Division of Labor Associated with Brood Rearing in the Honey Bee: How Does It Translate to Colony Fitness?

Division of labor is a striking feature observed in honey bees and many other social insects. Division of labor has been claimed to benefit fitness. In honey bees, the adult work force may be viewed as divided between non-foraging hive bees that rear brood and maintain the nest, and foragers that collect food outside the nest. Honey bee brood pheromone is a larval pheromone that serves as an excellent empirical tool to manipulate foraging behaviors and thus division of labor in the honey bee. Here we use two different doses of brood pheromone to alter the foraging stimulus environment, thus changing demographics of colony division of labor, to demonstrate how division of labor associated with brood rearing affects colony growth rate. We examine the effects of these different doses of brood pheromone on individual foraging ontogeny and specialization, colony level foraging behavior, and individual glandular protein synthesis. Low brood pheromone treatment colonies exhibited significantly higher foraging population, decreased age of first foraging and greater foraging effort, resulting in greater colony growth compared to other treatments. This study demonstrates how division of labor associated with brood rearing affects honey bee colony growth rate, a token of fitness.     

The role of queen mandibular pheromone and colony congestion in honey bee (Apis mellifera L.) reproductive swarming (Hymenoptera: Apidae)

The roles of honey bee queen mandibular pheromone and colony congestion in the inhibition of swarming were investigated. Two colony siz.es were used: small, congested colonies and large, uncongested colonies. Both groups of colonies were treated with various dosages of the five-component, synthetic queen mandibular pheromone in the spring, and the extent and timing of swarming were followed. Most treatment groups received pheromone or a solvent blank (control) on a stationary slide; one group of the congested colonies received a pheromone treatment via an aerosol spray. The pheromone was not effective at delaying swarming in the congested colonies at any dosage applied on slides, but the aerosol spray-treated colonies swarmed significantly later in the season than the control colonies. The uncongested, pheromone-treated colonies exhibited a dose-dependent delay in swarming, with the highest dosage colonies swarming almost four weeks later than the control colonies. These results indicate an interaction between congestion and pheromone in the control of honey bee reproduction. While congestion may in itself be a factor stimulating swarming, these results are consistent with the interpretation that colony congestion reduces the transmission of queen pheromone within the nest, thereby removing the queen 's pheromone-based inhibition of queen rearing and subsequent swarming by workers.     

Elimination of sexual brood in the Argentine antLinepithema humile: queen effect and brood recognition

Mated queens of the antLinepithema humile (Iridomyrmex humilis Mayr) introduced into dequeened colony fragments rearing sexual brood elicited worker aggression resulting in queen larvae being bitten and eliminated. By contrast, male larvae were spared. Regarding queen brood, killing mainly concerned small and medium sized larvae. A large proportion of the large larvae escaped extermination, and prepupae and pupae were spared. These data suggest that workers were able to discriminate sex, caste and age of the brood. That a queen pheromone may be involved was shown by experiments using whole or cut corpses that were either rinsed or not rinsed in pentane. The pheromone eliciting worker aggressive behaviour was shown to act over a short distance, suggesting that it is somewhat volatile. Similarities and differences between this new queen pheromone and other known queen pheromones acting on queen production or worker attraction are discussed as well as the origin of the signals underlying the recognition of the larval classes.     

Brood development into sexual females depends on the presence of a queen but not on temperature in an ant dispersing by colony fission,Aphaenogaster senilis

Abstract. 1. In eusocial insects, colony fission is a mode of dispersal by which a young queen leaves her nest with some workers to found a new colony. In these species, adult females (workers and the queen) should allocate most resources to increasing their colony size, which constrains the possibility of fission. In contrast, developing diploid larvae should have a preference for becoming a queen and having their own offspring, rather than becoming workers and rearing the offspring of other females. 2. In the ant Aphaenogaster senilis, queens are produced in very small numbers, suggesting that adult females control larval development. We used a 6‐year series of data on more than 300 nests to determine the annual cycle of worker and queen production. Although both overlapped, the latter mostly occurred in the second half of the summer, after a major peak of worker emergence. Young queens were also often produced in nests whose reproductive queen had died, thus allowing her replacement. Overall, we estimate that only 0.07% of diploid larvae actually develop into gynes. 3. Laboratory experiments indicated that brood is bipotent until the second larval instar. Diploid larval development into queen was favoured by the removal of the mother queen, but was not affected by rearing temperature. 4. Our data suggest that most diploid broods are forced by the adults to develop into workers rather than into gynes. However, when the queen is not present due to death or after a fission event, a few larvae are allowed to develop into gynes. One way for workers to limit the development of larvae might be by controlling the amount of food they receive.     

Nest Enlargement in Leaf-Cutting Ants: Relocated Brood and Fungus Trigger the Excavation of New Chambers

During colony growth, leaf-cutting ants enlarge their nests by excavating tunnels and chambers housing their fungus gardens and brood. Workers are expected to excavate new nest chambers at locations across the soil profile that offer suitable environmental conditions for brood and fungus rearing. It is an open question whether new chambers are excavated in advance, or will emerge around brood or fungus initially relocated to a suitable site in a previously-excavated tunnel. In the laboratory, we investigated the mechanisms underlying the excavation of new nest chambers in the leaf-cutting ant Acromyrmex lundi. Specifically, we asked whether workers relocate brood and fungus to suitable nest locations, and to what extent the relocated items trigger the excavation of a nest chamber and influence its shape. When brood and fungus were exposed to unfavorable environmental conditions, either low temperatures or low humidity, both were relocated, but ants clearly preferred to relocate the brood first. Workers relocated fungus to places containing brood, demonstrating that subsequent fungus relocation spatially follows the brood deposition. In addition, more ants aggregated at sites containing brood. When presented with a choice between two otherwise identical digging sites, but one containing brood, ants'' excavation activity was higher at this site, and the shape of the excavated cavity was more rounded and chamber-like. The presence of fungus also led to the excavation of rounder shapes, with higher excavation activity at the site that also contained brood. We argue that during colony growth, workers preferentially relocate brood to suitable locations along a tunnel, and that relocated brood spatially guides fungus relocation and leads to increased digging activity around them. We suggest that nest chambers are not excavated in advance, but emerge through a self-organized process resulting from the aggregation of workers and their density-dependent digging behavior around the relocated brood and fungus.     

Movement of honey bee (Apis mellifera L.) queen mandibular gland pheromone in populous and unpopulous colonies

The mode of intranest transfer of the honey bee queen mandibular gland pheromone complex (QMP) was investigated in unpopulous and populous, slightly congested colonies, using synthetic QMP containing tritiated 9-keto-2(E)-decenoic acid, one of the QMP components. Radiolabel was rapidly transported from the center to the peripheral regions of the nest, and in a manner consistent with worker to worker transport. Population size and congestion had no effect on the relative rates of movement from the center to the periphery of the nest or on the mean amounts of radiolabel on individual bees. However, a significantly smaller proportion of the workers in the populous colonies received detectable amounts of radiolabel than in the uncongested colonies, and workers carrying especially large amounts of radiolabel were less numerous in the crowded colonies. It is suggested that, at the stage of colony development that the colonies were in, population size has more of an effect on intranest pheromone transmission than does crowding. Interference with pheromone transfer may occur only at higher levels of congestion than were created, and nearer to the reproductive phase of colony development. An alternative hypothesis is that colony crowding does not significantly affect QMP transport and that the onset of reproductive queen rearing may be associated more with changes in worker thresholds of response to QMP.     

Queen brood reared in worker cells by the social wasp,Vespula germanica (F.) (Hymenoptera: Vespidae)

Summary The rearing of queen brood from worker cells in the nests ofVespula germanica (F.) in Australia was found at all stages of the colony cycle from early summer to autumn. Worker cells used to rear queens were 17% wider at their open ends than cells used for worker production, and in all other respects their dimensions were greater. The volume of a worker cell used for queen nearing was 21% larger than cells used for rearing workers but half the volume of a normal queen cell. Queen pupae reared in worker cells were significantly smaller than those reared in queen cells of the same nest. The spatial distribution of queen pupae in worker comb tended to be random although some evidence of nonrandom clustering was noted.The significance of this phenomenon is discussed in relation to caste differentiation and queen-control of gyne initiation and production. It is concluded that the phenomenon is neither seasonal nor due to some intrinsic component of the colony's annual cycle, and that it is unlikely to be an emergency queen-rearing response. Development of queens in worker cells may have occurred during favourable feeding regimes, perhaps determined by the benign Australian environment.     

Queen pheromone regulates egg production in a termite

In social insects, resource allocation is a key factor that influences colony survival and growth. Optimal allocation to queens and brood is essential for maximum colony productivity, requiring colony members to have information on the total reproductive power in colonies. However, the mechanisms regulating egg production relative to the current labour force for brood care remain poorly known. Recently, a volatile chemical was identified as a termite queen pheromone that inhibits the differentiation of new neotenic reproductives (secondary reproductives developed from nymphs or workers) in Reticulitermes speratus. The same volatile chemical is also emitted by eggs. This queen pheromone would therefore be expected to act as an honest message of the reproductive power about queens. In this study, we examined how the queen pheromone influences the reproductive rate of queens in R. speratus. We compared the number of eggs produced by each queen between groups with and without exposure to artificial queen pheromone. Exposure to the pheromone resulted in a significant decrease in egg production in both single-queen and multiple-queen groups. This is the first report supporting the role of queen pheromones as a signal regulating colony-level egg production, using synthetically derived compounds in a termite.     

Intraspecific usurpation of incipient fire ant colonies

Brood raiding, or reciprocal stealing of brood, is common amongincipient colonies of the fire ant Solenopsis invicta. Paradoxically,workers from a colony that loses its brood during a raid oftenabandon their nest and join the winning colony. Queens abandonedby their workers may then migrate from their original nest siteand attempt to forcefully usurp another incipient colony bydisplacing that colony's queen or queens. This study examinedfactors that influence the success of usurpation attempts. Queensattempting to usurp a nearby colony after laboratory brood raidswere successful in less than 30% of trials. Usurpation attemptswere more successful if workers familiar to the migrating queenwere present in the nest, as would happen if a queen were tofind the colony to which her workers had moved. Cross-fosteringexperiments showed that this effect was due to familiarity ratherthan relatedness. Usurpation attempts were less successful ifthey were delayed by 16 h. The probability of usurpation successwas not reduced by doubling the number of defending workersin the invaded colony. However, colonies founded by three queenswere almost always able to resist usurpation attempts. Theseresults support the hypothesis that workers abandon their natalcolony after losing a brood raid to increase the likelihoodthat their queen can usurp the colony to which they migrate.These results also provide the first evidence that coloniesof ants founded by several queens are better able to resistusurpation attempts than colonies founded by a single queen     

Brood pheromone regulates foraging activity of honey bees (Hymenoptera: Apidae)

Brood pheromone modulated the foraging behavior of commercial honey bee, Apis mellifera L., colonies pollinating a 10-ha market garden of cucumber, Cucurbita pepo L., and zucchini, Cucumis saticus L., in Texas in late autumn. Six colonies were randomly selected to receive 2000 larval equivalents of brood pheromone and six received a blank control. The ratio of pollen to nonpollen foragers entering colonies was significantly greater in pheromone-treated colonies 1 h after treatment. Pheromone-treated foragers returned with pollen load weights that were significantly heavier than controls. Pollen returned by pheromone-treated foragers was 43% more likely to originate from the target crop. Number of pollen grains washed from the bodies of nonpollen foragers from pheromone-treated colonies was significantly greater than controls and the pollen was 54% more likely to originate from the target crop. Increasing the foraging stimulus environment with brood pheromone increased colony-level foraging and individual forager efforts. Brood pheromone is a promising technology for increasing the pollination activity and efficiency of commercial honey bee colonies.     

Effect of primer pheromones and pollen diet on the food producing glands of worker honey bees (Apis mellifera L.)

Cooperative brood care is highly developed in the honey bee such that workers called nurses use their hypopharyngeal and mandibular glands to biosynthesize proteinaceous secretions that are progressively provisioned to larvae. The role that honey bee primer pheromones play in the functional physiology of food producing glands was examined. The combined and separate effects of queen mandibular pheromone (QMP) and brood pheromone (BP) on amount of protein extractable from hypopharyngeal and mandibular glands of workers reared for 12 days with and without pollen diets was measured. In rearing environments with a pollen diet, BP, and QMP + BP pheromone treatments significantly increased extractable protein from both glands. Bees reared with QMP + pollen had amounts of protein extractable from both glands that were not significantly different from control bees (no pheromones, no pollen). Pollen in the diet alone significantly increased amounts of protein extractable from glands versus control. In rearing environments without pollen, QMP + BP had a synergizing effect on amount of protein in both glands. The QMP + BP treatment was the only rearing environment without a pollen diet where protein amounts were significantly greater than the control. The synergizing effect of QMP + BP on extractable mandibular and hypopharyngeal gland protein suggests a highly derived role for the combined effect of these two primer pheromones on honey bee cooperative brood care. Mandibular gland area was significantly and positively correlated with extractable protein. Amounts of extractable protein from both glands declined significantly with age of workers in all treatments. However, treatment significantly affected rate of decline. The adaptive significance of gland protein amounts in response to pheromones and pollen diet are discussed.     

Gyne development in the Argentine ant Iridomyrmex humilis: role of overwintering and queen control

Abstract A possible stimulatory effect of overwintering on gyne development in Iridomyrmex humilis (Mayr) was investigated. Although gyne-potent larvae are present in the nest throughout the year, small queenless colony fragments composed of freshly overwintered ants (collected in late winter or early spring) produced 3–8 times more gynes than comparable fragments made up of non-freshly overwintered ants (collected at other times of the year). Apparently, this stimulatory effect of overwintering acts on both the developmental potential of larvae and the tendency of workers to rear sexually competent larvae as gynes; queenless colony fragments in which either the brood or workers were freshly overwintered produced more gynes than fragments composed of non-freshly overwintered workers or brood but fewer than fragments containing both brood and workers freshly overwintered. This increased sexualization potential of larvae due to overwintering is enough to overcome weak pheromonal inhibition of queens associated with low queen number; a single queen in a large freshly overwintered colony fragment is insufficient to inhibit gyne development, whereas ten queens are totally inhibitory. In non-freshly overwintered colony fragments one queen is completely inhibitory. Variability in egg developmental potential according to queen age does not appear to play a major role in the seasonal production of gynes, because at least some eggs of very young queens (less than 3 weeks old) are capable of gyne development. In the field this stimulatory effect of overwintering is superimposed on a seasonal fluctuation in the combined strength of pheromonal queen control. In southern France, gynes are produced only in spring where they arise primarily from overwintered larvae just after a sharp drop in queen number, and presumably the total level of inhibitory queen pheromone, due to the massive execution of queens by workers.     

An alternative strategy for maintenance of eusociality after nest destruction: new nest construction in a primitively eusocial wasp

Although nests are central to colonial life in social insects, nests are sometimes damaged by predators or natural disasters. After nest destruction, individuals usually construct new nests. In this case, a sophisticated mechanism like the scent trail pheromone used in large insect colonies that recruit individuals to new nest sites would be important for the maintenance of eusociality. In independent-founding Polistes wasps, it is well known that queens enforce workers physiologically on the natal nests even if evidence of trail pheromone use has not been exhibited. We investigated the effect of the queen on an alternative strategy for the maintenance of eusociality by first females after nest destruction in the primitively eusocial wasp Polistes chinensis. We predicted that the first females in queen-absent colonies have various behavioral options after nest destruction. Even if the females construct new nests cooperatively with other individuals, the new nest construction should be conducted more smoothly in queen-present colonies because the queens regulate the behavior of wasps. We made wasps construct new nests by removing the entire brood from existing nests. The presence of the queen did not cause variation in the alternative strategy of the first females, as the first females (workers) usually constructed new nests cooperatively irrespective of the queen-presence. Thus, the workers in the queenpresent colonies affiliated to the new nest construction more smoothly and constructed new nests more efficiently than workers in the queen-absent colonies. Our results suggest that the presence of the queen is important for maintaining eusociality in primitively eusocial wasps after nest destruction. Received 8 February 2005; revised 5 October 2005; accepted 17 October 2005.     

<Emphasis Type="Italic">Polistes japonicus</Emphasis> (Hymenoptera,Vespidae) queens monopolize ovipositing but are not the most active aggressor in dominant-subordinate interactions

In order to elucidate the dominant–subordinate relationship between the foundress and workers, five colonies of the paper wasp Polistes japonicus were observed in a netted and covered cage located outdoors. The number of workers in each colony ranged from four to eight. Workers were divided into first and second broods. Abdominal wagging and ovipositing were performed almost exclusively by the foundress throughout colony development. However, an analysis of aggressive encounters indicated that although the foundress hardly received dominance behaviors (aggression) from workers, it lacked either partially or completely the following characteristics of the queen that are usually seen in paper-wasp colonies with independent-founding queens (except in one colony that produced no second brood): the queen being socially dominant over any worker (the queen had more wins than losses in one-on-one dominance contests with any worker), exhibiting the highest frequency of dominance behaviors, and directing dominance behaviors primarily toward the socially most-dominant worker. In particular, during the mixed-brood period (when all first- and second-brood workers were present on the nest) the foundress hardly exhibited dominance behaviors toward socially dominant workers (mainly second brood) but frequently directed dominance behaviors toward socially subordinate workers (mainly first brood). The foundress disappeared in two colonies before the reproductives emerged; in these colonies the socially most-dominant worker inherited the colony and laid many eggs. The frequency of abdominal wagging by these two foundresses decreased during colony development, while it did not in the other colonies. This suggests that abdominal wagging provides information about the vigor of the performer. The superseder was socially dominant over all other workers, but spent little time wagging its abdomen and allowed some workers to lay eggs.     

Brood Pheromone Modulation of Pollen Forager Turnaround Time in the Honey Bee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

Foraging for pollen is an important behavior of the honey bee because pollen is their sole source of protein. Through nurse bees, larvae are the principal consumers of pollen. Fatty acid esters extractable from the surface of larvae, called brood pheromone, release multiple colony-level and individual foraging behaviors increasing pollen intake. In this study pollen forager turnaround time was measured in observation hives supplemented with brood pheromone versus a blank control treatment. Treatment with brood pheromone significantly decreased pollen forager turnaround time in the hive between foraging bouts by approximately 72%. Concurrently, brood pheromone increased the ratio of pollen to non-pollen foragers entering colonies. Brood pheromone has been shown to release most of the mechanisms known to increase pollen intake by colonies acting as an important regulator of colony foraging decisions and growth.     

Phenotype and individual investment in cooperative foundress associations of the fire ant, Solenopsis invicta

Fire ant (Solenopsis invida) queens founding a colony with unrelatednest mates potentially face a trade-off. Increased individualinvestment enhances worker production, colony survival, andgrowth. However, increased investment may reduce a queen's probabilityof surviving fights that invariably arise after worker eclosion.Indeed, previous studies showed that queens lose less weight(a measure of investment) when initiating colonies with cofoundressesthan when alone, and that within associations the queen losingmore weight is more likely to die. In this study, we testedwhether queens adjust weight loss to social environment andfighting ability and whether restraining weight loss directlyincreases survival prospects. Experimental manipulation of coloniesshowed that reduced investment by queens within associationsis primarily a response to the presence of a nest mate and notsimply a response to per-queen brood-care demands. Differencesin head width were associated with relative and combined weightloss of cofoundresses, as well as with queen survival. In contrast,the investment strategies of queens were not significantly influencedby their nest mates' initial weight. Similarly, manipulationof the queens' relative weight by feeding and exposure to contrastingsocial environment (queens kept alone or in groups) did notsignificantly affect survivaL These results indicate that headwidth differences or correlated phenotypic atthbutes of fightingability influenced both investment strategies and survival probabilityof queens. That queens with larger heads invested less energyinto brood rearing and were more likely to survive reveals moreselfish interactions among cofoundresses than has previouslybeen assumed and casts some doubts about the idea that groupselection must be invoked to account for the maintenance ofcooperation in foundress associations of ants.     

The impact of caging the queens during the flow season on some biological activities of honeybee colonies

This study was achieved in a private apiary located in a banana farm in Sa El Hagar, Basioun, Gharbia, Egypt from August 15, 2019 to May 25, 2020, including the banana (Musa sp., Musaceae) flow season (August and September) and extend to Egyptian clover (Trifolium alexandrinum L., Fabaceae) flow season (May). The study aimed to evaluate the effect of confining the queen during the banana flow season on the brood rearing, honey yield, and activation of worker's ovaries. Also, we determined the negative impact of caging the queen during the banana flow season on the activity of the colony in brood rearing, storing pollen, and honey yield after releasing the queen on 5 October, extending to the next flow season in May. The obtained results showed that the honeybee colonies with the caged queen produced significantly more honey yield and less brood production than the free queen ones during the banana flow season. Also, the caging of the queen did not affect the colony strength after releasing the queen despite the partial development of the ovaries of some workers, but they did not lay eggs. In addition, releasing the queens suppressed the ovaries of the laying workers. It can be concluded that caging the queen during the banana flow season helps the colonies to produce more honey yield without effect on the colony strength after releasing the queen despite the ovaries development of few workers without egg-laying.     

Dynamics of colony emigration in the ant Aphaenogaster senilis

In many social insect species, colonies frequently emigrate to a new nest. This requires the coordination of many individuals, and it puts the queen at risks of being lost or predated. We experimentally studied colony emigration in the ant Aphaenogaster senilis, who emigrates frequently and obligatorily reproduces by colony fission. As in other species, colony emigration was characterised by a synchronised relocation of workers. Foragers found the new nest site and triggered the relocation of the “inside” workers, which built up following a sigmoid curve. Unlike in Temnothorax, where workers are transported to the new nest, most individuals relocated by walking. The brood was transported around the middle of colony relocation, mostly by “inside” workers because they represent most of the workforce. The queen walked to the new nest at the middle of colony relocation, when the flow of ants to the new nest was maximal. Overall, this temporal dynamic of colony emigration is similar to that observed in other species. However, we argue that species-specific traits, such as whether workers are transported to the new nest or relocate by themselves, may affect parts of the process of colony emigration.     

The influence of social structure on brood survival and development in a socially polymorphic ant: insights from a cross‐fostering experiment

Animal societies vary in the number of breeders per group, which affects many socially and ecologically relevant traits. In several social insect species, including our study species Formica selysi, the presence of either one or multiple reproducing females per colony is generally associated with differences in a suite of traits such as the body size of individuals. However, the proximate mechanisms and ontogenetic processes generating such differences between social structures are poorly known. Here, we cross‐fostered eggs originating from single‐queen (= monogynous) or multiple‐queen (= polygynous) colonies into experimental groups of workers from each social structure to investigate whether differences in offspring survival, development time and body size are shaped by the genotype and/or prefoster maternal effects present in the eggs, or by the social origin of the rearing workers. Eggs produced by polygynous queens were more likely to survive to adulthood than eggs from monogynous queens, regardless of the social origin of the rearing workers. However, brood from monogynous queens grew faster than brood from polygynous queens. The social origin of the rearing workers influenced the probability of brood survival, with workers from monogynous colonies rearing more brood to adulthood than workers from polygynous colonies. The social origin of eggs or rearing workers had no significant effect on the head size of the resulting workers in our standardized laboratory conditions. Overall, the social backgrounds of the parents and of the rearing workers appear to shape distinct survival and developmental traits of ant brood.     

Cooperative nest‐defence behaviour and territory quality in a resident and socially monogamous passerine

Nest defence is a fundamental aspect of parental care in secondary cavity‐nesting birds, and predation or competition for nesting sites can involve different defensive behaviours. Because habitat quality determines breeding success, we were interested in whether breeding pairs of the Eurasian nuthatch, Sitta europaea, established in more favourable environment also manifest higher probability of cooperative behaviour during their nest‐site defence. To explore this relationship, we quantified behavioural displays of both parents and analysed activity budget ethogram data from simulated territorial intrusions performed in the chick‐feeding phase with one conspecific and two different heterospecific stimuli (dummies of nuthatch, starling and woodpecker). We found that paired individuals shared their roles during nest‐site defence to a considerable extent. Males had a significantly higher number of attacks on intruders than females, and females performed more threat displays and controls of the brood than males. Multinomial analysis of the cooperative behaviour suggested that pairs in a high‐quality territory had higher probability of reciprocal substitution of different roles towards a balance between attacks, threat displays and nest controls. Contrary to this, pairs in a low‐quality territory had less likely pairwise combinations of simultaneous behavioural states that are associated with effective nest‐site defence. The difference in response probability according to territory quality was, however, highly variable in view of the stimulus that was used in simulated territorial intrusion. Because individual roles and the complex behavioural repertoire of pairs altered in response to territory quality and potential nest‐site competitor or brood predator, our results suggest that the cooperative nest‐defence behaviour could be linked to the breeding success of this year‐round territorial species living in a heterogeneous forest habitat.