Behaviour.     

Effects of vegetation canopy and climate on seedling establishment in Mediterranean shrubland

Abstract. Question: Does the influence of plant canopy on seedling establishment interact with climate conditions, and particularly, do intensified drought conditions, enhance a positive effect of the vegetation canopy on seedlings in Mediterranean‐type ecosystems. Location: Mediterranean shrubland near Barcelona, Spain at 210 m a.s.l. Methods: Over the course of four years we recorded seedling emergence and survival in open areas and below vegetation under control, drier and warmer experimental climatic conditions. Results: Seedling emergence is more sensitive to climate conditions than later stages of growth. When considering the whole set of species, the total number of established seedlings at the end of the experiment was lower in the drought and warming stands than in control ones, and vegetation canopy increased the number of these seedlings in the drought stands. Drought reduced seedling emergence but not warming, while the interaction between climate treatments and vegetation canopy was not significant. Seedling survival was lower in the warming treatment than in the control. Under drought conditions, vegetation canopy increased seedling emergence of the dominant Globularia alypum. In control stands, vegetation canopy reduced their survival. Vegetation canopy increased the survival of the dominant Erica multiflora in warming stands, and it reduced the survival of G alypum in drought stands. No significant effects of drought and warming were observed in the seed rain of these two species. Conclusions: The balance of the facilitation‐competition interactions between vegetation canopy and seedling establishment in Mediterranean‐type ecosystems determined by water availability, and drought conditions enhance the positive effect of vegetation canopy. This interaction is species‐specific and shows important between‐year variability.